Supplementary Techniques

Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

Flight Operations Briefing Notes

Supplementary Techniques
Altimeter Setting - Use of Radio Altimeter

I Introduction
Operators with international routes are exposed to different standards in terms of:
• Altitude measurement, using different units (i.e., feet or meters);

• Altitude reference setting (i.e., baro setting), using different units (i.e., hectoPascal
or inch-of-mercury);

• Altitude reference for departure and approach, using QNH or QFE; and,

• Environmental conditions (i.e., rapid atmospheric pressure changes and/or low OAT
operation).

This Flight Operations Briefing Note provides a review and discussion of

the following aspects, highlighting the lessons learned from incidents / accidents
(particularly during approach-and-landing) :

• Barometric-altimeter reference (QNH or QFE);

• Use of different units for altitude measurement and reading (i.e., feet versus
meters) and altimeter setting (i.e., In.Hg versus hPa);

• Setting of baro-altimeter bugs (as applicable) and radio-altimeter DH;

• Radio-altimeter callouts; and,

• Low-OAT operation.

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 Supplementary Techniques
Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

II Statistical Data
Deviations from the intended vertical flight profile, caused by omission of an action or
by an incorrect action (including errors in setting the altimeter reference),
are frequently observed during line operation.
The lack of situational awareness, particularly the lack of vertical situational awareness,
is a causal factor in 50 % of approach-and-landing accidents (this includes most
accidents involving a CFIT) (Source: FSF Flight Safety Digest Volume 17 & 18 – November 1998 / February
1999).

III QNH or QFE ?

Some operators set the altimeter to QFE, for takeoff and approach-and-landing, in
areas of operation where the ATC and the majority of other operators use QNH.
This requires adequate SOPs for altimeter-setting and for conversion of assigned
altitudes into heights.

The difference between the QNH and QFE is indicated in approach area chart, e.g. :
• LFBO ( Toulouse Blagnac ) :

− “ ELEV 499 ft / 152 m (18 hPa) ” :

− QNH 1014 hPa QFE = 996 hPa,

− 3000 ft QNH = 2500 ft QFE.

Pilots should be also aware of possible exceptions, such as airports operating with
“QFE only” in a country where QNH is used (such exceptions are indicated on
the applicable approach chart).

Aircraft fitted with electronic flight instrument systems (EFIS) may be capable of using
either QNH / QFE or QNH-only.

IV Altimeter-setting Units
Operators with international routes are exposed to the use of different altimeter setting
units:

• Hectopascals (hPa), previously referred to as milibars (mb);

• Inches-of-mercury (in. Hg); or,

• Milimeters-of-mercury (mm.Hg), on earlier eastern-built aircraft.

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

When in.Hg is used for altimeter setting, unusual barometric pressures such as:

• 28.XX in.Hg (i.e., an unusually low pressure); or,

• 30.XX in.Hg (i.e., an unusually high pressure),

may go undetected when listening to the ATIS or ATC transmissions, resulting in

a more usual 29.XX altimeter setting being set.

A 1.00 in.Hg discrepancy in the altimeter setting results in a 1000-ft error in

the intended (actual) altitude, as illustrated by Figure 1.
Note
Figure 1, Figure 2 and Figure 3 assume :

• a 2000 ft airfield elevation; and,

• a 4000 ft indicated altitude.

In Figure 1, the actual QNH is an unusually low 28.XX in.Hg but the altimeter setting
was mistakenly set to a more usual 29.XX in.Hg, resulting in the actual altitude / height
being 1000 ft lower than indicated:

Actual height
1000 ft AFL

Indicated altitude Actual altitude

4000 ft 3000 ft Field elevation
2000 ft

QNH 28.XX in.Hg Sea level Altimeter error

1000 ft
Altimeter setting 29.XX in.Hg

Figure 1
Effect of a 1.00 in.Hg Too-High Altimeter Setting

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 Supplementary Techniques
Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

In Figure 2, the actual QNH is an unusually high 30.XX in.Hg but the altimeter setting
was mistakenly set to a more usual 29.XX in.Hg, resulting in the actual altitude / height
being 1000 ft higher than indicated.

Actual height
Indicated altitude 3000 ft AFL
4000 ft
Actual altitude
5000 ft
Field elevation
Altimeter setting 29.XX in.Hg 2000 ft

QNH 30.XX in.Hg Sea level Altimeter error

1000 ft

Figure 2
Effect of a 1.00 in.Hg Too-Low Altimeter Setting

Similarly, a 10 hPa error in the altimeter setting would result in a 300 ft error in
the actual altitude (i.e., with a 10 hPa too high altimeter setting, flying at a 4000 ft
indicated altitude would result flying at a 3700 ft actual altitude).

Confusion between altimeter setting units (i.e. hPa versus in.Hg) leads to similar errors
in the actual altitude and actual height above airfield elevation.

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

In Figure 3, an actual QNH of 991 hPa was mistakenly set on the altimeter as 29.91
in.Hg (equivalent to 1012 hPa), resulting in the actual altitude / height being 640 ft
lower than indicated.

Actual height
1360 ft AFL

Indicated altitude Actual altitude

4000 ft 3360 ft
Field elevation
2000 ft

QNH 991 hPa Sea level Altimeter error

640 ft
Altimeter setting 29.91 in.Hg ( 1012 hPa )

Figure 3
Effect of an Altimeter Setting in in.Hg Instead of hPa

V Setting the Altimeter Reference

In order to eliminate or reduce the risk associated with the use of different altimeter-
setting units or with the use of unusual (low or high) altimeter-setting values,
the following rules should be used by controllers (when recording the ATIS message or
when transmitting the altimeter-setting) and by pilots (when reading back
the altimeter-setting):

• All numbers as well as the unit used for the measurement of the atmospheric
pressure (e.g., inches or hectoPascals, sometimes abbreviated as “hex”) should be
indicated in the ATIS’ or air traffic controller’s transmission.

For example, an abbreviated transmission, by the air traffic controller, such as

“altimeter setting six seven” can be interpreted by the pilots as 28.67, 29.67 or
30.67 in.Hg, or as 967 hPa.

Accurately indicating both the altimeter-setting unit and the full value of
the altimeter setting will prevent confusion or enable the detection and correction of
an altimeter-setting error.
• When using inches of mercury (in.Hg), “low” should precede an altimeter setting of
28.XX in.Hg and “high” should precede an altimeter setting of 30.XX in.Hg.
The U.S. FAA accepts this practice, if deemed desirable by regional or local air
traffic services.

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 Supplementary Techniques
Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

VI Use of Metric Altitudes

Using metric altitudes in certain countries (such as the Russian Federation,
the Commonwealth of Independent States [CIS] and the People’s Republic of China)
also requires the use of :
• Metric altimeters; or,

• Conversion tables (i.e., to convert published or assigned altitudes expressed in

meters into feet, for setting a target altitude in the FCU ALT window or for reading
the altimeter).

VII Changing the Altimeter Setting in Climb or Descent

The transition altitude / level is the altitude / level :
• Above which all aircraft are flying with the altimeter-setting (baro setting) set to
the standard (STD) reference (i.e., 1013 hPa / 29.92 In.Hg), and,

• Below which all aircraft are flying with the altimeter-setting set to QNH or QFE.

The transition altitude / level ensure that all aircraft flying within the same airspace fly
with the same altimeter reference.

The transition altitude / level can be either:

• Fixed for the whole country (e.g. 18000 ft / FL 180 in the USA); or,

• Variable, depending on QNH (as indicated in the ATIS message), e.g. :

− LFBO ( Toulouse Blagnac ) approach charts :

− “ TRANS ALT : 5000’ ”,

− “ TRANS LEVEL : BY ATC ”.

Depending on the airline’s / flight crew’s usual area of operation, changing from fixed
transition altitude / level to variable transition level may cause crew confusion and
result in a premature or late setting of the altimeter reference.

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 Supplementary Techniques
Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

VIII Setting of Barometric-altimeter MDA / DA and Radio-altimeter DH

The barometric-altimeter MDA / DA or the radio-altimeter DH should be set in line with
Airbus’ SOPs or company’s SOPs.

Approach Baro Altimeter Radio Altimeter

Visual

Non Precision Approach MDA(H) or DA(H)

( Non-ILS Approach ) Note 2

RNP RNAV Approach DA(H)

ILS CAT I DA(H)

ILS CAT II
DH
ILS CAT III with DH

ILS CAT III with no DH Note 1

Table 1
Use Barometric Altimeter MDA(H)/DA(H) and Radio Altimeter DH

Note 1
DH set to “- 5 ft” for A300/A310/A300-600 families, “NO” entered on PERF APPR page
for other Airbus aircraft families.
Note 2
DA(H), for constant-angle / constant-slope non-precision approaches, as allowed by
operational authorities.

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 Supplementary Techniques
Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

IX Radio-altimeter Callouts
Radio-altimeter callouts can be either:

• Announced (verbalized) by the PNF or the Flight Engineer; or,

• Automatically generated by a synthesized voice (e.g., smart callouts).

Callouts should be tailored to the airline’ operating policy and to the type of approach.

To enhance the flight crew’s terrain awareness, a callout “Radio altimeter alive”,
should be announced by the first crewmember observing the radio altimeter activation
at 2500 ft height AGL.
The radio altimeter reading should then be included in the instrument scanning for
the remainder of the approach.

Radio altimeter readings (i.e., feet’s AGL) below the Minimum Obstacle Clearance
(MOC) values listed below, should alert the flight crew (sources – ICAO-PANS-OPS and
US TERPS):

• Initial approach segment (i.e., from IAF to IF) :

− 1000 ft;

• Intermediate approach segment (i.e., from IF to FAF) :

− 500 ft; and,

• Final approach segment (i.e., after FAF, for non-precision approaches with a defined
FAF, until visual references or reaching MAP) :
− 250 ft.

Unless the airport features high close-in terrain, the radio-altimeter reading (i.e., height
AGL) should reasonably agree with the height above airfield elevation (i.e., height AFE),
obtained by :
• Direct reading of the altimeter, if using QFE; or,

• By subtracting the airport elevation from the altitude reading, if using QNH.

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

X Low OAT Operation

In a standard atmosphere, the indicated altitude (with altimeter set to QNH) provides
the true altitude above the Mean Sea Level (MSL) and, therefore, a reliable indication of
terrain clearance.
Whenever, the temperature deviates significantly from the standard temperature,
the indicated altitude correspondingly deviates from the true altitude (Figure 4) :

• Extreme high temperature :

− the true altitude is higher than the indicated altitude,

• Extreme low temperature :

− the true altitude is lower than the indicated altitude (i.e., 1520 ft true altitude
for a 2000 ft indicated altitude, with a – 40° C OAT), thus resulting in
a lower-than-anticipated terrain separation and a potential obstacle-clearance
hazard.

True altitude

Given atmospheric pressure

( pressure altitude )

Indicated
altitude

3000 ft
2000 ft
1520 ft 2000 ft

1000 ft

High OAT Standard OAT Low OAT

Figure 4
Effect of OAT on True Altitude

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

As a consequence, when performing an ILS approach – for example - with a published

2000 ft glide-slope interception-altitude and a – 40° C OAT, the glide-slope interception
altitude (i.e., altitude selected on FCU) should be increased by 480 ft
(refer to the example shown on Table 2).

The ICAO PANS-OPS, Volume I, provides corrections to be added to the published

minimum safe altitudes (if using QNH) / heights (if using QFE).

The temperature correction to be added to the indicated altitude (height) is a function

of the aerodrome surface temperature (OAT) and of the desired true altitude (height)
above the elevation of the altimeter-setting source, as illustrated by Table 2.

( Source – ICAO PANS-OPS )

Table 2
Low OAT Correction (ft) to be Added to Published Altitudes / Heights

Flying into a low temperature area has the same effect as flying into a low-pressure
area; the aircraft is lower than the altimeter indicates.

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

These effects are summarized and illustrated in Table 3, featuring a well-known

aviation golden rule “ Look Out Below ! ” :

From To Effect on Altitude

Atmospheric Pressure High Low True altitude

is lower than

OAT Warm Cold indicated altitude !

Table 3
The Golden Rule of Altitude Awareness

In most countries, the pilot is responsible for performing the low-OAT correction, except
when under radar control in a radar vectoring area; in this case, the controller normally
is responsible for terrain clearance, including accounting for the cold temperature
correction (when issuing altitude instructions).
Nevertheless, the operator and/or pilot should confirm this responsibility with the air
traffic services of the country of operation.

The temperature correction on altitude affects the following published altitudes, which
therefore should be increased under low OAT operation:
• MEA;
• Airport sector MSA;
• SID / STAR / Approach segments minimum safe altitude;
• SID / STAR altitude constraints;
• Procedure turn / holding minimum altitude;
• FAF altitude;
• Step-down altitude(s) during a non-precision approach;
• MDA(H) during a non-precision (non-ILS) approach;
• DA(H) during a CAT I ILS approach; and,
• OM crossing altitude during any ILS approach (for altitude check purposes).

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

For RNAV approaches conducted with Baro-VNAV vertical profile navigation,

the minimum published altitudes take into consideration (for recent RNAV procedures
only) the effect of low OAT down to a minimum indicated on the approach chart.

As it is not allowed to modify manually the altitude constraints of the FMS vertical flight
plan, the use of Baro-VNAV procedures is not permitted when the aerodrome
temperature is lower than the published lowest temperature for the procedure (Source:
PANS-OPS and TERPS) .

Note
However, a conventional RNAV approach (i.e., LNAV only) is permitted below
this temperature if :
• A corresponding RNAV procedure (i.e. LNAV only) and corresponding MDA(H) is
published; and,
• The appropriate low-temperature correction is applied to all published altitudes
(heights), by the pilot.

ICAO PANS-OPS does not provide altitude corrections for extreme high temperatures.

Note
When operating under extreme high temperature, the temperature effect on the true
altitude may result in a steeper-than-anticipated flight-path angle / vertical speed when
performing a constant-angle non-precision approach.

XI Operational and Human Factors Involved in Altimeter-setting Errors

The incorrect setting of the altimeter reference often is the result of one or more of
the following factors:
• High workload;
• Deviation from normal task sharing;
• Interruptions and distractions; and,
• Absence of effective cross-check and backup between crewmembers.

The analysis of incident / accident reports identify the following operational and human
factors as causes of or contributing factors to altimeter-setting errors :

• Incomplete briefings (i.e., failure to discuss the applicable altimeter-setting unit and
the country practice for fixed or variable transitions altitudes / levels);
• Workload during descent / approach;
• Distraction / interruption;

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

• Language difficulties (unfamiliar accents, speaking pace, unclear contraction of

words, mixed English / local language communications, …);
• Failure to cross-check altimeter-setting information (e.g., ATIS versus TWR
messages, PF / PNF cross-check);
• Fatigue;
• Confusion between altimeter-setting units (i.e., in.Hg or hPa);
• Excessive number of instructions given by ATC in a single message;
• Confusion between numbers such as 5 and 9 (i.e., if 9 is pronounced as nine
instead of niner); and/or,
• Incorrect listening associated with ineffective readback / hearback loop (refer to
Flight Operations Briefing Note on Effective Pilot / Controller Communications).

XII Company Prevention Strategies and Personal Lines-of-Defense

Adherence to the defined task sharing (for normal or abnormal / emergency conditions)
and the use of normal checklists are the most effective lines-of-defense against
altimeter-setting errors.
Altimeter-setting errors often result in a lack of vertical situational awareness;
the following key points should be considered by pilots to minimize altimeter-setting
errors and to optimize the setting of the barometric-altimeter MDA(H) / DA(H) or
radio-altimeter DH:

• Thorough and effective takeoff and approach / go-around briefing (refer to

the Flight Operations Briefing Note Conducting Effective Briefings);

• Awareness of the altimeter setting unit in use at the destination airport, e.g. :
− LFBO ( Toulouse Blagnac ) approach charts :

− “ Alt Set : hPa ”,

• Awareness of rapid QNH / QFE changes due to prevailing weather conditions

(i.e., extreme cold or warm fronts, steep frontal surfaces, semi-permanent or
seasonal low pressure areas);

• Awareness of the anticipated altimeter setting, using two independent sources for
cross-check (e.g., METAR and ATIS messages);

• Effective PF/PNF crosscheck and backup;

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

• Adherence to SOPs for:

− Sterile-cockpit rule during taxi, takeoff and descent-approach phases;
− Change of barometric-altimeters setting in climb and descent, for example:
• in climb: at the transition altitude; and,
• in descent: when approaching the transition level and when cleared to
an altitude;

− use of standby-altimeter to cross-check main altimeters;

− altitude callouts (e.g., approach-fix crossing altitudes);
− including the radio-altimeter in the instrument scan, when the radio-altimeter is
“alive” (i.e., below 2500 ft RA);
− radio-altimeter callouts; and,
− setting the barometric-altimeter MDA(H) or DA(H) or the radio-altimeter DH.

• Exercising extra vigilance and cross-check if QFE is used for approach and landing.

The following prevention strategies should be considered by air traffic controllers :

• Limiting the number of instructions transmitted in a given message;

• Indicating all the numbers and the unit defining the altimeter setting;

• Adhering to the standard phraseology and pronunciation;

• Adopting the accepted terminology “low” before a 28.XX in.Hg altimeter setting and
“high” before a 30.XX in.Hg altimeter setting.

XIII Associated Flight Operations Briefing Notes

The following Flight Operations Briefing Notes also refer to altimeter-setting and
altitude issues:
• Operating Philosophy – SOPs
• Conducting Effective Briefings
• Effective Pilot / Controller Communications
• Managing Interruptions and Distractions
• Preventing Altitude Deviations

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

XIV Regulatory References

• ICAO Annex 3 – Meteorological Service for International Air navigation, Chapter 4.

• ICAO Annex 5 – Units of Measurement to be used in Air and Ground Operations,

Table 3-4, 3.2.

• ICAO Annex 6 – Operations of Aircraft, Part I – International Commercial Air

transport – Aeroplane, 6.9.1 c) and Appendix 2, 5.13.

• ICAO Annex 6 – Procedures for Air Navigation Services – Rules of the Air and Air
Traffic Services (PANS-RAC, Doc 4444).

• ICAO – Procedures for Air navigation Services – Aircraft Operations (PANS-OPS, Doc
8168), Volume I – Flight procedures - Part VI – Altimeter Setting Procedures -
Chapter 3 :
− New table of temperature corrections to be added to altitude when operating
in low OAT conditions.
The new Part VI – Chapter 3 became effective in Nov.2001 (Amendment 11).

• ICAO - Preparation of an Operations manual ( Doc 9376 ).

• ICAO - Manual of Radiotelephony ( Doc 9432 ).

• ICAO - Human Factors Training Manual ( Doc 9683 ).

• ICAO - Human Factors Digest No.8 – Human Factors in Air Traffic Control
(Circular 241).

• UK CAA – CAP 710 – Level Bust Working Group – “ On The level ” – Final Report

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Flight Operations Briefing Notes Altimeter Setting – Use of Radio Altimeter

XV Industry References
• Eurocontrol - Level Bust website :
− http://www.eurocontrol.int/safety/LevelBust_LevelBust.htm
− Level Bust Tool Kit

• Flight Safety Foundation website – http://www.flightsafety.org

− Flight Safety Digest – November 2004 – RVSM Heightens Need for Precision in
Altitude Measurement

• NASA – ASRS website - http://asrs.arc.nasa.gov/main.htm

− ASRS Directline bulletin – Issue No.2 – Oct.1991 – International Altimetry
− ASRS Directline bulletin – Issue No.9 – Mar.1997 – The Low-Down on Altimeter
Settings

This Flight Operations Briefing Note (FOBN) has been developed by Airbus in the frame of the Approach-and-Landing
Accident Reduction (ALAR) international task force led by the Flight Safety Foundation.

This FOBN is part of a set of Flight Operations Briefing Notes that provide an overview of the applicable standards,
flying techniques and best practices, operational and human factors, suggested company prevention strategies and personal
lines-of-defense related to major threats and hazards to flight operations safety.

This FOBN is intended to enhance the reader's flight safety awareness but it shall not supersede the applicable regulations
and the Airbus or airline's operational documentation; should any deviation appear between this FOBN and the Airbus or
airline’s AFM / (M)MEL / FCOM / QRH / FCTM, the latter shall prevail at all times.

In the interest of aviation safety, this FOBN may be reproduced in whole or in part - in all media - or translated; any use of
this FOBN shall not modify its contents or alter an excerpt from its original context. Any commercial use is strictly excluded.
All uses shall credit Airbus and the Flight Safety Foundation.

Airbus shall have no liability or responsibility for the use of this FOBN, the correctness of the duplication, adaptation or
translation and for the updating and revision of any duplicated version.

Airbus Customer Services

Flight Operations Support and Services

1 Rond Point Maurice Bellonte - 31707 BLAGNAC CEDEX FRANCE

FOBN Reference : FLT_OPS – SUPP_TECH – SEQ 01 – REV 03 – DEC. 2005

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 Supplementary Techniques
Flight Operations Briefing Notes Preventing Altitude Deviations / Level Busts

Flight Operations Briefing Notes

Supplementary Techniques
Preventing Altitude Deviations / Level Busts

I Introduction
Altitude deviations ( also referred to as level busts ) may result in substantial loss of
vertical separation and/or horizontal separation, which could cause a midair collision.
Traffic avoidance maneuvers, if required, usually result in injuries to passengers and
crewmembers ( particularly to cabin attendants ).
This Flight Operations Briefing Note provides an overview of the factors involved in
altitude deviations.
This document can be used for stand-alone reading or as the basis for the development
of an airline’s altitude awareness program.

II Statistical Data
An analysis reveals that (source - U.S. FAA and US Airways) :
• Approximately 70 % of altitude deviations are the result of a breakdown in
the pilot/controller communication loop; and,

• Nearly 40 % of altitude deviation events affect the critical pair constituted by FL 100
/ FL 110 (or 10 000 ft / 11 000 ft).

A study performed by the UK CAA, between 1995 and 1997, showed that 50 % of
altitude deviations take place below 8000 ft, usually as the result of the mis-
understanding of the altitude restrictions applicable during departure (SID) or approach
(STAR).

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Flight Operations Briefing Notes Preventing Altitude Deviations / Level Busts

A survey indicates that, worldwide (source – Eurocontrol) :

• Once every 30 minutes, an aircraft is busting its cleared altitude / flight level; and,

• Each day, a loss of separation results in involved aircraft passing within a mile from
each other.

The distribution of level bust events by flight phase is provided below (source - British
Airways, Eurocontrol and IATA STEADES – rounded figures) :

• Climb : 60 % - mostly caused by late altitude clearances;

• Cruise : 10 % - mostly caused by turbulence / windshear or autopilot operation;

• Descent : 30 %.

III Defining an Altitude Deviation ( Level Bust )

An altitude deviation ( level bust ) is defined by regulations as an unauthorized
deviation from the assigned altitude ( or flight level ) equal to or greater than 300 ft
( 200 ft in RVSM airspace ).
This also includes the failure to capture the assigned altitude / flight level
( i.e., overshoot or undershoot of the cleared altitude / flight level ).

Altitude deviations may result in :

• A loss of separation;
• A midair collision; or,
• A CFIT event.

IV Operational and Human Factors Involved in Altitude Deviations

Altitude deviations always are the result of a breakdown in either:

• The pilot / system interface :
− Altimeter setting, use of autopilot, monitoring of instruments and displays
(e.g., undetected system faults);

• The pilot / controller interface :

− Communication loop; or,

• The PF / PNF interface :

− Task-sharing, call-outs, cross-check and back-up.

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Flight Operations Briefing Notes Preventing Altitude Deviations / Level Busts

Table 1 summarizes and ranks the main operational factors observed in altitude
deviations / level busts.

Operational Factors % of Events

Flight Management / Monitoring 25 - 40

Air Traffic Management / Control 20 - 30

Weather 15 - 20

Auto Flight System 10 – 20

Response to TCAS / ACAS TA or RA 10

Miscellaneous 5 - 10

( Source – UK CAA / Eurocontrol / IATA STEADES – 1997-2004 )

Table 1
Factors in Altitude Deviations / Level Busts

Altitude deviations often occur as the result of one or a combination of the following
conditions, that may involve :

• The flight crew,

• The air traffic controller, or,

• The design of the airspace and terminal area procedures.

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Flight Operations Briefing Notes Preventing Altitude Deviations / Level Busts

Flight Crew

Table 2, below, summarizes and ranks the main Flight Management / Flight Monitoring
factors observed in altitude deviations / level bust events.

Flight Management / Monitoring Factors % of Events

Flight Crew Incorrect Selection

25 - 30
( Altimeter Setting or Selected Altitude / FL )

Use / Supervision of Automation 10 - 15

Manual Flying / Flight Path Monitoring 10 – 15

Weather
5 - 10
( Windshear, Turbulence, Standing Waves )

Adherence to SOPs / Use of Checklists 5 - 10

Response to TCAS / ACAS TA or RA 5 - 10

ATC Service Standard 5

( Source – UK CAA / Eurocontrol / IATA STEADES – 1997-2004 )

Table 2
Flight Management / Monitoring Factors in Altitude Deviations / Level Busts

The following detailed contributing factors are often cited in altitude deviations / level
bust attributed to flight management / flight monitoring by flight crew :

• Unfamiliar airspace and procedures;

• Callsign confusion (refer to Flight Operations Briefing Note on Effective Pilot /

Controller Communications);

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Flight Operations Briefing Notes Preventing Altitude Deviations / Level Busts

• Late selection of altimeter setting (i.e., STD or QNH / QFE);

• Use of an incorrect altimeter setting (i.e., either incorrectly transmitted by ATC or

copied by flight crew), this factor is observed in 10 % of events :
− Refer to the Flight Operations Briefing Note on Altimeter Setting –
Use of Radio Altimeter;

• Interruption or distraction (refer to the Flight Operations Briefing Note on

Managing Interruptions and Distractions);

• Misunderstanding of the assigned altitude;

• Pilot understands and reads back the correct altitude or FL, but select an incorrect
altitude or FL on the FCU, e.g. because of :
− Confusion of numbers with an other element of the controller’s message
(e.g., speed, heading or flight number);
− Expectation / anticipation of another altitude or FL;
− Interruption / distraction; or,
− Breakdown in crew crosscheck and backup;

• Pilot / controller communication breakdown (mainly readback / hearback errors),

e.g.:
− Controller transmits an incorrect altitude, the pilot does not readback and
the controller does not challenge the absence of readback;
− Pilot understands and readback an incorrect altitude but controller does not hear
back and does not correct the crew readback;

• Lack of active flight path monitoring, resulting in :

− Failure to level-off at the assigned altitude; or,
− Failure to reach or maintain the assigned altitude (or altitude restriction) at
the point or time assigned by ATC.

• Pilot or autopilot overshoots / undershoots or fails to capture the selected altitude /

FL (e.g., due to high rate of climb or descent) ;

• Unanticipated ATC request for step-climb or step-descent;

• Unwarranted response to a TCAS (ACAS) TA;

• Response to a TCAS (ACAS) RA;

• Severe windshear (i.e., up-draught / down-draught);

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Flight Operations Briefing Notes Preventing Altitude Deviations / Level Busts

• Absence of response to the altitude alert aural and visual warnings, when in hand
flying; or,

• Incorrect go-around procedure and maneuver.

Air Traffic Controllers

Table 3, below, summarizes and rank the main ATM / ATC factors observed in altitude
deviations / level bust events.

ATM / ATC Factors % of Events

Late Clearance / Re-clearance 50

Complex / Confusing Instructions 20

Inappropriate Vectoring Instructions 10 - 15

Insufficient Separation 5 - 10

Incorrect Coordination Between ATC’s 5 - 10

Response to TCAS / ACAS TA or RA 5 - 10

Miscellaneous 5 - 10

( Source – UK CAA / Eurocontrol / IATA STEADES – 1997-2004 )

Table 3
ATM / ATC Factors in Altitude Deviations / Level Busts

The following detailed contributing factors are often cited in altitude deviations / level
bust attributed to ATM / ATC instructions / services :

• Callsign confusion (refer to Flight Operations Briefing Note on Effective Pilot /

Controller Communications);

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• Interruption or distraction (refer to Flight Operations Briefing Note on Managing

Interruptions and Distractions);

• The controller assigns an incorrect altitude, or reassigns a FL after the aircraft has
been cleared to an altitude;

• Controller English proficiency / use of standard phraseology / speed of transmission;

• Late altitude clearance / re-clearance not achievable without overshoot /

undershoot;

• ATC instruction for an altitude restriction when being above the transition altitude
(i.e., with altimeters set to STD);

• Pilot / controller communication breakdown (mainly readback / hearback errors),

e.g.:
− Controller transmits an incorrect altitude, the pilot does not readback and
the controller does not challenge the absence of readback;
− Pilot understands and readback an incorrect altitude but controller does not hear
back and does not correct the crew readback; or,
− Pilot accepts an altitude clearance intended for another aircraft (confusion of
callsigns);

• Complex ATC transmission containing more than two instructions (e.g., on speed,
altitude and heading);

Design of Airspace and Terminal Area Procedures

The sharing of experience and the joint cooperation between operators and air traffic
control services has enabled the initiation of significant enhancements in terms of air
traffic management and air traffic control, e.g. :

• Vertical and lateral segregation / deconflicting of arrival and departure procedures

to prevent the likelihood of level busts / reduced separations, particularly at sectors’
boundaries; and.

• Design of ATC sectors to minimize the need for step-climb or step-descents.

V Prevention Strategies - Altitude Awareness Program

The development and implementation of altitude awareness programs by several
airlines have reduced significantly the number of altitude deviations.
To address the main causes of altitude deviations, an altitude awareness program
should first assess the company risk exposure and include the following aspects.

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Standard Operating Procedures – Crew Resource Management

An altitude awareness program should enhance the respective roles of the PF and PNF
by stressing the importance of :

• Strict adherence to Standard Operating Procedures (SOP’s) :

− Task sharing for normal and non-normal operations;
− Strict adherence to sterile-cockpit rule; and,
− Briefing techniques that must be resilient to routine !
(refer to Flight Operations Briefing Note on Conducting Effective Briefings).

• Strict adherence to Crew Resource Management (CRM) principles, e.g. :

− Stating (verbalizing) intentions and actions, when they are different from
expectations (e.g., delayed climb or descent, management of altitude or speed
restrictions); and,
− Mutual cross-check and back-up.

Pilot / Controller Communications

Breakdown in the pilot/controller communication loop includes:

• Readback / hearback errors (this risk is greater when one crewmember does not
monitor radio communications because of other duties such as listening to the ATIS
or being involved in company communications or passenger-address
announcements );

• Blocked transmissions; or,

• Confusion of call signs.

The following recommendations (discussed and expanded in the Flight Operations

Briefing Note on Effective Pilot / Controller Communications ) can enhance
communications and raise the level of situational awareness of pilots and controllers :
• Be aware that readback / hearback errors may involve both the pilot and
the controller :
− The pilot may be interrupted or distracted when listening to a clearance, confuse
similar callsigns, forget an element of the instruction or be subject to the bias of
expectation when understanding or when reading back the instruction (this bias
usually is referred to as wish-hearing );

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− The controller may also confuse similar callsigns, be distracted by other radio or
landline telephone communications or be affected by blocked transmissions or
high workload.

• Use standard phraseology for clear and unambiguous pilot / controller and intra-
cockpit communications.
Standard phraseology is the common basis for pilots and controllers; this common
language allows an easier detection and correction of errors.

• Use of an adapted phraseology to increase the controller situational awareness,

e.g.:
− When leaving an altitude, announce:
Leaving […] for […]; or,
Leaving […] and climbing / descending to […];
The call leaving … should be performed only when a vertical speed of 500 ft/mn
has been established and the altimeter positively shows the departure from the
previous altitude or FL;
This recommendation takes a particular importance when descending in
a holding pattern;

− Use of two separate methods for expressing certain altitudes – one one
thousand feet, that is eleven thousand feet; and,
− Preceding each number by the corresponding flight parameter (i.e., FL, heading,
speed), e.g., descend to Flight Level two four zero instead of descend to two
four zero.

• If doubt exists about a clearance, request confirmation from ATC, do not attempt to
guess an instruction or clearance based on flight deck discussion.

Task Prioritization and Task Sharing

The following guidelines and recommendations should be considered for optimum

prioritization of tasks and task sharing:

• Reduce non-essential tasks during climb and descent (in addition to the sterile
cockpit rule, some operators consider the last 1000 ft before reaching any assigned
altitude as a sterile-cockpit period);

• Monitor / supervise the operation of AP for correct level-off at the cleared altitude /
FL and for correct compliance with altitude or time restrictions (constraints);

• Plan tasks that prevent attentive listening to radio communications (such as copying
the ATIS, company calls, and passengers-address announcements) during periods
of lesser ATC communications.

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• When one crewmember cannot monitor the ATC frequency because of other duties
or because leaving the cockpit, the other crewmember should :

− Acknowledge receiving the radio and controls, as applicable;

− Check the radio volume to ensure adequate reception of ATC calls;

− Give an increased attention to listening / confirming / reading back (because of

the momentary absence of backup); and,

− Brief the other crew member when he/she returns, highlighting any relevant new
information and any change in the ATC clearance or instructions.

Altitude-setting Procedures

The following techniques should be considered for enhancing standard operating

procedures (SOPs):

• When receiving an altitude clearance, set the cleared altitude value immediately in
the selected altitude window (even before readback, if deemed more suitable due to
workload);

• Ensure that the altitude selected is cross-checked by both crewmembers (e.g., each
crew member should verbalize what he or she heard and then point to the selected
altitude window to confirm that the correct value has been set);

• Ensure that the cleared altitude is above the sector minimum safe altitude; and,

• When under radar vectoring, be aware of the applicable minimum vectoring altitude
for the sector or positively request confirmation of an altitude clearance that is
below the sector MSA.

Standard Calls - Callouts

Use standard calls to increase the PF / PNF situational awareness, to ensure an effective
backup and challenge, and detect a previous error on the assigned / cleared altitude
or FL :

• Modes changes on FMA and changes of targets on PFD/ND;

• Leaving [...] for […], when a 500 ft/mn vertical speed has been established; and
altimeter indicates departure from the previous altitude; and,

• One thousand below (above) [altitude or FL], when within 1000 ft from
the cleared altitude or FL.

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Note
Although the Airbus SOP’s recommend the use of the above standard call, some
operators use different standard calls such as :
− One to go;
− One thousand to go; or,
− […] for […].

When within 1000 ft from the cleared altitude / FL or from an altitude restriction
(constraint):

• PF should concentrate on instruments scanning (one head in); and,

• PNF should watch outside for traffic, if in VMC (one head out).

Use of Automation

The use of automation with the correct level of automation for the task and
circumstances will assist flight crew in preventing altitude deviations / flight level bust,
in conditions such as :

• Unfamiliar airspace / airport;

• Congested airspace;

• Adverse weather; and / or,

• Flight crew experience (e.g., flight crew including a junior first officer).

Refer to the Flight Operations Briefing Note on Optimum Use of Automation .

VI Flight Level or Altitude Confusion

Confusion between FL 100 and FL 110 (or between 10 000 ft / 11 000 ft) is usually
the result of the combination of two or more of the following factors:

• Readback / hearback error because of similar sounding phrases;

• Non adherence to standard ICAO phraseology;

• Mindset leaning to focus only on “one zero” and thus to more easily understand
“10 000 feet”;

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• Failing to question the unusual (e.g. bias of expectation or routine on a familiar SID
or STAR) and/or,

• Interpreting subconsciously a request to slow down to 250 kt as a clearance to

descend to FL 100.

VII Transition Altitude / Level

As indicated in the Flight Operations Briefing Note on Altimeter Setting – Use of radio
Altimeter, the transition altitude / flight level can be either:

• Fixed for the whole country (e.g. 18 000 ft / FL 180 in the United States); or,

• Transition altitude is defined in the approach charts (e.g., 5000 ft) and transition
level is variable as a function of the QNH (as indicated in the ATIS message).

Depending on the airline’s / flight crew’s usual area of operation, changing from fixed
transition altitudes/FL to variable transition altitudes / FL may result in crew confusion
and in a premature or late change of the altimeter setting.

In countries operating with reference to the QFE, when below the transition altitude or
FL, the readback should indicate the altimeter reference (i.e., QFE).

VIII Altitude Deviations in Holding Patterns

In holding patterns controllers rely on pilots to maintain the assigned altitude or to
descend to the new cleared altitude.
The overlay of aircraft tags on the controller’s radar display does not allow
the immediate detection of an impending traffic conflict.
Controllers, therefore, assume that a correctly readback clearance will be correctly
complied with.
Secondary surveillance radar’s (SSR) provide conflict alerts but no resolution advisory;
accurate and clear pilot / controller communications are essential when descending in
a holding pattern.
Two separate holding patterns may be controlled by the same controller, on the same
frequency.
The following communication rules are, therefore, important when in a holding pattern:
• Do not take a communication intended for an other aircraft (by confusion of similar
callsigns);
• Prevent / minimize the risk of blocked transmission, in case of simultaneous
readback by two aircraft with similar callsigns or simultaneous transmissions by
the pilot and the controller; and,
• Announce leaving [FL or altitude] only when the vertical speed indicator and
the altimeter reflect the departure from the previous altitude.

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IX Summary of Key Points

An altitude awareness program should be emphasized during transition and recurrent
training and during line checks.
Blame-free reporting of altitude deviation events should be encourage to broaden
the understanding of causal and circumstantial factors resulting in altitude deviations.

The following safety key points should be promoted:

• Adhere to the pilot / controller readback / hearback process (communication loop);
• Crosscheck and backup each other to ensure that the altitude selected is the cleared
altitude received;
• Cross-check that the cleared altitude is above the sector minimum safe altitude
(unless crew is aware of the applicable minimum vectoring altitude for the sector);
• Monitor instruments and automation when approaching the cleared altitude or FL;
and,
• In VMC, apply the technique one head inside / one head out when reaching
the cleared altitude or FL.

Altitude deviations can be prevented by strict adherence to adequate SOPs,

this includes correctly :
• Setting the altimeter-reference on barometric altimeters; and,
• Selecting the cleared altitude or FL on the FCU.

The TCAS (ACAS) is an effective safeguard to minimize the consequences of altitude

deviations.

X Associated Flight Operations Briefing Notes

The following Flight Operations Briefing Notes refer to altimeter setting and altitude
issues, and associated procedures :
• Operating Philosophy – SOPs
• Optimum Use of Automation
• Operations Golden Rules
• Standard Calls
• Effective Pilot / Controller Communications
• Managing Interruptions and Distractions
• Altimeter Setting – Use of Radio Altimeter

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XI Regulatory references

• ICAO :
− Annex 6, Parts I, II and III, Sections II and III (amended in 1995) for
discouraging the use of three-pointer and drum-pointer altimeters
− Annex 6, Operation of Aircraft, Part I – International Commercial Air Transport –
Aeroplanes, 4.2.6, 6.9.1 c) and Appendix 2, 5.13, 5.15
− Procedures for Air Navigation Services – Rules of the Air and Air Traffic Services
(PANS-RAC, Doc 4444)
− Procedures for Air Navigation Services – Aircraft Operations (PANS-OPS, Doc
8168), Volume I, Flight Procedures (Post Amendment No 11, applicable 1
November 2001)

• US FARs :
− FAR 91.119 - Minimum Safe Altitude
− FAR 91.121 - Altimeter Setting
− FAR 91.129 - ATC communications
− FAR 91.221 and FAR 121.356 for TCAS installation
− FAR 91 – Appendix G – Operations in Reduced Vertical Separation Minima
(RVSM) airspace

• UK CAA :
− CAP 413 - Required criteria in announcing leaving an altitude or FL
− CAP 710 – Level Bust Working Group – “ On The Level ” project – Final Report –
1999
+
− Data Plus Safety Letter – Level Busts – July 1998
− Level Bust - website - http://www.caa.co.uk/srg/levelbust

XII Industry References

• Flight Safety Foundation website – http://www.flightsafety.org
− Flight Safety Digest – June 1993 – Research Identifies Common Errors Behind
Altitude Deviations
− Flight Safety Digest – December 1995 – Altitude Awareness Programs Can
Reduce Altitude Deviations
− Flight Safety Digest – March 1999 – Enhancing Flight Crew Monitoring Skills

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• Eurocontrol website - http://www.eurocontrol.int/safety/ :

− Level Bust Tool Kit – website :
• http://www.eurocontrol.int/safety/LevelBust_LevelBust.htm

− Level Bust Safety Letters / Bulletins (available on the above Eurocontrol

website):
• Level Bust – A Shared Issue ? – June 2001
• Reducing Level Bust – November 2002
• En Route to Reducing Level Bust – May 2003

− ACAS II – website – http://www.eurocontrol.int/acas/ :

• Safety Letters and Bulletins

• NASA – ASRS website - http://asrs.arc.nasa.gov/main.htm

− ASRS Directline bulletin – Issue No.2 – Oct.1991 – International Altimetry
− ASRS Directline bulletin – Issue No.9 – Mar.1997 – The Low-Down on Altimeter
Settings

• IATA – STEADES - Safety Trend Analysis Report – 2002 and 2004

This Flight Operations Briefing Note (FOBN) has been developed by Airbus in the frame of the Approach-and-Landing Accident
Reduction (ALAR) international task force led by the Flight Safety Foundation.

This FOBN is part of a set of Flight Operations Briefing Notes that provide an overview of the applicable standards,
flying techniques and best practices, operational and human factors, suggested company prevention strategies and personal
lines-of-defense related to major threats and hazards to flight operations safety.

This FOBN is intended to enhance the reader's flight safety awareness but it shall not supersede the applicable regulations
and the Airbus or airline's operational documentation; should any deviation appear between this FOBN and the Airbus or
airline’s AFM / (M)MEL / FCOM / QRH / FCTM, the latter shall prevail at all times.

In the interest of aviation safety, this FOBN may be reproduced in whole or in part - in all media - or translated; any use of
this FOBN shall not modify its contents or alter an excerpt from its original context. Any commercial use is strictly excluded.
All uses shall credit Airbus and the Flight Safety Foundation.

Airbus shall have no liability or responsibility for the use of this FOBN, the correctness of the duplication, adaptation or
translation and for the updating and revision of any duplicated version.

Airbus Customer Services

Flight Operations Support and Services
1 Rond Point Maurice Bellonte - 31707 BLAGNAC CEDEX FRANCE
FOBN Reference : FLT_OPS – SUPP_TECH – SEQ 02 – REV 02 – MAY 2005

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 Supplementary Techniques
Flight Operations Briefing Notes Handling Engine Malfunctions

Flight Operations Briefing Notes

Supplementary Techniques
Handling Engine Malfunctions

I Introduction
The failure rate of aircraft engines has reached an all-time low. This means that many
flight crews will never face an engine failure during their career, other than those in
the flight simulator.
However, simulators are not fully representative of engine failures because
accelerations (e.g. due to a failed engine), noise (e.g. caused by an engine stall), or
vibrations (e.g. in the event of a blade rupture) are hard to simulate.
Consequently, flight crews are not always able to identify and understand engine
malfunctions. Incorrect crew understanding of engine malfunctions can lead to
unnecessary engine shutdowns, but also to incidents and accidents.

The objective of this Flight Operations Briefing Note is to:

• Provide basic guidelines to identify engine malfunctions
• Give typical operational recommendations in case of engine malfunctions.

II Statistics – Background Information

When the jet engine was introduced in civil aviation in the 1950s (de Havilland Comet,
Sud-Aviation Caravelle), the available thrust was less than 10,000 lbs.
Today, high by-pass ratio engines produce up to 115,000 lbs of thrust.

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During the same time, the rate of In-Flight Shut Downs (IFSD) has decreased as
follows:

IFSD (per 100,000 engine FH)

1960s 40

Today Less than 1

(Source: AIA/AECMA Project Report on Propulsion System Malfunction + Inappropriate Crew Response, November 1998)

Figure 1
In-Flight Shut Down Rate

In other words:
• In the 1960s, in average each engine failed once a year
• Today, in average, each engine fails every 30 years.

This improvement in the rate of IFSD has allowed the introduction of ETOPS (Extended
Twin Operations) in 1985. Among other criteria, to be approved for ETOPS 180,
the rate of IFSD must be less than 2 per 100 000 engine flight hours.
This also means that pilots that start their career today will probably never experience
an IFSD due to an engine malfunction.
However, despite the significant improvement in engine reliability, the number of
accidents (per aircraft departure) due to an incorrect crew response following an engine
malfunction has remained constant for many years. This prompted a study with
all major industry actors involved (aircraft and engine manufacturers, authorities,
accident investigation agencies, pilot organizations).

Among the results were:

• The vast majority of engine malfunctions are identified and handled correctly.
However, some malfunctions are harder to identify
• Most crews have little or no experience of real (i.e. not simulated) engine
malfunctions
• Simulators are not fully representative of all malfunctions
• Training does not sufficiently address the characteristics of engine malfunctions.

The following crew undue actions, caused by engine malfunctions, have been observed:
• Loss of control (trajectory not adapted to the engine failure)
• Rejected takeoff above V1

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• Shutdown of the wrong engine

• Unnecessary engine shutdown
• Application of the wrong procedure / Deviation from the published procedure.

III Engine Parameters

III.1 Primary Engine Parameters

The primary engine parameters are permanently displayed on the Engine and Warning
Display (EWD), or on the center panel (A300/A310). These parameters are (Figure 2):
• EPR (Engine Pressure Ratio) and/or N1 (Fan speed) as applicable
• N2 (and N3 for RR engines): High Pressure Compressor rotor speed
• EGT: Exhaust Gas Temperature.

Figure 2
Main Engine Parameters (Rolls-Royce Engine Example)

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EPR / N1
EPR and N1 are both representative of the engine thrust. Consequently, depending on
the engine type, either N1 or EPR is used as the primary thrust parameter (when EPR is
the primary thrust parameter, N1 is used as a backup).

Note:
On the A380, a new parameter called THRUST provides an easy interpretation of
available thrust (0% = windmiling thrust; 100% = TOGA thrust (bleeds off), whatever
the external conditions (temperature and altitude))

A low EPR (or N1) can be the sign of an engine flameout.

Rapidly fluctuating EPR (or N1) can be the sign of an engine stall.

N2 (or N3 for RR engines)

The N2 (or N3 for RR engines) is used to monitor the engine start/relight sequence.
Rapidly fluctuating N2 (or N3) can also be the sign of an engine stall.

EGT
A high EGT can be the sign of:
• An ageing engine
• An engine stall
• A tailpipe fire
• An engine failure.

III.2 Secondary Engine Parameters

The other engine parameters are fuel flow, engine vibrations, oil quantity/temperature/
pressure, and nacelle temperature.
Fuel Flow is usually displayed with the main engine parameters on the EWD or on
the center panel.
The other secondary engine parameters are displayed on the ECAM System Display
(SD), on the center panel, or on the Flight Engineer’s station. These parameters (in
particular oil pressure and temperature) should be monitored throughout the flight,
amongst others, during the periodic cruise check.
On all Airbus aircraft (except the A300 B2/B4), when a parameter drifts out of
its normal range, the Engine SD will be automatically displayed and the parameter will
pulse (in green). This is referred to as an ECAM advisory.

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Flight Operations Briefing Notes Handling Engine Malfunctions

IV Identifying Engine Malfunctions

Most engine malfunctions can be easily identified, thanks to dedicated
warnings/cautions or indications. However, some malfunctions are harder to identify,
and require some flight crew knowledge, in order to properly understand and handle
them.

IV.1 Engine Fire

An engine fire is easy to identify, and is also sometimes referred to as an “external
fire”, or “nacelle fire” because it occurs inside the engine nacelle but out of the engine
core and gas path.
An engine fire can occur at any time, both on ground and in flight.

It is usually due to inflammable fluid coming into contact with very hot engine parts,
such as the compressor, turbine or the combustion chamber casings. This can be
caused by:
• Leaks
• The rupture of a pipe (e.g. caused by the rupture of a rotating part of the engine)
• A damage affecting the accessory gearbox
• The rupture of the combustion chamber, that can lead to a torch flame.

When the inflammable fluid comes into contact with the hot engine parts, the fire will
auto-ignite. These inflammable fluids are:
• Fuel (Auto inflammation at 230°C)
• Oil (Auto inflammation at 260°C)
• Hydraulic Fluid (Auto inflammation at 450°C).

Engine fire detection is based on temperature sensors (loops) located in sensitive areas
around the engine and in the pylon (Figure 3). This location differs for each engine
type, based on the engine’s characteristics.

Figure 3
Typical Fire Detection Sensors (Loops) Location

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The fire detection sensors are on two identical fire detection loops.

When an engine fire is detected, a warning triggers. The procedure requests to:
• Shut down the engine
• Isolate the engine with the ENG FIRE pushbutton/handle (shuts hydraulic,
pneumatic and fuel lines, disconnects electric power)
• Discharge the fire agents.

Note:
The principle of the engine fire detection also means that spurious fire warnings can be
triggered if hot air is blown on the fire detection loops (e.g. hot bleed air duct rupture,
or combustion chamber cracks).

As long as the engine fire is detected, apply the ENG FIRE procedure.

If an engine fire occurs during takeoff or go-around, the PF shall first establish and
stabilize the aircraft on a safe climb path and then proceed with the ENG FIRE
procedure.

IV.2 Engine Tailpipe Fire

Contrary to the engine fire, the engine tailpipe fire is harder to identify, and is
sometimes confused with an engine fire. It is also referred to as an “internal fire”
(i.e. located in the gas path).
A tailpipe fire will only occur on ground, during engine start or engine shutdown.
It is due to an excess of fuel in the combustion chamber, the turbine or the exhaust
nozzle, that ignites. It can result in a highly visible flame coming from the exhaust, or
in some smoke coming out of the engine (exhaust or inlet).

Figure 4
Engine Tailpipe Fire

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Whereas the tailpipe fire can be very spectacular, it usually has very little impact on
the engine. Indeed, it occurs in a part of the engine that is designed for very high
temperatures (1000 to 1200°C). However, it can have an impact on the aircraft itself
(e.g. damage to the flaps).
In the event of a tailpipe fire, there is no cockpit alert. The only indication may be
a rising EGT, due to the fire in the turbine. Therefore, tailpipe fires are more often
visually detected by cabin crew, ground crew or ATC. However, because cabin crew,
ground crew, or ATC usually do not know the difference between an engine fire and
a tailpipe fire, they usually report an engine fire to the flight crew. As a consequence,
the flight crew often applies the engine fire procedure, instead of the engine tailpipe fire
procedure.

The engine tailpipe fire procedure requests to:

• Shut down the engine in order to stop the fuel flow
• Dry crank the engine to remove the remaining fuel.

Do not use the ENG FIRE pushbutton (except for A300/310) or the AGENT DISCH
pushbuttons because:
• Pushing the ENG FIRE pushbutton will cut the FADEC power supply. This prevents
the dry crank sequence, which is the only effective action against a tailpipe fire
• The fire agents will be discharged outside of the engine core, in a part of the engine
that is not affected by the tailpipe fire (Figure 5). Discharging the fire agents will
have no negative impact on the engine, but may lead to delays or cancellation, if no
fire extinguisher bottle spare is available.

Extinguisher Agent
Distribution Zones

Tailpipe Fire Zones

Figure 5
Tailpipe Fire Zones

The engine tailpipe fire procedure should be sufficient to stop the fire. The intervention
of the fire brigade should therefore be a last resort (or if no bleed is available to dry

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crank the engine), because the ground fire extinguishing agent can cause serious
corrosive damage. Following the use of ground fire extinguishers, maintenance action is
due (the engine might be removed for a maintenance inspection).
In-service events show that engine tailpipe fire may lead to a precautionary, but
unwarranted, emergency evacuation.

IV.3 Engine Stall

An engine stall (also called engine surge) is in fact a compressor surge that can be
caused by:
• An engine deterioration (e.g. compressor blade rupture, or high wear)
• Ingestions of foreign objects (e.g. bird ingestion) or ice
• A bleed system malfunction
• A malfunction of the engine controls: Fuel scheduling or surge protection devices.

In a jet engine, air compression is achieved aerodynamically, as the air passes through
the stages of the compressor. If the air flowing over a compressor blade stalls,
the airflow is disrupted, and the compressor can no longer compress the incoming air.
The high-pressure condition existing behind the stalled area may create a flow reversal
towards the compressor air inlet, thus resulting in an immediate and large thrust loss.

During takeoff and high power settings, the engine stall is characterized by:
• One or more loud bangs
• Instant loss of thrust, resulting in a yaw movement
• Engine parameter (EPR/N1, N2 (or N3)) fluctuations and EGT increase
• Visible flames from the inlet and/or from the tailpipe.

(Source: FAA video Turbofan Engine Malfunction Recognition and Response)

Figure 6
Engine Stall at Takeoff

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Flight crews who have experienced an engine stall at takeoff report that the bang is
louder than any other noise they had previously heard in the cockpit. It is often
compared to a shotgun being fired a few meters away.
Because of the noise and yaw movement of an engine stall, flight crews sometimes
incorrectly identify the occurrence as a tire burst, or as a bomb. In-service events show
that a misinterpretation of an engine stall may result in rejecting the takeoff above V1,
causing a runway overrun.

At low power (e.g. at thrust reduction at top of descent), the engine stall is
characterized by:
• One or more muffled bangs
• Engine vibrations
• Engine parameter fluctuations and EGT increased.

An engine stall can result in an EGT overlimit condition because the airflow downstream
of the combustion chamber is not sufficient to ensure the cooling of the turbine.
Engine stalls are harder to detect at low power.

The engine stall can be:

• Recoverable without crew action
• Recoverable with crew action (or FADEC action)
• Not recoverable.

Recoverable stall without crew action

One or more loud bangs can be heard; the parameters fluctuate but quickly return to
normal. In most occurrences, the parameters are back to normal when the flight crew
checks the engine parameters. Consequently, it is hard to determine which engine has
stalled.
Engine operation can be checked by smoothly moving the thrust levers, one at a time,
to check the related engine response and stall-free operation.
Note that most recent engines include a stall detection system.
Flight crews should report the occurrence for immediate maintenance action.

Recoverable stall with crew action (or FADEC action)

Parameter fluctuations and bangs continue as long as the flight crew (or the FADEC)
does not retard the thrust lever, as per the ENG STALL procedure of the QRH or
the ECAM.
If the stall disappears at thrust reduction and the engine parameters are normal, the
flight crew can advance the thrust levers slowly, as long as the stall does not reoccur.

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If the stall reappears, keep the engine thrust below the stall threshold.
Flight crews should report the occurrence for immediate maintenance action.

Non recoverable stall

One or two bangs are heard and the engine will decelerate to zero power, as if the fuel
had been cut-off.
Bring the affected engine thrust levers to idle and shutdown the engine.
A non-recoverable stall can be accompanied by severe engine damage, if it is not
identified and corrected by the flight crew, and may lead to an engine failure.

IV.4 Engine Flameout

The combustion process has stopped. This can be due to many reasons such as:
• Fuel starvation
• Volcanic ash encounter
• Heavy rain/hail/icing
• Engine stall
• Control system malfunction

Flying at high speed and low engine thrust through heavy rain or hail increases the risk
of flameout.
The engine flameout will trigger a caution on the ECAM (if applicable).

When no caution is available, an engine flameout is detected by:

• A rapid decrease in EGT, N2 (N3 on RR engines), Fuel Flow, and N1
• The loss of the associated electrical generator.

On most FADEC equipped engines, continuous ignition will be automatically selected

when a flameout is detected. This ensures an automatic relight, if conditions permit.

IV.5 Engine Vibrations

Engine vibrations may be caused by:

• Engine unbalance
• Birdstrike or FOD causing blade deformation (Figure 7)
• Compressor blade loss
• Icing conditions (ice may build up on the fan spinner and blades).

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Figure 7
Fan Damage After a Birdstrike

In case the vibration level exceeds a certain level, the ECAM advisory function
(if applicable) will automatically highlight the affected engine.
When such a level of vibration is reached, there is potentially a loss of some mechanical
integrity of the engine (blade rupture, imbalance, …).

As a general rule, it is recommended to:

• Crosscheck the affected engine parameters (N1, N2, EGT, Oil press…) with the other
engine(s)
• Reduce the thrust level of the affected engine below the advisory level if flight
conditions permit.

A high N1 vibration level may be accompanied by perceivable airframe vibration.

A sudden increase of the vibration level indicates a possible deterioration of the engine.
During takeoff, the vibration indication should be stabilized once takeoff thrust is set.
If the advisory threshold is reached, a low speed rejected takeoff may be considered.
The vibrations should not vary significantly during the takeoff roll. If it suddenly
increases significantly, a rejected takeoff may be considered depending on
the circumstances.
Vibrations alone should not lead to an in-flight shutdown.

IV.6 Engine Parameter Overlimits (N1, N2, N3, EGT)

EGT Exceedance
The EGT redline is the only redline that can be exceeded occasionally without any
malfunction of the engine.
Due to the thermal inertia of the engine, the EGT reaches a peak at the end of
the takeoff roll, close to rotation or just after lift-off. The difference between

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the maximum permissible EGT (red-line) and the peak EGT during takeoff (with TOGA
thrust) is called the EGT margin. This EGT margin should be monitored by a dedicated
engine monitoring program.
As the engine ages, due to normal engine wear, the EGT margin will get smaller
(Figure 8). Indeed, due to a loss of efficiency, the engine will burn more fuel, which
will lead to a higher EGT. Consequently, the EGT margin is used as a parameter to
monitor the engine’s health.

EGT EGT Margin

EGT Redline Total

engine
hours

OAT

Figure 8
Evolution of the EGT with OAT and Engine Wear

The outside conditions also have an impact on the EGT.

This means that, exceptionally, the engine may exceed the EGT redline without any
failure. In this case, the engine continues to deliver its thrust. Consequently, if
the flight crew notices an EGT exceedance during the takeoff roll, the flight crew
continues the takeoff and establishes the aircraft on the initial climb path, before
applying the procedure.

Note:
A limited number of small EGT exceedances may be allowed (as per the Aircraft
Maintenance Manual), but must be reported in the logbook.

However, if the EGT suddenly increases when setting takeoff thrust, it is most likely
the symptom of a severe engine failure.

N1, N2, N3 Exceedance

N1, N2, N3 exceedances correspond to a malfunction of the engine.

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The associated procedure is usually to reduce thrust to return below the limits, and to
shutdown the engine if it is not possible to return below the limits, or depending on
the level of exceedance.

IV.7 Oil Low Pressure / Oil Low Level

In service experience shows that some rejected takeoffs and in-flight shutdowns have
been commanded because of a low oil level. However, a low oil level alone is not
a symptom of an engine malfunction.
On the other hand, a low oil pressure is the sign of an imminent engine failure.
Therefore, the published procedure must be applied.

IV.8 Reverser Unlocked

The full deployment of a thrust reverser in flight is a potentially catastrophic situation,
which can lead to the loss of control of the aircraft.

Therefore, the system is designed with adequate redundancy to ensure that

the reversers will deploy on ground only. There are three lines of defense (the details
may vary with aircraft and engine type) which:
• Lock the thrust reverser in the stowed position (with primary and secondary locks)
• Isolate the thrust reverser deployment system.

However, should a reverser be out of its fully stowed position, a REV UNLOCKED alert
will trigger:
• The first action is to reduce the thrust of the affected engine to idle (even if already
automatically reduced), and the aircraft speed (if applicable). This minimizes
the effect of a potential deployment. The affected engine must remain at idle for
the rest of the flight (i.e. even in the absence of buffet)
• The detection of buffet is the sign that the thrust reverser is at least partially
deployed. If detected, the flight crew should reduce the aircraft speed, and shut
down the affected engine.

V Operational Recommendations

This section provides flight crews with an overall awareness and understanding of
the main strategies to adopt in the case of an engine malfunction:
• Stabilize the aircraft trajectory
• Positively identify the affected engine, and the malfunction
• Apply the published procedure.

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It also provides guidelines on the prevention of unnecessary in-flight shutdowns, while

confirming the flight crew’s authority to take a precautionary decision/action,
depending on prevailing conditions.

Fly the Aircraft, not the Engine

Fly, Navigate, Communicate and Manage – in that order, as fostered by the Airbus
Operational Golden Rules.
This also applies in case of any engine malfunction. The priority is to stabilize
the aircraft trajectory before taking any action on the engine. Even in case of an engine
fire, stabilizing the aircraft trajectory before applying the associated procedure may
lead to further engine damage but will not affect safety.
The engines are certified in extreme conditions, in order to provide enough reaction
time to the crew to stabilize the aircraft, in case of a major engine malfunction, prior to
performing the associated procedure.
For example, the engine’s resistance to bird ingestion is tested. In accordance with
the FAR 33’s requirements, an engine at takeoff thrust must be able to withstand
the strike of a 3.65 kg bird, without catching fire, without releasing hazardous
fragments through the engine casing or without losing the ability to be shut down. It
must also be able to withstand the simultaneous ingestion of several (up to 4) smaller
birds (around 1kg), without losing more than 25% of thrust.
Similarly, during certification, the engine must be run during 5 minutes, with N1 and N2
(N3 if applicable) at the red line, and EGT 42°C above the red line. Following this run,
the engine must be serviceable.

(Source: FAA video Turbofan Engine Malfunction Recognition and Response)

Figure 9
Engine Certification Tests

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No RTO above V1
In line experience shows that engine malfunctions during takeoff occasionally lead to
rejected takeoffs above V1, which have caused runway excursions, ranging from
incidents to fatal accidents/hull losses.
The most frequent cause of rejected takeoff above V1 is the engine stall. The flight
crew is usually startled by the loud bang and the yaw movement, and consequently
believes the aircraft is not airworthy. In all the reported cases, the aircraft actually was
fit to fly.
Similarly, engine fire warnings have also led to rejected takeoffs above V1.
From a system point of view, the engine is certified to ensure that it can sustain
an engine fire for a few minutes without affecting the safety of the aircraft. From
a performance point of view, engine failure at or after V1 is taken into account in
the takeoff performance computation. However, in many engine failure cases,
the engine is still able to deliver some thrust during a significant period of time.

If not sure which Engine is malfunctioning, keep-it running

Several accidents or incidents have been caused by a rushed decision to shutdown
an engine, due to the inability to correctly assess which engine was malfunctioning.
If the analysis of the instruments is not enough, the crew should smoothly move
the thrust levers and check the proper variation of the engine parameters.

If possible, keep the Engine running

In-service experience shows that, when the flight crew notices a drift of the engine
parameters (EGT, vibrations, advisory level, etc…), they often decide to perform
a preventive engine shutdown.
However, unless a procedure requires an engine shutdown, it is usually preferable
to keep the engine running.

Even at idle, the engine:

• Provides electric, hydraulic and bleed power redundancy
• Produces less drag than a windmilling engine.

An ECAM advisory (if applicable) is an indication that a parameter is still in its normal
range but is drifting away. It is meant for crew awareness (attention getter) and
monitoring. The guidelines associated to the advisory conditions are provided in
the FCOM/QRH. Consequently, except for engine vibrations, no action should be taken
based only on the advisory.

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If possible, restart the Engine

If the engine has failed or flamed out, and there is no indication of engine damage, it is
always possible to attempt to restart the engine.

Engine damage can be suspected if some of the following symptoms are observed:
• Rapid increase of EGT above the red line
• Important mismatch of rotor speeds (N1 vs. N2 or N3) or absence of rotation
• Abnormal oil pressure/temperature
• Loud noise
• Fumes or burning smell in the cabin.

If a visual check is possible, the crew should look for damage to the engine cowling or
aircraft structure, or missing engine parts.

VI Summary of Key Points

• During their career, most pilots will experience engine malfunctions, but most of
them will never encounter a severe engine malfunction leading to an in-flight
shutdown
• Reported in-service events show that incorrect crew response to an engine
malfunction has remained constant for many years
• Full flight simulators are very powerful training tools but are not fully representative
of engine malfunctions and their consequences.

Therefore, to safely and efficiently manage engine malfunctions, flight crews should:
• Stabilize the aircraft trajectory before dealing with the malfunction
• Never rush to shutdown the affected engine during critical flight phases: Engines
have been certified in extreme conditions
• Know how to identify various engine malfunctions and their consequences.

Any engine malfunction should be reported to the maintenance.

Airlines should consider the various references provided by the manufacturer’s

operational documentation and by the industry to address, at all stages of the training,
engine related indications and their relation to engine malfunctions.

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VII Associated Flight Operations Briefing Notes

The following Flight Operations Briefing Notes provide expanded information on:
• Operations Golden Rules
• Birdstrike Threat Awareness
• Volcanic Ash Awareness
• Revisiting the Stop or Go Decision

VIII Airbus References

• Flight Crew Operating Manuals (FCOM) – Abnormal and Emergency Procedures –
Power Plant
• A300-600/A310 FCOM Bulletins - Preventing Unnecessary In-Flight Shutdowns
• A330/A340 FCOM Bulletins - Preventing Unnecessary In-flight Shutdowns
• A320 Family & A330/A340 Family & A380 Flight Crew Training Manuals (FCTM) –
Abnormal Operations

IX Additional Reading Materials / Website References

• Flight Safety Digest November-December 1999 - Propulsion System Malfunction
Plus Inappropriate Crew Response (PSM+ICR)
• Flight Safety Digest March 2001: Understanding Airplane Turbofan Engine Operation
Helps Flight Crews Respond to Malfunctions
Note: These documents can be found on the Flight Safety Foundation website:
http://www.flightsafety.org/ao_home.html.
• FAA Training Material (Video) – Engine Malfunctions, Recognition and Response

This FOBN is part of a set of Flight Operations Briefing Notes that provide an overview of the applicable standards,
flying techniques and best practices, operational and human factors, suggested company prevention strategies and personal
lines-of-defense related to major threats and hazards to flight operations safety.

This FOBN is intended to enhance the reader's flight safety awareness but it shall not supersede the applicable regulations
and the Airbus or airline's operational documentation; should any deviation appear between this FOBN and the Airbus or
airline’s AFM / (M)MEL / FCOM / QRH / FCTM, the latter shall prevail at all times.

In the interest of aviation safety, this FOBN may be reproduced in whole or in part - in all media - or translated; any use of
this FOBN shall not modify its contents or alter an excerpt from its original context. Any commercial use is strictly excluded.
All uses shall credit Airbus.

Airbus shall have no liability or responsibility for the use of this FOBN, the correctness of the duplication, adaptation or
translation and for the updating and revision of any duplicated version.

Airbus Customer Services

Flight Operations Support and Services
1 Rond Point Maurice Bellonte - 31707 BLAGNAC CEDEX FRANCE
FOBN Reference : FLT_OPS – SUPP_TECH – SEQ 07 – REV 01 – DEC. 2006

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