Wake turbulence
UPL Safety Seminar 2012
Contents
Definition
Factors which affect wake turbulence
Wake categories
Statistics
Hazard
Avoidance
Wake turbulence definition
Results from the forces that lift the
aircraft
NO LIFT = NO WAKE TURBULENCE !!!
Wake turbulence definition
Wake turbulence consists of a pair of
vortices trailing from the wing tips of
an aeroplane. They are caused by
the differential pressure between the
top and the bottom surfaces of the
lift-producing wing
Wake turbulence definition
Vortices have a counter rotating
flow, the direction of which is from
under the wing where the pressure
is high, around the wing tip to the
top of the wing where the pressure
is low
Wake turbulence definition
The wake turbulence associated with
helicopters also results from high
pressure air on the lower surface of
the rotor blades flowing around the
tips to the lower pressure region
above the rotor blades.
Mouvement of the wake turbulence:
en route
Mouvement of the wake turbulence:
approach and take off
Factors which affect the wake
turbulence
Weight
Speed
Configuration
Wingspan
Angle of attack
Factors which affect the wake
turbulence
Atmospheric stability
Wind strength and direction
Ground effect
ICAO wake turbulence category
L (Light) aircraft types of 7 000 kg
(15 500 lbs) or less.
ICAO wake turbulence category
M (Medium) aircraft types less than
136 000 kg (300 000 lbs) and more
than 7 000 kg (15 500 lbs).
ICAO wake turbulence category
H (Heavy) aircraft types of 136 000
kg (300 000 lbs) or more.
ICAO wake turbulence category
Super Heavy for Airbus A380-800
with a maximum take-off mass in
the order of 560 000 kg.
National variations
Statistics
Statistics
Statistics
Most accidents occur during
approach at very low heights (less
than 200 feet above the runway
threshold)
90 percent of wake turbulence
accidents involve aircraft that weigh
less than 13 600 kg (30 000 lb)
In 99 percent of the reported
events, the effects of wake
turbulence are abrupt and occur
without any advance warning
The Hazard
The induced rolling moment can
exceed the roll control
The Hazard
The capability of an aircraft to
counteract the roll imposed by the
vortex primarily depends on the
wingspan and the control
responsiveness of the encountering
aircraft
Counter control is more difficult for
encountering aircraft with wingspans
that are relatively shorter than that
of the generating aircraft.
The Hazard
“brick wall” encounters where the
aircraft experiences a rather abrupt
displacement.
occur en route when the
encountering aircraft crosses
through the wake of the generating
aircraft.
The Hazard
Counter control is most effective and
induced roll minimal where the
wingspan of the encountering
aircraft is outside the rotational flow
field of the vortex.
Recovery from induced roll
RECOMMENDED VISUAL
AVOIDANCE PROCEDURES
Landing Behind a Larger Aircraft -
Same Runway
Stay at or above the larger aircraft’s
final approach flightpath.
Note its touchdown point.
Land beyond the touchdown point,
runway length permitting.
If unable to land safely beyond the
touchdown point, go around.
Landing Behind a Larger Aircraft -
Same Runway
Landing Behind a Larger Aircraft -
Parallel Runway Closer Than 2500ft
Consider possible wake-turbulence
drift to your runway.
Stay at or above the larger aircraft’s
final approach flightpath.
Note its touchdown point.
Land beyond the touchdown point,
runway length permitting.
If unable to land safely beyond the
touchdown point, go around.
Landing Behind a Larger Aircraft -
Parallel Runway Closer Than 2500ft
Landing Behind a Larger Aircraft -
Crossing Runway
Cross above the larger aircraft’s
flightpath.
Consider lateral and vertical motion
of wake turbulence.
If unable to land safely, go around.
Landing Behind a Larger Aircraft -
Crossing Runway
Landing Behind a Departing
Larger Aircraft - Same Runway
Note the larger aircraft’s rotation
point.
Land before the rotation point, or go
around.
Landing Behind a Departing
Larger Aircraft - Same Runway
Landing Behind a Departing
Larger Aircraft - Crossing Runway
Note the larger aircraft’s rotation
point. If past the intersection,
continue the approach and land
before the intersection.
If larger aircraft rotates before the
intersection, avoid flight below
larger aircraft’s flightpath. Abandon
the approach unless a landing is
assured well before reaching the
intersection.
Landing Behind a Departing
Larger Aircraft - Crossing Runway
Departing Behind a Larger Aircraft
Note the larger aircraft’s rotation
point.
Delay, do not begin take-off roll
unless your rotation point will be
prior to the larger aircraft’s rotation
point.
Continue climb above the larger
aircraft’s climb path until turning
clear of its wake. Caution: This may
not be possible because of the larger
aircraft’s performance.
Departing Behind a Larger Aircraft
Departing opposite direction of a
Larger Aircraft
Intersection Takeoffs - Same
Runway
Be alert to adjacent larger aircraft
operations, particularly upwind of
your runway.
If intersection take-off clearance is
received, avoid headings which will
cross below a larger aircraft’s path.
Ensure your rotation point is before
larger aircraft’s rotation point, or
delay takeoff.
Intersection Takeoffs - Same
Runway
En Route Within 1000 Feet
Altitude of a Large Aircraft's
Altitude
Avoid flight below and behind a large
aircraft’s path.
If a larger aircraft is observed above
and on the same track (meeting or
overtaking), adjust your position
laterally, preferably upwind.
En Route Within 1000 Feet
Altitude of a Large Aircraft's
Altitude
RECOMMENDED IFR
AVOIDANCE PROCEDURES
ICAO Prescribed Separation Minima
The ICAO minima are detailed and
illustrated in PANS-ATM Doc 4444
They are defined for aircraft under
ATC control which have not reported
the preceding aircraft in sight and
have been instructed to follow and
maintain their own separation from
that aircraft visually
ICAO Prescribed Separation Minima
If the latter occurs in the case of an
IFR aircraft then the pilot-in-
command of the aircraft concerned
becomes responsible for ensuring
that the spacing from a preceding
aircraft of a heavier wake turbulence
category is acceptable.
ICAO Prescribed Separation Minima
The distance between two aircraft on
arrival or departure is used where
radar separation of traffic is being
applied and the time between the
successive passage of two aircraft at
a point is used where procedural
separation applies.
Minimum distance separation
Minimum distances apply whenever:
an aircraft directly follows another at
the same altitude or less than 1,000
ft below it, or
if both aircraft are using the same
runway or parallel runways
separated by less than 760 m or
an aircraft is crossing behind
another aircraft, at the same altitude
or less than 300 m (1 000 ft) below.
Using ILS Glideslopes for Vertical
Separation
When ILS approaches are being
used, consideration may be made by
the pilot of the trailing aircraft to fly
at or above the ILS glideslope
Using ILS Localizer for Lateral
Separation
During crosswind conditions, pilots
may consider flying offset on the
upwind side of the localizer
centerline as a means of avoiding
the leader’s wake turbulence.
Wake Turbulence Separation Minima
- Departures
Conclusions
Avoid being below and behind
heavier aircraft
Respect the separations
Take ATC warnings serious
Be prepared for recovery
Have safe flights
Questions ?
???
References
FAA Wake Turbulence Training
Aid
UK NATS AIC: P 064/2009
ICAO Aircraft type designators
http://legacy.icao.int/anb/ais/8643/ind
ex.cfm
www.skybrary.aero
