Issue 3/2024

AVIATION
SAFETY
LETTER
IN THIS ISSUE…

Ensuring Safe Winter Operations:

Best Practices for De/Anti-Icing in Aviation
In-flight Icing
Soar Spots: A Review of Glider Conflictions in Canada
Back Into the Circuit—Changes to the TC AIM
Psychological Safety in Aviation
TP 185E

Cover photo: iStock

 ASL 3/2024

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ISSN: 0709-8103
TP 185E

Table of Contents
Page

Ensuring Safe Winter Operations: Best Practices for De/Anti-icing in Aviation ................................ 3
Transport Canada’s Flight Crew Recency Requirements Self-paced Study Program ........................ 5
In-flight Icing ...................................................................................................................................... 6
Soar Spots: A Review of Glider Conflictions in Canada.................................................................... 11
Back into the Circuit—Changes to the TC AIM ................................................................................ 18
TSB Report A18P0031—Loss of control and collision with terrain ................................................. 22
Submission of Aviation Safety Letter (ASL) articles ......................................................................... 39
Civil Aviation Documents Issued Recently ....................................................................................... 40

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Ensuring Safe Winter Operations: Best Practices for

De/Anti-icing in Aviation
by Yvan Chabot, A/Chief, Commercial Flight Standards, Civil Aviation, Transport Canada

With winter on the horizon, the aviation community needs to remain alert to the risks of flying in snow
and icing conditions. Transport Canada (TC) is providing this information to renew everyone’s awareness
regarding aircraft operations in icing conditions.

The Impact of Ice and Snow on Aircraft and the Importance of De-icing and Anti-icing
Inspections
Research and past incidents
have shown that even a thin
layer of frost can disrupt
airflow over an aircraft’s lift
and control surfaces,
potentially leading to
increased drag, loss of lift
and impaired
maneuverability.
Additionally, ice can increase
the aircraft’s weight,
interfere with control surface
movement or hinder the
functionality of critical
sensors. Therefore, it is
crucial to ensure that all
critical surfaces of an aircraft
are free from contamination
before take-off.

This can be verified by the

pilot-in-command (PIC) or
by trained and qualified
personnel through a Credit: Shutterstock
pre-take-off contamination inspection. The PIC must ensure that aircraft critical surfaces are free of contamination
prior to take-off. If the inspection is delegated, an inspection report must be provided to the PIC, who must confirm
understanding. Detailed communication guidelines should be in the operator’s manual/ground icing program (GIP),
as applicable.

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Holdover Time Guidelines

The holdover times (HOT) for aircraft de/anti-icing fluids (ADF) are available in the Transport Canada HOT
Guidelines. The HOT Guidelines indicate how long ADFs remain effective against numerous icing conditions.
Since various factors may influence these times (e.g., precipitation intensity or temperature change, prevailing
winds) the PIC must be aware of these factors and adjust the applicable HOT accordingly. The operators’
manuals/GIP should outline these factors and procedures when using the HOT Guidelines.

Aircraft De/Anti-icing Fluid Considerations

Operators requiring a GIP must have a training component that ensures all personnel applying ADF be properly
trained (e.g., use consistent application techniques, inspection procedures).

Only ADFs stored, dispensed and applied according to manufacturers’ instructions should be used, as these have
been tested against industry standards. It is important to also ensure that ADFs are within specifications (e.g., lowest
on-wing viscosity [LOWV], highest on-wing viscosity [HOWV]) to ensure that holdover times can be safely
attained and that the ADF can be used down to its Lowest Operational Use Temperature (LOUT). Using fluids not
within their specifications could impact their expected performance and compromise take-off performance.

Recommended Actions for Safe Operations

Pilots, service providers and other personnel involved in de/anti-icing operations should familiarize themselves
with the applicable Canadian Aviation Regulations (CARs) and Standard 622 of the General Operating and Flight
Rules Standards (GOFRS)—Ground Icing Operations. They should also adhere to procedures recommended by the
aircraft manufacturer and comply with all company operations manual (COM) provisions.

Guidance Documents
• Transport Canada’s TP 14052—Guidelines for Aircraft Ground Icing Operations provides
detailed information on application methods, fluid types and more. It is a valuable
resource for ensuring safe operations in ground icing conditions.

• The holdover times for SAE-qualified de/anti-icing fluids are obtainable in the Transport
Canada HOT Guidelines.
By adhering to these best practices and guidelines, pilots, operators and service providers can ensure safe and
efficient operations during the winter season. Maintaining vigilance and proper procedures will help mitigate the
risks associated with flying in icy conditions, ensuring the safety of all involved. 

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Transport Canada’s Flight Crew Recency Requirements

Self-paced Study Program
The Flight Crew Recency Requirements Self-paced Study Program is no longer published in its entirety in the
Aviation Safety Letter (ASL). With the expansion of the exam and technological advances, it was determined to be
more convenient to complete the exam online. Each year, a reminder will be published in the ASL with a link to
the exam to remind readers that it is available online.

It is important to note that a printable version of the exam is still available online as a PDF.

If you have any questions or comments regarding the Flight Crew Recency Requirements Self-paced Study
Program, please send an e-mail to the flight crew licensing group at:
PilotLicensing-LicencesdePilote@tc.gc.ca.

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In-flight Icing
Information gathered from Skybrary

Definition

In-flight airframe icing occurs when supercooled water freezes on impact with any part of the external structure of
an aircraft during flight.

Description
Although the nominal freezing point of water is 0°C, water in the atmosphere does not always freeze at that
temperature and often exists as a "supercooled" liquid. If the surface temperature of an aircraft structure is below
zero, then moisture within the atmosphere may turn to ice as an immediate or secondary consequence of contact.

Considerable quantities of atmospheric water continue to exist in liquid form well below 0°C. The proportion of
such supercooled water decreases as the static air temperature drops to -40°C (except in cumulonimbus [Cb] clouds,
where supercooled large droplets [SLD] may exist at even lower temperatures); almost all of it is in solid form. The
size of supercooled water droplets and the nature of the airflow around the aircraft surface determine the extent to
which these droplets will strike the surface. The size of a droplet will also affect what happens after such impact;
for example, larger droplets will often be broken up into smaller ones. Finally, since the size of a water droplet is
broadly proportional to the mass of water it contains, and this mass determines the time required for the physical
change of state from liquid (water) to solid (ice) to occur, larger droplets which do not break up into smaller ones
will take longer to freeze because of the greater release of latent heat and may form a surface layer of liquid water
before this change of state occurs.

Airframe Icing Effects

Airframe icing can lead to reduced performance, loss of lift, altered controllability and, ultimately, stall and
subsequent loss of control of the aircraft. Hazards arising from the presence of ice on an airframe include:

Adverse aerodynamic effects

Ice accretion on critical parts of an airframe unprotected by a normally functioning anti-icing or de-icing system
can modify the airflow pattern around airfoil surfaces, such as wings and propeller blades, leading to loss of lift,
increased drag and a shift in the airfoil centre of pressure. The latter effect may alter longitudinal stability and pitch
trim requirements. Longitudinal stability may also be affected by a degradation of lift generated by the horizontal
stabilizer. The modified airflow pattern may significantly alter the pressure distribution around flight control
surfaces such as ailerons and elevators. If the control surface is unpowered, such changes in pressure distribution
can eventually lead to uncommanded control deflections, which the pilot may not be able to be overpower.

Blockage of pitot tubes and static vents

Partial or complete blockage of the air inlet to any part of a pitot static system can produce errors in the readings of
pressure instruments such as altimeters, airspeed indicators and vertical speed indicators. The most likely origin of
such occurrences to otherwise serviceable systems has been the non-activation of the built-in electrical heating
which these tubes and plates are provided with, although in some cases, the detail design of pitot heads has made
them relatively more vulnerable to ice accretion, even when functioning as certificated. It is now also recognized

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that the effects of high-level ice crystal icing can have what are usually transient effects on the effectiveness of
normally functioning pitot probe heating.

Radio communication problems

Historically, ice forming on some types of unheated aerials has been the cause of degraded performance of radios,
but this has not been encountered in the case of modern radio equipment and aerials.

Surface hazard from ice shedding

Ice shed during in-flight de-icing is not of a size
which could create a hazard should it survive in
frozen form until reaching the ground below.
However, there has been a long history of ice falls
from aircraft waste drain masts, a few of which
have caused minor property damage and
occasionally come close to hitting and injuring
people. The drain masts involved are those from
aircraft galleys or toilet compartments which are
normally heated to prevent ice formation, but, for
some reason, have not been operating as intended.
Ice from toilet waste masts is often referred to as
"blue ice." Most of these events have been
recorded where there is a high density of long-haul
commercial air traffic inbound to a large airport
which routinely overflies a densely populated
residential area as it descends below the freezing Rime ice
level in the vicinity of the airport. Credit: Bruce Sinclair

The Airframe Ice Accretion Process

Ice accretion on an aircraft structure can be
distinguished as rime icing, clear/glaze icing or a
blend of the two referred to as cloudy or mixed
icing:

Rime ice
Rime ice is formed when small, supercooled water
droplets freeze rapidly on contact with a sub-zero
surface. The rapidity of the transition to a frozen
state is because the droplets are small, and the
almost instant transition leads to the creation of a
mixture of tiny ice particles and trapped air. The
resultant ice deposit formed is rough and
crystalline and opaque, and because of its
crystalline structure, it is brittle. It appears white in
colour when viewed from a distance: for example,
Rime ice
from the flight deck when on a wing leading edge.
Credit: Bruce Sinclair

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Since rime ice forms on leading edges, it can affect the aerodynamic characteristics of both wings and horizontal
stabilizers, as well as restrict engine air inlets. Rime may begin to form as a rough coating of a leading edge, but if
accretion continues, irregular protrusions may develop forward into the airstream, although there are structural
limits to how much “horn” development can occur.

Clear ice
Clear or glaze ice is formed by larger supercooled water droplets, of which only a small portion freezes
immediately. This results in runback and progressive freezing of the remaining liquid, and since the resultant
frozen deposit contains relatively few air bubbles as a result, the accreted ice is transparent or translucent. If the
freezing process is sufficiently slow to allow the water to spread more evenly before freezing, the resultant
transparent sheet of ice may be difficult to detect. The larger the droplets and the slower the freezing process, the
more transparent the ice.

Occasionally, certain temperature and droplet size combinations can lead to the formation of a “double ram’s horn”
shape forward of the leading edge, with protrusions from both the upper and lower leading edge surfaces. These
horns have been observed to occur in a variety of forms in a wide range of locations along a leading edge and,
because clear ice has a more robust structure than rime ice, they can reach larger sizes.

Cloudy or mixed ice

This blend of the two accreted ice forms in the wide range of conditions between those which lead to mostly rime
or mostly clear/glaze ice and is the most commonly encountered. Its appearance will be determined by the extent
to which it has been formed from supercooled water droplets of various sizes.

Some other terms which may be encountered in connection with airframe ice accretion include:

Supercooled large droplets (SLD)

"Supercooled large droplets are defined as those with a diameter greater than 50 microns”—The World
Meteorological Organisation”

“Supercooled Large Droplet....[has] a diameter greater than 50 micrometers (0.05 mm). SLD conditions include
freezing drizzle drops and freezing raindrops.”2—FAA AC 91-74A, Pilot’s Guide to Flight in Icing Conditions

If a SLD is large enough, its mass will prevent the pressure wave travelling ahead of an airfoil from deflecting it.
When this occurs, the droplet will impinge further aft than a typical cloud-sized droplet, possibly beyond the
protected area and form clear ice.

Droplets of this size are typically found in areas of freezing rain and freezing drizzle. Weather radar is designed to
detect large droplets, since they are not only an indication of potential in-flight icing but also updrafts and wind
shear.

Runback ice
Runback ice forms when supercooled liquid water moves aft on the upper surface of the wing or tailplane beyond
the protected area and then freezes as clear ice. Forms of ice accretion which are likely to be hazardous to continued
safe flight can rapidly build up. Runback is usually attributable to the relatively large size of the SLD encountered
but may also occur when a thermal ice protection system has insufficient heat to evaporate the quantity of
supercooled water impinging on the surface.

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Intercycle ice
Intercycle ice is that which forms between cyclic activation of a mechanical or thermal de-icing system.
Accumulation of some ice when these systems are not 'on' is an essential part of their functional design. The time
interval between 'on' periods is usually selectable between at least two settings. Any ice remaining after a de-icing
system of this type has been selected off is sometimes referred to as residual ice.

The Adverse Aerodynamic Effects of Accreted Ice

The aerodynamic effects of accreted ice on the continued safe flight of an aircraft is a complex subject because of
the many forms such ice accretion can take. In certain circumstances, very little surface roughness is required to
generate significant aerodynamic effects and, as ice load accumulates, there is often no aerodynamic warning of a
departure from normal performance. Stall warning systems are designed to operate in relation to the angle of attack
on a clean aeroplane and cannot be relied upon to activate usefully in the case of an ice-loaded airframe.

Icing in Cloud and Precipitation

Any cloud containing liquid water can present a significant icing environment if the temperature is 0°C or less.
Generally, cumuliform cloud structures will contain relatively large droplets, which can lead to very rapid ice
build-up. Stratiform cloud structures usually contain much smaller droplets, although the horizontal extent of icing
conditions within a stratiform cloud may be such that the accumulation in even a relatively short period of level
flight can sometimes be considerable. The most significant ice accretion in any cloud can be expected to occur at
temperatures below but close to 0˚C. In a stratiform cloud in temperate latitudes, the maximum ice accretion is
often found near the top of the cloud, and it may be unwise for some turboprop aircraft to remain at such an altitude
for extended periods.

Any drizzle or rain which is encountered at temperatures of freezing or below is likely to generate significant ice
accretion in a very short period of time, even if reasonable forward visibility prevails, and such conditions should
be exited by any appropriate change of flight path.

Snow, in itself, does not present an icing threat, since the water is already frozen. However, snow can be mixed
with liquid water, particularly cloud droplets, and, in some circumstances, can contribute to the accumulation of
hazardous frozen deposits. This phenomenon may also occur in cumulonimbus anvil clouds, where the ice crystals
may be mixed with SLD to incur significant icing.

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Types of In-flight Airframe Icing Accidents

There are two main origins of accidents and serious incidents involving airframe icing:

1. General aviation aircraft that are not equipped with ice protection systems but are flown
in icing conditions may encounter enough icing at cruise altitudes to overwhelm the
aircraft power reserve, leading to an inability to maintain altitude and/or airspeed. In
mountainous terrain, this very often leads to a stall followed by a loss of control when the
pilot attempts to maintain altitude over the high terrain. Alternatively, a collision with
terrain may result when altitude cannot be maintained. Regardless of the type of terrain,
any aircraft without airframe ice protection systems which is flown in icing conditions
can quickly encounter a stall and loss of control due to the excessive drag and loss of lift
which ice accretion can bring.
2. Aircraft, predominantly propeller-driven, which rely on wing and tail ice protection by
de-icing, principally by pneumatic deicing boots and are operated in icing conditions
which exceed the capability of the protection. In these cases, if the angle of attack
increases in the presence of an abnormal ice loading either as a result of attempting to
maintain a climb with limited power and a relatively high load or, more suddenly, when
configuration is changed during the approach to land, a stall and loss of control can result
from which recovery may not be possible at low level.

Solutions
• flight planning. For aircraft without airframe ice protection systems, operation in icing
conditions should be avoided. This can only be assured if operating in visual
meteorological conditions (VMC) and flight in freezing precipitation will not occur, or in
instrument meteorological conditions (IMC), when temperatures will be above freezing
and flight in freezing precipitation will not occur. It is particularly important that the
cruise portion be planned so as to avoid icing at high altitudes above mountainous terrain.
• operation of ice protection systems. Care should be taken to operate the wing and
tailplane ice protection systems in accordance with the manufacturer's specification. In
recent years, there have been significant changes in procedures for effective operation of
pneumatic ice protection systems, and these instructions should not be ignored in favour
of popular notions such as ice bridging.
• approach and landing. Pilots operating ice-protected aircraft should consider the effects
of any residual ice which may be present during approach and landing, since it may
degrade performance substantially and lead to abnormal responses to configuration
changes.

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Soar Spots: A Review of Glider Conflictions in Canada

by Nicholas van Aalst, Safety & Quality, NAV CANADA

Nicholas (Nick) van Aalst is an air traffic controller assigned to Safety & Quality at NAV CANADA and a graduate
student from Embry-Riddle Aeronautical University, previously having served as faculty at Mount Royal University
and holding a commercial pilot’s license, group 1 instrument rating, as well as a glider pilot’s license.

The author thanks the tremendous contributions of Dr. Jonathan Histon, Manager, Human Performance and the
wider Safety & Quality Department at NAV CANADA for article development and subject matter expertise.
Additional acknowledgement goes to Captain Ashley Gaudet of 2 Canadian Air Division, as well as Mr. David
Donaldson of the Soaring Association of Canada.

Correspondence regarding this article can be addressed to NAV CANADA and Safety & Quality via
Nicholas.vanaalst@navcanada.ca.

Soar Spots
During the late morning of August 12, 2022, a Boeing 767-375ER was conducting an instrument landing system
approach to Hamilton, Ontario’s Runway 12 when a glider rapidly filled the crew’s windscreen, forcing the crew
of the 767 to take evasive action, passing close enough to clearly observe the glider pilot. Fortunately, both aircraft
were able to continue and make normal landings without further incident (Aviation Safety Network, 2022). This
event illustrates the challenges and importance of airspace deconfliction and interactions between glider operations
and other airspace users.

The Safety & Quality (S&Q) team at NAV CANADA has identified glider operations as a driver for conflicts with
a heightened risk of collision within controlled airspace. Several features of glider operations contribute to this risk
driver, including constraints on human performance, air traffic control operational limitations including airspace
requirements, as well as the limitations on aircrew and their operational requirements. In varied and dynamic
combinations of these factors, the result may render a degraded state of situational awareness and collective mental
modelling leading to a mishap. Via awareness for this type of confliction, this article will provide insights into some
of the pre-conditions for events, such as occurred in Hamilton, and provide readers with interest-based best practices
for prevention.

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Background
On August 28, 2006, a Hawker 800XP on descent near Reno, Nevada—collided with a Schleicher ASW 27 glider,
as seen in Figure 1, at approximately 16 000 ft above sea level. According to the National Transportation Safety
Board (NTSB) report (Charnon, 2008), “…damage sustained by the Hawker disabled one engine and other systems;
however, the flight crew was able to land the airplane. The damaged glider was uncontrollable, and the glider pilot
bailed out and parachuted to the ground” (p. 1). The NTSB’s findings indicated that the closure rate between the
aircraft rendered collision avoidance was improbable, if not impossible once the conflict became apparent.
Moreover, the lack of a transponder signal from the glider led to a degraded state of air traffic control (ATC) and
aircrew situational awareness, which contributed to the mishap.

Method

The S&Q department has conducted a review of probable glider confliction areas in Canada, including transponder
and ATC service provision requirements. This analysis further examined operating locations, including adjacent
airspace and stakeholder interactions. Moreover, the review explored limitations of “see and be seen” and “see and
avoid” principles associated with visual meteorological conditions (VMC) for both visual flight rules (VFR) and
instrument flight rules (IFR) aircraft.

Figure 1: Schleicher ASW 27 glider, (Münch, n.d.)

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Figure 2: Hawker 800XP following a mid-air collision with glider

(National Transportation Safety Board, 2006)
From this review, three key elements of conflicts, including their relationships, were identified as
summarized below, as well as in Figure 3.

1. human performance limitations

2. ATC operational limitations
3. aircrew operational limitations

Where limitations in Figure 3 overlap and interact, conflicts are more likely to occur. The following sections
describe these interactions in greater detail.

Human Performance Limitations

The subject of human performance is a cross-discipline conversation requiring an understanding of situational
awareness and perceptual blindness affecting mental modelling.

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Conflictions
Human
Performance
Limitations

ATC Aircrew
Operational Operational
Limitations Limitations

Figure 3: Risk driver relationships and interactions

Situational Awareness
Situational awareness (SA) is generally comprised of three levels: detection, understanding and prediction.
First and foremost, detection requires aircrew and ATC to sense information regarding the environment.
Second, aircrew and ATC must understand the meaning of the information, ultimately leading to the third
level of situational awareness: the predicting of future needs.

Reflecting on the events of Reno, Nevada, and Hamilton, Ontario, what is apparent is that SA was not complete
prior to the gliders being spotted. However, SA was rapidly restored, although with varied outcomes, with time
being the critical factor in conflict resolution.

Perceptual Blindness
While levels of SA are built on our ability to sense the world around us, phenomenon such as perceptual
blindness, also referred to as inattention blindness, involve failing to observe what may be considered obvious.
Similarly, it is plausible that cognitive capture can promote a fixation upon a task, an object or even a thought, at
the expense of SA.

What is apparent from stakeholders is that gliders are rarely forming a component of SA, largely due to low priming
on the threat associated with gliders and a bias towards power-driven aircraft during traffic lookouts. Additionally,
research indicates that inconspicuous coloration of objects may play a role in perceptual blindness. When applied
to low-profile design gliders—predominantly white in colouration—the ability to visually identify gliders is
reduced.

ATC Operational Limitations

ATC is often relied upon for traffic information to augment aircrew SA. Simultaneously, control instructions and
clearances are provided based on known traffic with transponder-derived secondary surveillance radar and space-
based surveillance data. However, under Canadian Aviation Regulation 605.35, gliders are permitted to operate

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within significant segments of Canadian domestic airspace without a transponder and altitude encoding equipment.
This renders gliders as effectively invisible across vast areas of airspace, with only occasional primary radar returns
being possible, which may represent any number of objects, including but not limited to birds.

Moreover, with primary radar returns not rendering altitude information and with primary radar returns being quite
frequent, it may be challenging for ATC to provide relevant traffic information, particularly due to workload. To
better manage workload, ATC may heavily rely upon altitudes for traffic separation, such as when aircrew adhere
to standard altitudes based on flight rules and direction of flight. However, the nuance and inability of gliders to
maintain constant altitudes means gliders pass through altitudes of IFR and VFR aircraft, suggesting a wide rang
of altitudes where conflictions may occur.

Aircrew Operational Limitations

Having explored the concepts of human performance and limitations for ATC, operating limitations for aircrew
in VMC, as well as available publications, deserves some consideration.

VMC Visual Separation

Whether operating as VFR or IFR, aircrews in VMC rely on mantras of “see and be seen,” as well as “see
and avoid” for deconfliction. Of these, three elements appear:
1. a traffic lookout
2. being visible
3. resolving conflicts

Glider visibility. From the vantage point of a glider pilot, traffic lookout is counter-intuitively limited, even with
the visibility afforded by canopy designs. Restrictions of visibility include the wingspan and wing position, as
well as the positioning of the pilot’s seat. As gliders may operate for extended periods at high bank angles and
high rates of turn, glider pilots are challenged to maintain effective lookouts in rapidly changing environments. In
turn, from a third-party perspective, the ability to observe a tightly orbiting glider can be difficult, particularly
with low-profile designs and the absence of anti-collision lighting.

Power-driven aircraft. When discussed from the perspective of power-driven aircraft, physical obstructions limit
visibility. However, a deeper challenge presents a conflict between the “heads up” monitoring of displays and
effective traffic lookouts, with cockpit workload becoming increasingly predominant in modern general aviation
aircraft.

Right-of-way-based deconfliction. CAR 602.19–Right of Way contains significant information regarding

deconfliction. Most notable in the hierarchy is the priority of gliders, potentially rendering some measure of
complacency for glider pilots, although VMC presents with shared responsibility for traffic detection and
deconfliction.

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Publications
A review of aeronautical publications, including applicable NOTAMs, has revealed that gliding operations are not
clearly defined, nor are glider pilots required to remain confined to Class F airspace or as depicted on VFR
navigation charts. This finding is not limited to VFR publications, as there is less clarity on IFR publications,
including STARs and approach plates, suggesting that IFR traffic may have a degraded level of SA.

Addressing NOTAMs specifically, a published glider operations NOTAM may serve to reinforce glider pilot
complacency under the assumption that NOTAMs are widely and thoroughly reviewed and understood.

A Probable Confliction Scenario

Based on the drivers in Figure 3, identifying probable confliction locations within Canada required S&Q to explore
areas with a mixed requirement for ATC clearances, communication, navigation and surveillance, coupled with
significant mixed flight rules and performance elements. Further review suggests that this complexity occurs more
frequently within Class E airspace, where VFR aircraft operate without the element of a control service and where
transponder requirements vary in accordance with the Designated Airspace Handbook. Consequently, Class E
airspace is a probable driver for conflictions within controlled airspace.

As such, consider the scenario of an IFR aircrew during arrival and approach phases of flight, descending through
a small area of Class E airspace on an ATC clearance, prior to transitioning into a terminal control area or control
zone. During this time, this crew may face heightened cognitive workloads and competing priorities—covering
distances upwards of four nautical miles per minute—transitioning between VMC and IMC through scattered or
broken cumulus clouds, as depicted in Figure 4. In a multi-crew environment, workload factors for the pilot
monitoring include direct controller–pilot communications and other “heads down” duties, requiring significant
crew resource management skills.

Consider now the perspective of the VFR glider pilot, operating within the same segment of Class E airspace,
relying upon rising air beneath a cumulus cloud through which the previously mentioned IFR aircraft, is about to
pass. In this scenario, absent a requirement for communication and surveillance-related equipment, gliders are
unable to contribute to the shared mental modelling of the IFR aircrew and ATC, nor are gliders fully aware of the
related traffic picture. It is here that the pre-conditions for a confliction are present, and it is here that conflicts, such
as previously depicted in Hamilton and Reno, potentially develop.

How You Can Stay Classy in Class E

As the prevalence of threat has presented predominantly within Class E airspace, including across airways where
aircrew and ATC may not be aware of glider operations, specific locations for conflictions are vast and challenging
to predict. However, during stakeholder engagement with S&Q, perhaps the most impactful moment came in the
form of a philosophical quote: “…talk to the people who can kill you!”, crystalizing the core concept that awareness
and collaboration drive effective flight safety initiatives.

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Figure 4: Glider pilot perspective under cumulus cloud (Sosinski, 2024)

Recommended Best Practices

Recalling Figure 3, prominent best practices surfaced towards the development, maintaining and recovering of
situational awareness and may largely be divided by perspective.

Glider Pilots

1. Study airspace prior to flight operations and be aware of IFR and VFR traffic flows,
including STARs and instrument approaches.
2. Provide frequent and accurate position reporting on enroute frequencies.
3. Develop rapports with adjacent operators and ATC units while adhering to localized
agreements and best practices.

Power-driven Aircraft Pilots

1. Study publications prior to flight operations and be familiar with adjacent aerodromes
and airspace that support glider operations.
2. Where practicable, monitor for traffic on the enroute frequency, and provide position
reports.
3. Be deliberate and critical when conducting traffic lookouts in VMC.

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Air Traffic Controllers

1. Where practicable, provide information on known and unverified traffic, including

primary targets that are persistent or steady state, in areas where gliders may be present.
2. Develop a rapport with glider operators to engage and inform on operational impacts.
3. Where required, develop, verify and validate localized procedures for glider operations.

Conclusion
What S&Q’s review has shown is that glider conflictions are driven by three key enablers: human, ATC, and aircrew
operational limitations and requirements. Further degrading situational awareness are aircraft operating without a
transponder, such as the case with many gliders in Canada. As a result, best practices towards deconfliction in
advance of operations, as well as during operations, including frequent and effective communications and
stakeholder engagement. These practices are crucial in preventing airborne conflictions such as those having
occurred in Hamilton, and mishaps such as Reno, and may serve wider benefits to the aviation ecosystem
in Canada. 

References

• Aeronautics Act. Canadian Aviation Regulations, 602.19 (2021)

• Aeronautics Act. Canadian Aviation Regulations, 605.35 (2022)
• Aviation Safety Network. (2022). CargoJet Airways Boeing 767-375ER C-FCAE. Flight Safety Foundation
• Charnon, N. (2008). Aviation Investigation Final Report LAX06FA277. National Transportation Safety Board
• Münch, M. (n.d.). Schleicher ASW 27 glider [image]
• National Transportation Safety Board. (2006). Hawker following mid-air collision with glider [image]
• Perera, A. (2023, September 7). Inattentional blindness in psychology. Simply Psychology
• Sosinski. (2024). Glider pilot perspective under cumulus cloud [image].
• Transport Canada. (2024). Aeronautical Information Manual. Minister of Transport. Ottawa, Ontario

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Back into the Circuit–Changes to the TC AIM

by Uwe Goehl, Civil Aviation Safety Inspector, Transport Canada, General Flight Standards

Unless you are a balloon pilot, you have probably spent a fair amount of time flying in an aerodrome traffic circuit.

Student pilots pursuing an Ultralight Aeroplane Permit, Recreational Pilot Permit or Private Pilot Licence spend a
considerable part of their training in the circuit, logging and perfecting take-offs, approaches and landings. Not only
are traffic circuits flown by aircraft operating under visual flight rules (VFR), but a traffic circuit may be part of a
visual approach, a contact approach or a circling approach flown by an aircraft operating under instrument flight
rules (IFR). It may even be the quick, safe method used by an aircraft to return to the aerodrome following a situation
during or right after take-off, such as an engine failure on a multi-engine jet in visual meteorological
conditions (VMC).

Aside from balloons, all sorts of aircraft of different configurations and with different performance capabilities
may fly a traffic circuit, from slow ultralight aeroplanes to much faster transport category jets. This can create
challenges when these aircraft with very different performance capabilities are operating at an aerodrome at the
same time. Because of this, Transport Canada’s Aeronautical Information Manual (TC AIM) had a significant
update to the guidance on flying visual circuits at controlled and uncontrolled aerodromes in edition 2024-2,
published on October 3, 2024.

The way pilots must operate their aircraft when flying near an aerodrome can be found in the Canadian Aviation
Regulations (CARs) Subpart 602, Division V. CAR section 602.96 closely mirrors the International Civil Aviation
Organization (ICAO) Standards and Recommended Practices (SARPs) published in ICAO Annex 2–Rules of the
Air, section 3.2.5. In a nutshell, both the CARs and the ICAO SARPs say that the pilot-in-command must:

• observe aerodrome traffic to avoid a collision;

• conform to or avoid the flow of traffic already established by other aircraft;
• make all turns to the left, unless otherwise instructed. In Canada, that instruction may be
given by ATC or published in the Canada Flight Supplement; and
• when practical, land into the wind.
This helps explain why traffic circuit procedures are the same in other countries (i.e., observe other traffic to avoid
a collision, conform to and avoid the pattern of traffic formed by other aircraft operating at the aerodrome and make
all turns to the left in a circuit, unless otherwise specified), while some procedures, such as recommended traffic
circuit entries, are different.

For example, in Canada, the preferred entry at an uncontrolled aerodrome is crossing the aerodrome mid-field. In
the United States, the preferred entry at a non-towered airport is at a 45-degree angle to the downwind leg.

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 ASL 3/2024

Diagram 1: Recommended standard left-hand traffic pattern at U.S.

non-towered airports with entry on a 45o angle to the downwind leg
Some countries chart the specific lateral track and altitude to be followed, depending on aircraft performance, for
each aerodrome.

While some elements of the traffic circuit are identical, these examples also underscore why it is important for a
pilot to thoroughly familiarize themselves with differences before flying in another country.

What’s changed and what hasn’t?

Here is the good news. It is very likely, whether you are an aeroplane, glider, rotorcraft or balloon pilot, that you
are already flying a traffic circuit as described in the updated edition of the TC AIM. We haven’t changed the
recommended traffic circuit entry procedures. We expect pilots to comply with the regulations, and we encourage
pilots to operate in accordance with published guidance information. In this case, though, the recommendations in
the TC AIM were lagging with respect to industry-accepted procedures and airline standard operating
procedures (SOPs), so the objective was to bring the TC AIM into alignment with the way many aircraft already,
and legally, fly traffic circuits. The new guidance is better harmonized with recommended aerodrome circuit

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procedures in other countries, such

as Australia and the United States.
However, if you are a light general
aviation aeroplane pilot, you may
not have been aware that jets and
turboprops typically conduct wider
circuits at 1 500 ft above ground
level (AGL). This makes sense
because they operate at higher
speeds and have greater turning
radii, so they cannot conform to the
flow of traffic formed by slower
single- and multi-engine aeroplanes.

If you are a jet pilot, you may be

unfamiliar with the modified circuits
flown by glider pilots. Most pilots
know that gliders have the right of
way over powered aircraft (they
cannot maintain altitude, and a
successful go-around is very
improbable). But did you know that Diagram 2: Charted lateral and vertical traffic circuit paths for helicopters,
aircraft towing gliders may follow light aircraft and high-performance aircraft at Flanders Airport, Belgium
what looks like an erratic departure
track to keep their glider within gliding distance of a safe landing spot, and that this is legal?

If you are a glider pilot, do you know what to expect from slow, low performing ultralight aeroplanes operating in
the circuit?

If you are a powered paraglider pilot flying a low, tight-traffic circuit at 20 mph, are you aware that you may be
sharing the circuit with gyroplanes and helicopters?

Rotorcraft pilots: there are several recommendations for you to fly the circuit depending on your performance
capabilities. Of course, helicopter pilots may choose to avoid the flow of traffic in the circuit(s), opting to arrive or
depart directly from the helipad at the aerodrome. But do you know what to expect from a balloon operating at an
aerodrome? Also, for helicopter pilots: the TC AIM has an update on helicopter operations at aerodromes in RAC
4.5.3.

Finally, for balloon pilots: do you know where and how other aircraft in the airspace around you manoeuvre near
an aerodrome?

It is important for pilots to have good situational awareness and to know what to expect from each other. The
objective is to ensure safety for everyone while providing fair aerodrome access to all legitimate airspace users,
regardless of the size or performance capabilities of their aircraft.

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 ASL 3/2024

Traffic circuits can get busy and increase pilot workload, especially at uncontrolled aerodromes. A few other
suggestions in the TC AIM can help minimize surprises and keep everyone safe:

• Keep a good look-out.

• Make yourself visible. Turn on your anti-collision (beacon/strobe) lights and landing
lights. It will make it easier for other pilots to see you.
• If you have a transponder, always use it, including the altitude encoding function. Even if
you are not in transponder airspace, you will be visible to aircraft using Aircraft Collision
Avoidance Systems (ACAS).
• Communicate, communicate, communicate! Speak clearly and concisely using the
recommended terminology. See NAV CANADA’s Phraseology Guides.
Note: Read more about United States non-towered airport flight operations. 

Note: Uwe is a qualified aeroplane, balloon, glider, gyroplane, RPAS and ultralight aeroplane pilot. Prior to
joining Transport Canada, if he wasn’t doing a visual circuit in an Airbus A320 or a gyroplane, he would do be
doing them in a sailplane, weight shift control aircraft, or in his powered paraglider.

TSB Report A18P0031—Loss of control and collision with

terrain
History of the flight
On February 23, 2018, the pilot planned to take nine passengers on a charter under instrument flight rules (IFR)
flight from Abbotsford Airport, BC (CYXX) to Long Beach/Daugherty Field/Airport, California, United States
(KLGB) using a company Beechcraft King Air B100 (King Air).

On the day of the occurrence, the pilot arrived at the hangar at approximately 0800. In the hours leading to the
departure, the pilot was involved in several different operational and business-related activities.

The pilot delegated most of the flight planning and pre-flight duties for the occurrence flight to the company staff
members. Due to concerns about the deteriorating weather at the airport where the flight was going to clear customs,
staff members were instructed to amend the operational flight plan, and arrangements were made to clear customs
at a different airport.

At approximately 1030, the passengers arrived and loaded and secured their own baggage in the rear baggage
compartment of the aircraft, using the supplied cargo net. The aircraft was in the hangar with the door closed to
protect it from contamination due to snowfall and to make it easier for passengers to board.

At 1121, the pilot called the Abbotsford air traffic control (ATC) tower to ask whether he could receive an early
clearance while the aircraft was still in the hangar. The pilot was concerned that, with the heavy snowfall, the
aircraft would be covered in snow if the flight experienced any delay in receiving the IFR clearance. Because the

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pilot's flight plan was not yet in the system, the pilot told the controller he would call back in 10 to 15 minutes for
his clearance.

At 1140, the pilot called ATC back and requested clearance over the phone; however, the controller was unsure if
that was allowed. The pilot then told the controller that he would have the aircraft towed out and would call on the
radio for the clearance. The pilot also mentioned the snow accumulation and his concern about the possibility of
having to wait for a clearance in the falling snow. The controller informed the pilot that there was one aircraft
inbound for landing, but that it should not significantly delay his departure.

The pilot and passengers boarded the aircraft and, at 1150, the hangar door was opened, and the aircraft was towed
outside. At this time, it was snowing.

At 1154, both engines were running. No de-icing or anti-icing fluid was applied to the aircraft. The pilot requested
and read back the clearance, and at 1155, he began taxiing to Runway 07.

Shortly after this time, the flight crew of the aircraft that had just landed on Runway 07 reported that they had had
the airport in sight when they were approximately 400 ft above ground level and that the braking action on landing
was moderate to poor.

At 1159, the pilot informed the controller that the aircraft was holding short for Runway 07. While the aircraft was
waiting for take-off clearance, no contamination was observed adhering to the wings. Two minutes later, the aircraft
that had just landed exited Runway 07, and the occurrence aircraft was cleared for take-off. At 1203, the aircraft
taxied onto the snow-covered Runway 07 and continued with an immediate take-off.

Approximately four to five seconds after take-off, the pilot selected the landing gear control to the up position. As
the gear retracted, the aircraft rolled approximately 30° to the left. To correct the uncommanded left bank, the pilot
applied right aileron, and the aircraft returned to a near wings-level attitude. In order to make an immediate
off-field emergency landing, the pilot retarded the power levers and then applied forward pressure on the control
column to land the aircraft. The aircraft struck terrain between Runway 07 and Taxiway C. The aircraft slid across
the snow-covered ground for approximately 760 ft before coming to rest in a raspberry patch located on the airport
property.

Personnel information

Pilot-in-command
The pilot held a Canadian airline transport pilot licence—aeroplane, with a type rating on the Beechcraft King
Air B100. His licence was endorsed with a Group 1 instrument rating and was valid until September 1, 2018.

Pilot's pre-flight planning

In the company, the pilot-in-command of a flight normally completed flight planning duties, including completing
the operational flight plan (OFP). However, it was the occurrence pilot's practice to delegate pre-flight planning
duties to other staff members.

In the hours leading up to the occurrence, the OFP was changed several times.

As a result, the OFP did not reflect the intended routing or fuel requirements.

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Aircraft information

General
The occurrence aircraft was imported from the United States in March 2017, and the Beechcraft Inspection Program
(Complete) was carried out at that time. The aircraft had accumulated 10 580.4 total time airframe hours.

There was no indication of a pre-existing system malfunction that may have played a role in the occurrence.

Stall warning system

The occurrence aircraft was equipped with a stall warning system, consisting of an indicator mounted on the left
side of the glareshield, a circuit breaker, a warning horn, and a heated lift transducer vane and face plate on the
leading edge of the left wing.

The investigation found no indication that the stall warning system activated during the occurrence flight.

Weight and balance

The investigation identified a number of errors on the OFP relating to weight and balance. Most notably, although
the aircraft had 549 lbs of fuel in the auxiliary tanks, 0 was entered on the OFP. There were no scales in the company
hangar, and several of the occupant weights, including those of the pilot and the passenger in the right-hand crew
seat, were incorrect. In addition, the distribution of these passenger weights on the OFP did not reflect the actual
seats occupied during the occurrence flight.

The OFP indicated that the aircraft was more than 600 lbs under the maximum allowable gross take-off weight of
11 800 lbs, and that the C of G was within the approved flight envelope. However, based on the actual occupant
and baggage weights and fuel loading, the investigation determined that the aircraft weighed approximately
12 000 lbs. The aircraft's C of G was near the aft limit of the approved envelope.

The pre-flight inspection did not ensure that the baggage was loaded properly.

Rear baggage compartment

The maximum allowable weight in the rear baggage compartment is 410 lbs. In addition, “all cargo shall be properly
secured by a Federal Aviation Administration–approved cargo restraint system.” In this occurrence, the passengers
loaded approximately 480 lbs of baggage in the rear baggage compartment, and the cargo stored in the rear baggage
compartment was secured using a cargo net. The investigation could not identify this net as an approved cargo
restraint system.

During the impact sequence, the cargo net failed to restrain the baggage stored in the rear baggage compartment.
One of the cargo net attachment points on the floor of the aircraft was pulled out, and the cargo net did not remain
connected to the other attachment points. Some of the baggage was projected forward into the cabin and struck
passengers seated at the rear of the cabin.

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 ASL 3/2024

Meteorological information

General
In the hours leading up to the accident, the Abbotsford area was under a low pressure system that brought snow and
reduced visibility with it and temperatures of approximately -2°C. At the time of the occurrence, moderate mixed
icing in cloud was forecast between 3 000 ft and 14 000 ft above sea level.

Aviation routine weather reports

The information in Table 1 was extracted from the aviation routine weather reports (METARs) at CYXX in the
hours prior to, and shortly after, the occurrence.

Time Wind Visibility (sm) Snow intensity Ceiling (ft) Temperature Dew point

1100 Calm ½ moderate 1 000 overcast -2oC -3oC

1127 080oT at 3 kt ⅝ moderate 700 overcast -2oC -3oC

1200* Variable at 2 kt ⅜ moderate 600 broken -2oC -3oC

1212 Calm ⅜ moderate 600 broken -2oC -3oC

1247 190oT at 8 kt ½ moderate 600 broken -2oC -3oC

1300 200oT at 5 kt ¾ light 800 broken -1oC -3oC

Table 1: METARs information for CYXX on the day of the occurrence (Source: NAV CANADA)
* The 1200 METAR information was the most current weather at the time of the occurrence.
The investigation was able to determine, using snowfall rate information from Abbotsford Airport, that the snowfall
rate had increased to approximately 2 cm per hour during the half hour before the occurrence. At this rate, the
amount of snow estimated to have fallen on the aircraft from the time it exited the hangar until it entered the runway
was about 4 to 5 mm.

The weather information for the area indicated that there may have been a layer of moist air near 0°C above the
surface level. This could have caused wet snow to form, with partially melted flakes and a higher water content
than would be expected for dry snow at the -2°C surface conditions.

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Snowfall intensity rating

For the purposes of METARs or Special Meteorological Reports (SPECI) and automated terminal information
service (ATIS) broadcasts, visibility is used to estimate snowfall intensity according to the following guidelines:

• Light: if visibility is ⅝ mi. or more

• Moderate: if alone1 and visibility is reduced to ½ or ⅜ mi.
• Heavy: if alone1 and visibility is reduced to ¼, ⅛ or 0 mi.
Note (1): “Alone” means no other precipitation and/or obstruction to vision is present.1

For de-icing and anti-icing purposes, snowfall intensity is an important consideration in determining holdover
time.2 Instead of relying solely on visibility as an indicator of snowfall intensity, industry and regulators have
established a snowfall intensity chart that takes lighting, temperature range and visibility into account (Table 2).

Lighting Temperature Range Visibility in Snow in Statute Miles (Metres)

o o
C F Heavy Moderate Light Very Light

Darkness -1 and above 30 and above ≤1 >1 to 2½ >2½ to 4 >4

(≤1600) (>1600 to 4000) (>4000 to 6400) (>6400)

Below -1 Below 30 ≤¾ >¾ to 1½ >1½ to 3 >3

(≤1200) (>1200 to 2400) (>2400 to 4800) (>4800)

Daylight -1 and above 30 and above ≤½ >½ to 1½ >1½ to 3 >3

(≤800) (>800 to 2400) (>2400 to 4800) (>4800)

Below -1 Below 30 ≤⅜ >⅜ to ⅞ >⅞ to 2 >2

(≤600) (>600 to 1400) (>1400 to 3200) (>3200)

Table 2. Snowfall intensities as a function of prevailing visibility

1
Environment and Climate Change Canada, MANOBS Manual of Surface Weather Observation Standards, Eighth
Edition (February 2019), section 6.6.2.5.3: Intensity by visibility, p. 6-35.

2
Holdover time “is the estimated time that an application of de-icing/anti-icing fluid is effective in preventing frost,
ice or snow from adhering to treated surfaces. Holdover time is calculated as beginning at the start of the final
application of de-icing/anti-icing fluid and as expiring when the fluid is no longer effective.” (Source: Transport
Canada, SOR/96-433, Canadian Aviation Regulations, Standard 622.11: Ground Icing Operations, section 2.0,
Definitions.)

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 ASL 3/2024

Based on the CYXX weather information (daylight, -2°C and ⅜ sm), the conditions at the time of the occurrence
fall into the heavy snowfall category. According to Transport Canada (TC) de-icing and anti-icing fluid guidelines,
no holdover guidelines exist for heavy snowfall, regardless of the type of de-icing or anti-icing fluid used, at any
temperature. In other words, in heavy snowfall, de-icing and anti-icing fluid is not considered an effective way of
combatting the risk of contamination during ground operations. International holdover guidelines put heavy snow
in the same category as ice pellets, moderate and heavy freezing rain, and small hail and hail.

Aerodrome information
The elevation of CYXX is 194 ft above sea level. CYXX has two runways. Runway 07/25 is asphalt/concrete and
measures 9 597 ft long and 200 ft wide, and Runway 01/19 is asphalt and measures 5 328 ft long and 200 ft wide.

To the north of Runway 07 is a parallel taxiway, Taxiway C. North of Taxiway C is a raspberry patch that is located
on the airport grounds.

At 1127, the ATIS reported the runway surface condition for Runway 07 as 80% trace dry snow and 20% bare and
damp. The runway surface condition information in the 1127 ATIS originated from a SNOWTAM/NOTAMJ
observation at 1048. The runway surface condition information had not been updated to reflect the increase in
snowfall between the 1048 SNOWTAM/NOTAMJ observation and the time of the occurrence. However, just
before the occurrence, ground operators reported that the Canadian runway friction index (CRFI) was 0.18, that
conditions were changing rapidly as the snowfall intensified, and that they were preparing to sweep the runway as
the occurrence aircraft departed. A CRFI reading of 0.18 represents the lowest value TC publishes for landing
distance corrections on contaminated runways.

Wreckage and impact information

Wreckage examination
The impact point was between Runway 07 and Taxiway C. The terrain at the initial point of collision was flat and
not frozen at the time of the occurrence; however, it was covered by approximately 3 cm of snow. After the initial
collision with terrain, the aircraft skidded about 760 ft across the ground and Taxiway C before it came to rest in a
raspberry patch about 800 ft left of the runway centreline and about 7 500 ft from the runway threshold (Figure 1).
The left wing broke off, just outboard of the left engine nacelle during the impact sequence.

Examination of the initial point of collision on the terrain showed three distinguishable ground scars (Figure 2).
The two long ground scars consistent with impact by the bottoms of the engine nacelles were on each side of a
ground scar, consistent with impact by the bottom of the fuselage. The maximum depth of this ground scar was
estimated to be greater than 1 inch (2.5 cm). Crushing to the bottom of the fuselage and both engine nacelles, as
well as the absence of signs of interaction between the right wingtip and the ground, indicated the aircraft had been
nearly level in pitch and roll when it collided with the terrain.

Performance calculations carried out at the TSB Engineering Laboratory determined that the vertical descent
velocity of the aircraft at the time of the crash (at the beginning of the impact) was estimated to be at least 20 fps.

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 ASL 3/2024

Figure 1: Occurrence aircraft where it came to rest (Source: Transport Canada)

Figure 2: The aircraft's initial point of collision with terrain and the direction of travel
(photograph taken February 27, 2018) (Source: TSB)

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 ASL 3/2024

During the wreckage examination, the propellers were removed and examined by the TSB with the assistance of
the propeller manufacturer's representative. No pre-existing condition that would have interfered with the normal
operation was identified in either propeller.

Both engines were removed and shipped to Honeywell Aerospace in Phoenix, Arizona for a teardown and
examination with a TSB investigator in attendance. The engine teardown and examination determined that the
damage to both engines was indicative of engine rotation and operation at the time of impact with the ground.
Functional testing of the engine control system, propeller governors and fuel controls identified no anomalies that
would have interfered with normal operation of the engines.

Due to impact damage, it was not possible to determine the integrity of the stall warning system with certainty.

Tests and research

Performance analysis
The investigation analyzed information from NAV CANADA secondary surveillance radar in the vicinity of
CYXX, GPS data from the Garmin Aera 696 installed on the aircraft and airport surveillance closed-circuit
television (CCTV) cameras. The radar and GPS data made it possible to obtain information about the aircraft's
flight profile. The CCTV information was helpful in establishing how long the aircraft was exposed to snow prior
to take-off.

The investigation determined that lift-off occurred between 100 and 110 kt indicated airspeed (KIAS). The
published rotation speed specified in the aircraft flight manual for a normal take-off (i.e., with flaps at 0 degrees) is
97 kt KIAS, making the estimated lift-off speed consistent with the rotation speed in the aircraft flight manual. The
airspeed peaked at about 110 KIAS approximately 10 seconds after the aircraft became airborne. The airspeed then
decreased until the aircraft struck the ground at about 100 kt KIAS. Assuming that deceleration was constant, the
aircraft skidded for approximately eight to nine seconds before coming to a full stop.

The investigation determined that the aircraft took off approximately 3 300 ft down the runway, and the airborne
portion of the flight was approximately 3 500 ft. Approximately 2 800 ft of runway remained beyond the impact
point.

According to the aircraft flight manual, the aircraft should achieve rotation airspeed in about 1 700 ft. An analysis
of the available information suggests that a gradual application of power, combined with the increased rolling
resistance on the contaminated runway, resulted in a longer take-off roll. Once the aircraft lifted off, the aircraft's
acceleration decreased for the remainder of the flight.

The last valid altitude point was from radar about eight seconds before impact. Impact analysis conducted by the
TSB estimated the vertical speed at impact was 1 200 ft per minute. The vertical speed and airspeed at impact yield
a final flight path angle of −6.8°. The radar, GPS and impact trajectory provided a complete height profile for the
flight. The peak climb rate was about 1 000 ft per minute and fell to zero within five seconds of take-off as the
altitude reached maximum height. The maximum height was about 100 ft above the runway; however, the aircraft

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may have been as low as 75 ft given the accuracy of Mode S transponder altitude.3 Altitude then decreased until the
impact (Figure 3).

Figure 3: Reconstruction of the path taken by the occurrence aircraft

Note: The “Model” line represents the predicted runway performance based on the aircraft flight
manual, aircraft loading and environmental considerations. (Source: TSB)
Cold temperatures and snow contamination
The aircraft's exterior surface is primarily aluminum, which has a high thermal conductivity and therefore cools
quickly. Some aircraft surfaces will quickly cool to 0°C when exiting warm hangars into sub-zero air, generally
within a few minutes. Although the fuel tanks in the wings may have contained warm fuel, it has been established
that warm fuel in the wings will not prevent all aircraft surfaces from reaching freezing levels. In addition, several
locations on the aircraft (e.g., leading edges, wingtips, ailerons, flaps, empennage) do not contain fuel and, therefore,
would cool at different rates than parts of the aircraft that contain fuel.

Cooling tests were conducted at the TSB Engineering Laboratory with an exemplar aircraft component of typical
lightweight aluminum, taken from indoor temperatures at 20°C to outdoors at -5°C. The initial cooling was rapid,
as much as 10°C per minute. As the temperature of the component dropped, the cooling rate slowed, and the
component reached a temperature of 0°C after about seven minutes of exposure.

3
Mode S transponder altitude is given in 25-ft increments.

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 ASL 3/2024

Figure 4: Cooling test showing melted flakes and ice crystals

Figure 5: Cooling test (close-up)

In the cooling tests, the first snowflakes that fell on the warm component melted into small water drops about
1 to 2 mm in size. As the surface quickly cooled, the melt rate decreased, and a mixture of water drops and partially
melted flakes was observed (Figure 4). As the surface reached 0°C, ice crystals began to grow from the water drops
(Figure 5).

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 ASL 3/2024

As snowfall continued, the falling flakes bonded with the partially melted and re-frozen precipitation layer, creating
a very rough surface that protruded up to 3 mm and was difficult to see on the white paint
(Figure 6). The contamination layer was resistant to attempts to disturb it with airflow or rapid acceleration,
suggesting that it would remain bonded to the surface during a take-off. Some of the contamination seen on the
wreckage after the crash demonstrated this melt/refreeze process and likely existed to some extent before the crash
(Figure 7).

Figure 6: Cooling test after additional snowfall

Figure 7: Occurrence wreckage demonstrating the melt/re-freeze process

approximately 8 hours after the occurrence

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De-icing capabilities at Island Express Air Inc.

At the time of the occurrence, Type 1 de-icing fluid was available at the company.

Ground icing
Snow and ice adhering to the aircraft can have a profound impact on aircraft performance. For that reason, Canadian
Aviation Regulations (CARs) states that “no person shall conduct or attempt to conduct a take-off in an aircraft that
has frost, ice or snow adhering to any of its critical surfaces”4 —a condition known as ground icing. The CARs also
state that “where conditions are such that frost, ice or snow may reasonably be expected to adhere to the aircraft,”
and the aircraft is not operated under Subpart 5 of Part VII or subject to an operator's established aircraft inspection
program, it must be inspected “immediately prior to take-off to determine whether any frost, ice or snow is adhering
to any of its critical surfaces.”

Standard 622.11 of the CARs, Ground Icing Operations, identifies two types of inspections: a critical surface
inspection and a pre-take-off contamination inspection.

The critical surface inspection is a pre-flight external inspection and is mandatory when ground icing conditions
are present. In situations where holdover time is being used as a decision-making criterion, if the holdover time has
been exceeded, take-off can occur only if a pre-take-off contamination inspection is completed or the aircraft is
de-iced or anti-iced again.

The pre-take-off contamination inspection does not require a tactile examination when the manufacturer has
identified representative aircraft surfaces that can be reliably observed during day and night operations to judge
whether critical surfaces are contaminated or not. Of note, the manufacturer has not identified a “representative
aircraft surface” that can be used in lieu of a tactile inspection to visually carry out the pre-take-off contamination
inspection.

If snow and ice are not removed before take-off, they can alter the airfoil contours of the wing to the point where
the lift qualities of the airfoil contours will be seriously impaired due to increased drag and in some cases weight.
This can create control problems, reduce the angle of attack at which the aircraft stalls, decrease rate of climb and
speed performance and increase stall speeds. Even almost imperceptible amounts of ice can cause performance
penalties comparable to much larger, easily visible ice accumulations. Therefore, pilots relying solely on a visual
inspection may not fully appreciate the risk that exists. It is nearly impossible to determine by visual inspection
alone if a wing is wet or has a thin film of ice. This concern is echoed in the TC Aeronautical Information
Manual (TC AIM) and states that “misconceptions exist regarding the effect on performance of frost, snow or ice
accumulation on aircraft.” According to TC's Technical Publication (TP) 10643, “test data indicates that during
take-off, frost, ice or snow formations having a thickness and surface roughness similar to medium or coarse
sandpaper, on the leading edge and upper surface of a wing, can reduce wing lift by as much as 30% and increase
drag by 40%.”

Similarly, other studies have determined that as little as 1/16 inch of icing can increase stall speed by around 20%.
For these reasons, ground icing presents a significant risk, particularly during the take-off phase when the aircraft

4
Canadian Aviation Regulations, section 602.11. This provision states that “critical surfaces” are the wings, control
surfaces, rotors, propellers, horizontal stabilizers, vertical stabilizers or any other stabilizing surface of an aircraft and,
in the case of an aircraft that has rear-mounted engines, includes the upper surface of its fuselage.

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is operating extremely close to its stall speed, and there is much less altitude for recovery should a stall occur shortly
after take-off.

Environmental conditions associated with icing

According to the aircraft flight manual, potential icing conditions exist whenever visible moisture is present and
the outside air temperature is at or below 5°C.

In-flight icing research has identified that severe icing is most likely to occur in conditions of high liquid water
content (e.g., freezing drizzle or freezing rain; mixing icing conditions; or heavy snow) and temperatures below
freezing. Any time that water droplets are visible, it is an indication of high liquid water content. According to the
National Aeronautics and Space Administration (NASA), “snowfall at near-freezing temperatures, roughly -2°C to
+2°C, is likely to have very high moisture content and can stick to your airframe. It is unlikely to ‘blow off’ during
the take-off roll.”

Initially, the ice forms as a thin, rough layer and it will continue to build up, taking on a new shape that can
significantly degrade the aerodynamics of the airframe.

Impact of icing on aircraft performance

Although icing will increase drag, the increase in drag will not be significant during the initial stages of the
take-off roll. As a result, the effects of ground icing may not be noticeable on the aircraft's initial acceleration,
unless the accumulation of ice has significantly increased the aircraft's weight. However, as the aircraft accelerates,
even virtually imperceptible amounts of ice on a wing's upper surface can significantly reduce performance and
make it difficult to rotate and climb away safely.

If the aircraft is able to get airborne, it may initially benefit from the effects of ground effect and gain a small
amount of altitude. This is because a wing in ground effect will have a lower coefficient of drag and a higher
coefficient of lift for any angle of attack, because the wing is considerably more efficient. However, the benefits of
ground effect vanish when the aircraft's height is approximately equal to its wingspan.5 If the wing is contaminated,
increased drag will adversely impact the aircraft's ability to continue the initial climb normally. If the pilot is
unaware of the contamination, they may not realize how close the aircraft's angle of attack is to the stall point. In
addition, stall characteristics with icing can differ significantly from stall characteristics without icing. The aircraft
flight manual states that unusual roll response or uncommanded roll control movements are warnings of an
impending stall.

Aircraft exiting hangars in falling snow

Although a hangar can be used to protect an aircraft from environmental conditions such as snow and/or freezing
precipitation, there are some important considerations for pilots and air operators when bringing an aircraft out of
a hangar into falling snow. The aircraft flight manual states that a plane that has been stored in a hangar should be
treated with anti-icing solution, because snow falling on a relatively warm surface in ambient temperatures that are
below freezing will tend to melt and then re-freeze. If precipitation is present, a warm aircraft should be allowed
sufficient time for the skin temperature to drop below freezing before it is removed from the hangar. The

5
The occurrence aircraft’s wingspan is approximately 46 ft.

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 ASL 3/2024

temperature is typically caused to drop by opening the hangar doors and cold-soaking the aircraft some time before
subjecting the aircraft to direct precipitation.

Continuation bias
To make decisions effectively, a pilot needs an accurate understanding of the situation and an appreciation of the
implications of the situation, then to formulate a plan and contingencies, and to implement the best course of action.
Equally important is a pilot's ability to recognize changes in the situation and to reinitiate the decision-making
process to ensure that changes are accounted for and that plans are modified accordingly. If the potential
implications of the situation are not adequately considered during the decision-making process, there is an increased
risk that the decision and its associated action will result in an adverse outcome that leads to an undesired aircraft
state.

A number of different factors can adversely impact a pilot's decision-making process. For example, increased
workload can adversely impact a pilot's ability to perceive and evaluate cues from the environment and may result
in attentional narrowing. In many cases, this attentional narrowing can lead to confirmation bias, which causes
people to seek out cues that support the desired course of action, to the possible exclusion of critical cues that may
support an alternate, less desirable hypothesis. The danger this presents is that potentially serious outcomes may
not be given the appropriate level of consideration when attempting to determine the best possible course of action.

One specific form of confirmation bias is (plan) continuation bias or plan continuation error. Continuation bias is
best described as “the unconscious cognitive bias to continue with the original plan in spite of changing conditions”
or “a deep-rooted tendency of individuals to continue their original plan of action even when changing
circumstances require a new plan.” Once a plan is made and committed to, it becomes increasingly difficult for
stimuli or conditions in the environment to be recognized as necessitating a change to the plan. Often, as workload
increases, the stimuli or conditions will appear obvious to people external to the situation; however, it can be very
difficult for a pilot caught up in the plan to recognize the saliency of the cues and the need to alter the plan.

When continuation bias interferes with the pilot's ability to detect important cues, or if the pilot fails to recognize
the implications of those cues, breakdowns in situational awareness (SA) occur. These breakdowns in SA can result
in non-optimal decisions being made, which could compromise safety.

In a NASA and Ames Research Center review of 37 accidents investigated by the U.S. National Transportation
Safety Board, it was determined that almost 75% of the tactical decision errors involved in the 37 accidents were
related to decisions to continue on the original plan of action despite the presence of cues suggesting an alternative
course of action. Dekker (2006) suggests that continuation bias occurs when the cues used to formulate the initial
plan are considered to be very strong. For example, if the plan seems like a great plan based on the information
available at the time, subsequent cues that indicate otherwise may not be viewed in an equal light, in terms of
decision-making.

Therefore, it is important to realize that continuation bias can occur, and it is important for pilots to remain cognizant
of the risks of not carefully analyzing changes in the situation and, considering the implications of those changes,
to determine whether or not a more appropriate revised course of action is appropriate. As workload increases,
particularly in a single-pilot scenario, less and less mental capacity is available to process these changes and to
consider the potential impact that they may have on the original plan.

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 ASL 3/2024

Analysis
Nothing was found to indicate that any type of pre-existing or in-flight system malfunction played a role in this
occurrence. As a result, the analysis will focus on the operational aspects of the flight leading up to the accident.

Aerodynamic stall on take-off

As the aircraft took off from the runway and the landing gear was retracted, the aircraft immediately banked to the
left. Although this left bank was initially perceived as a power loss on the left-hand engine, nothing was found to
support this theory. Based on a performance analysis, it is evident that the aircraft did not gain much altitude or
airspeed on take-off. When the aircraft took off, its indicated airspeed reached a peak of approximately 110 kt, and
then began to decrease. This relatively low speed went undetected, as the pilot's attention was primarily outside for
the departure in low visibility conditions.

Based on the combination of environmental conditions and the aircraft's flight profile, it is likely that the aircraft
experienced an aerodynamic stall, as a result of icing and reduced airspeed during the initial climb, once the aircraft
lost the benefits of ground effect. The combination of a warm aircraft surface (i.e., the wings) being exposed to
14 minutes of heavy (wet) snow, in below-freezing temperatures, created a situation that produced conditions highly
conducive to ground icing. The fact that the aircraft was above the maximum allowable take-off weight exacerbated
the situation by increasing the aircraft's stall speed.

As the aircraft climbed out of ground effect on take-off, it experienced an aerodynamic stall as a result of wing
contamination. Pushing the control column forward and landing straight ahead following the unexpected left bank
reduced the aircraft's angle of attack and likely resulted in a partial recovery from the aerodynamic stall before
impact.

Ground icing
The occurrence aircraft, which had been sitting in a warm hangar, was exposed to heavy snow in below-freezing
temperatures for approximately 14 minutes. This created an ideal situation for ground icing to occur.

As the surface temperature of the aircraft reached 0°C, the liquid water portion of the precipitation layer on the
wing would have begun to freeze into ice. The precipitation layer would then include ice from frozen water droplets
and partially melted snowflakes. New snowflakes would continue to bond to the existing layer. The resulting
surface, from the 4 to 5 mm of wet snow that fell on the aircraft, would be very rough and would cause very high
aerodynamic degradation.

No contamination was observed on the aircraft's wings before take-off. However, there may not have been obvious
signs that the wings were contaminated, because it is difficult to visually detect whether a wing is wet or has a thin
film of ice adhering to the surface under visible water droplets.

Although no de-icing fluid had been applied to the occurrence aircraft, the conditions present on that day exceeded
the capabilities of all types of de-icing or anti-icing fluid in heavy snow. The occurrence aircraft exited a warm
hangar and was exposed to 14 minutes of heavy snow in below-freezing conditions. This resulted in a condition
highly conducive to severe ground icing.

Pilot decision-making
In this occurrence, the pilot was motivated to complete this flight with his family, and even though there were a
number of indications that a different course of action may have been warranted, the pilot elected to continue with

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the original plan. On the morning of the occurrence, the telephone conversations with Abbotsford ATC indicated
that the pilot was concerned about the heavy snow and the potential implications of any delays getting airborne.
Having recognized these issues, the pilot did not alter the plan even though the aircraft had spent 14 minutes in
heavy snow at temperatures that presented a significant risk of ground icing. The pilot's decision making was
affected by continuation bias, which resulted in the pilot attempting a take-off with an aircraft contaminated with
ice and snow adhering to its critical surfaces.

Flight planning and pre-flight duties

On the morning of the occurrence, the pilot was involved in several different operational and business-related
activities that diverted his focus away from duties necessary to ensure that the occurrence flight was conducted
safely and in accordance with the CARs. The operational flight plan did not reflect the intended routing, fuel
requirements, or weight and balance.

In addition, because the passengers loaded all the baggage without supervision, the weight of the baggage had not
been confirmed and had not been properly secured. A thorough pre-flight inspection to ensure proper aircraft
loading was not completed. The journey log was not subject to a careful review, and therefore it was not identified
that the aircraft was not airworthy at the time of the occurrence as a result of an incomplete airworthiness directive.

As seen in this occurrence, if pilots do not ensure that flight planning is accurate and that pre-flight duties are
completed, there is an increased risk of operational or technical errors that could jeopardize safety.

Aircraft loading
In this occurrence, the aircraft had a full fuel load, nine passengers on board, and approximately 480 lbs of baggage
in the rear baggage compartment. Although the weight and balance indicated on the operational flight plan showed
the aircraft to be within the aircraft's weight and balance and centre-of-gravity limits, the investigation determined
that the weight and balance information did not accurately reflect the aircraft's true loading. A thorough review of
the aircraft's fuel and the weight of the occupants determined that the aircraft was approximately 200 lbs above the
maximum allowable gross take-off weight. In addition, the aircraft's aft centre of gravity was near its aft limit and
may have made the aircraft more difficult to control as it approached aerodynamic stall. The combination of
operating above the maximum allowable gross weight, near its aft centre of gravity limit, would have increased the
aircraft stall speed and contributed to the instability of the aircraft during the take-off.

The 480 lbs of baggage in the rear baggage compartment was 70 lbs above the maximum allowable weight for the
compartment. The baggage was not weighed before it was loaded on board, and it was loaded by the passengers.
The baggage was secured by a cargo net that came with the aircraft when it was imported into Canada. It could not
be determined whether the cargo net was an approved cargo net. During the impact sequence, the cargo restraint
system used to secure the baggage in the rear baggage compartment failed, causing some of the baggage to injure
passengers seated in the rear of the aircraft cabin.

Snowfall intensity reporting and anti-icing

According to the aviation weather report current at the time of the occurrence, the aircraft departed in moderate
snowfall. However, according to internationally recognized de-icing and anti-icing fluid holdover guidelines, which
were developed based on a more comprehensive understanding of the risks associated with ground icing, the
snowfall intensity would be considered heavy snow. For the purposes of calculating holdover time, heavy snow is
treated in the same manner as ice pellets, moderate and heavy freezing rain, small hail and hail. For these weather
conditions, the holdover time is zero minutes, regardless of the anti-icing fluid type. In other words, anti-icing fluid

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 ASL 3/2024

is considered to no longer be effective in heavy snow conditions as soon as it is applied. This highlights the severity
of heavy snowfall conditions from a ground icing standpoint.

As a result of the difference in meaning of snowfall intensity between aviation weather reports and holdover time
guidelines, it is highly likely that pilots will continue to underestimate the significance of the ground icing risk. If
pilots rely only on the snowfall intensity reported in aviation routine weather reports or automated terminal
information service broadcasts, they will not correctly determine de-icing and anti-icing holdover times, increasing
the risk of aircraft accidents.

Findings

Findings as to causes and contributing factors

1. The occurrence aircraft exited a warm hangar and was exposed to 14 minutes of heavy
snow in below-freezing conditions. This resulted in a condition highly conducive to
severe ground icing.
2. As the aircraft climbed out of ground effect on take-off, it experienced an aerodynamic
stall as a result of wing contamination.
3. The pilot's decision making was affected by continuation bias, which resulted in the pilot
attempting a take-off with an aircraft contaminated with ice and snow adhering to its
critical surfaces.
4. The pilot and the passenger seated in the right-hand crew seat were not wearing the
available shoulder harnesses. As a result, they sustained serious head injuries during the
impact sequence.
5. During the impact sequence, the cargo restraint system used to secure the baggage in the
rear baggage compartment failed, causing some of the baggage to injure passengers
seated in the rear of the aircraft cabin.

Findings as to risk
1. If pilots do not ensure that flight planning is accurate and that pre-flight duties are
completed, there is an increased risk of operational or technical errors that could
jeopardize safety.
2. If pilots rely only on the snowfall intensity reported in aviation routine weather reports or
automated terminal information service broadcasts, they will not correctly determine de-
icing and anti-icing holdover times, increasing the risk of aircraft accidents.
3. If cargo is not loaded within prescribed weight limits and properly secured, there is a risk
that the cargo will shift or come free in an accident, potentially injuring aircraft
occupants.

Other findings
The aircraft was not airworthy at the time of the occurrence as a result of an incomplete airworthiness directive.

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Submission of Aviation Safety Letter (ASL) articles

Do you have an aviation safety topic you are passionate
about? Do you want to share your expert knowledge with
others? If so, we would love to hear from you!

General information and guidance

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It includes articles that address aviation safety from all
perspectives, such as safety insight derived from accidents
and incidents, as well as safety information tailored to the
needs of all holders of a valid Canadian pilot licence or
permit, to all holders of a valid Canadian aircraft
maintenance engineer (AME) licence and to other
interested individuals within the aviation community.
Credit: iStock
If you are interested in writing an article, please send it by
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Happy Fall
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Civil Aviation Documents Issued Recently

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Document No Issue number Subject

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2024-10-10

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Advisory Circulars (ACs)

Document No Issue number Subject
(R-Revised) (Date issued)
AC 521-010 Issue 01 Airworthiness Directives
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AC 700-024 Issue 04 Required Navigation Performance Authorization Required Approach (RNP

2024-07-02 AR APCH): Special Authorization/Specific Approval and Guidance

AC 700-047 Issue 05 Flight Crew Member Fatigue Management–Prescriptive Regulations

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2024-06-03

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