Stall Avoidance Training

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AERODYNAMIC STALLS
In-Flight Loss Of Control (ILOC) as a result of an
aerodynamic stall has been one of the most
significant causes of fatal Army Fixed-Wing
aircraft accidents for many years. Loss of control
usually occurs because the aircraft enters a flight
regime which is outside its normal envelope,
usually, but not always at a high rate, thereby
introducing an element of surprise for the flight
crew involved.
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DAC Clark J Wilson

Purpose Of Stall Avoidance
Training
• Recognize the symptoms of an approaching stall
(such as slow airspeed, sloppy controls and or
maneuvering at more than 1G) and instinctively recover.
• Instill a habit formation so that a pilot’s reaction to an
approaching wing stall is always timely reduction in the
angle of attack.

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DAC Clark J Wilson

Stall Avoidance
A pilot should use all energy resources
available, including altitude and power as
appropriate to prevent or recover from an
approaching stall condition.

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DAC Clark J Wilson

Stall/Loss of Control Avoidance
Training
Aviators should be trained to instinctively recognize and
recover from:
• Approach to stalls
• Fully developed stalls
• Stall situations that are unexpected
Stall/Loss of Control Training should not emphasize initial
stall recovery with a minimum loss of altitude and/or a
target pitch attitude but an immediate reduction in the
angle of attack.
Stall/Loss of Control Training should not be associated
the with the “Go-Around” maneuver .
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DAC Clark J Wilson

The Aerodynamic Stall
STALL: AN ABRUPT, but not always abrupt, LOSS OF LIFT AND

INCREASE IN DRAG THAT OCCURS WHEN AN AIRFOIL EXCEEDS
ITS CRITICAL ANGLE OF ATTACK (AOA) WHICH IS ABOUT 18º to
22º AOA.

BASIC PRINCIPLES:
•
•
•
•
•

BOUNDARY LAYER
LAMINAR FLOW
TRANSITION REGION
TURBULENT LAYER
SEPARATION

ANGLE OF ATTACK (AOA)
RELATIVE WIND
CRITICAL AOA

WING TWIST:
•
•
•
•
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18º
ROOT TO TIP
RELATIV
E WIND
STALL BUILDS INSIDE OUT
( MCA)
MAINTAIN AILERON EFFECTIVENESS
DAC Clark J Wilson

Airplane Wing Stall
View:
Airplane Stalls, King Video

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DAC Clark J Wilson

Approach to Stall vs. Full Stall

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DAC Clark J Wilson

An airplane wing can be stalled at Any:
• Airspeed
• Altitude
• Attitude (Pitch Attitude in relation to the horizon has
no relationship to the aerodynamic stall)
Given an airplane with the same weight, configuration
and G loading, the Indicated Air Speed (IAS) at
which a stalls occurs remains constant regardless of
True Air Speed (effects of pressure altitude and
temperature)
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DAC Clark J Wilson

Wing stalls typically occur following :
• Speed reduction
• Premature flap retraction
• Increased wing loading (G)
Stalls can be aggravated by Ice contaminated
wing surfaces.

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DAC Clark J Wilson

Approach to Stall or Stall
Recovery
•
•
•
•

•
•

A Preventive actions must (ideally) be taken before the stall
warning.
An approach to a stall is a controlled flight condition.
A fully developed stall is an out-of-control, but usually recoverable
condition.
The recovery procedure for both the approach to a stall and the
fully developed stall should be an immediate reduction in angleof-attack.
Most full stall and approach to stall incidents have occurred
where there was sufficient altitude available for recovery.
Stall incidents that progress into accidents occurred because the
crew failed to make a positive recovery when the stall warning
occurred resulting in a condition that progressed to a full stall.

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DAC Clark J Wilson

Stall Recovery is the Priority.
Altitude recovery is secondary to Stall
Recovery
• The approach to stall recovery should not emphasize
“Powering Out” of the approach to stall condition without
also releasing back pressure on the elevator control. The
“Powering Out” technique may be impracticable at
altitude due to thrust available. At near stalled angle of
attack, drag is high and available thrust for acceleration
could be too slow to effect an optimum recovery.
• Do not increase back pressure unless ground contact is
imminent.
• If a go-around maneuver is to be performed, accelerate
until all stall warnings have ceased before pitching to a
climb attitude.
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DAC Clark J Wilson

Altitude Loss During Stall Recovery
There are many variables which could affect the amount of altitude loss encountered in a
smooth recovery from an approach to stall. These variables may include, but are not
limited to:
•
•
•
•
•

Entry Altitude
Bank Angle
Aircraft Weight
Aircraft Configuration
Density Altitude

The reduction of angle of attack required to initiate recovery will most likely result in
altitude loss. The amount of altitude loss will be affected by the operational environment.
Training programs and evaluation standards should not mandate a predetermined value for
altitude loss for stall recovery. Proper evaluation criteria should consider the multitude of
external and internal variables which affect the recovery altitude. The aircraft manufacturer’s
recommended stall recovery techniques and procedures take precedence and should be
followed.

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DAC Clark J Wilson

The only recovery procedure that is
valid for the approach to stall and full
stall is to release the back pressure
on the control column and
simultaneously apply power until a
safe airspeed is attained. If stall
warnings are still indicated, continue
pitching below the level pitch attitude
until all stall warnings cease.
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DAC Clark J Wilson

Stall Speed Is Increased
When Flaps Are Retracted
Retracting the flaps prematurely in the RC-12 will reduce lift
and increase the indicated stall speed:
•

Selecting flaps from Full Flaps (100%) to Approach Flaps (40%)
– Effects about a 10 Knots increase in stall speed

• Selecting flaps from Full Flaps (100%) to Approach Flaps
(40%) – Effects about a 10 Knots increase in stall speed
Any sudden retraction of flaps at slow speed or during an
approach to stall recovery may result in a possible fully
developed stall and loss of aircraft control.
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DAC Clark J Wilson

FULL STALLS
• The successful recovery from a fully
developed stall involves a very different
technique compared to the recovery from
the approach to stall.
• Recovery from a full stall without reducing
pitch attitude is impossible and will
certainly require a significant loss of
altitude.
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DAC Clark J Wilson

ACCELERATED STALLS
• The accelerated stall occurs when an aircraft
experiences a load factor (G) higher than 1G, for
example while turning or pulling up from a dive.
• An aircraft can theoretically be stalled at any speed.
An aircraft experiencing a load factor greater than
1G will stall at a higher indicated airspeed speed
compared to its wings level, un-accelerated stall
speed.
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DAC Clark J Wilson

Accelerated Stall In A Turn
The higher wing loading in a turn due to the higher centrifugal
force causes the aircraft to stall at higher speeds compared to the
straight and level stall speed.

View: Accelerated stall Video
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DAC Clark J Wilson

Deep Stalls
• Due to the T-Tail design, C-12 and RC-12 aircraft may not
manifest the buffeting, pitching and rolling characteristics that
typically indicate a stall condition in other fixed-wing aircraft.
• A deep wing stall develops when the angle of attack increases
well beyond the wing’s critical stall point, aggravated by the T-tail
configuration.
• Initially, the T-Tail aircraft’s elevator remains effective even
after the wing has stalled because the T-Tail remains above the
wing’s wake.
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DAC Clark J Wilson

T-TAIL Deep Stall

• The elevator remaining effective after the wing has stalled could cause the pilot to inadvertently pitch-up to an even greater Angle
of Attack (AOA) and into a deep stall.
• In a fully developed deep stall the horizontal tail surfaces becomes buried in the wing’s wake and the elevator may then lose all
effectiveness, making it impossible to reduce pitch attitude and break the stall.
• In the deep stall regime the enormous increase in drag at low speeds can cause an increasingly descending flight path with no
change in pitch attitude which further increases the AOA.
• Once the deep stall is fully developed there is no guarantee that recovery may be affected by down-elevator movement and it may
be impossible to affect a nose-down pitch attitude to increase airspeed.
.
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DAC Clark J Wilson

DEEP STALL RECOVERY
• The Deep stall is characterized by a level
pitch attitude, however, the actual flight
path may exceed 45 degrees down and a
sink rate of up to 8500 feet per minute.
• Deep Stall recovery requires a 10 – 15
degrees nose–down pitch change to brake
the stall. Allow airspeed to increase to at
least 25 KIAS above stall speed.
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DAC Clark J Wilson

Ice Contamination On Wings
• Any ice (including frost) adhering to the wing surfaces of an aircraft will

significantly increase drag and its stall speed. Ice forming aft of the de-ice
boot is especially dangerous.
• The Stall Warning System in the C-12 (Stall Horn) normally activates about
5-10 Knots above a stall, but with ice on the wings, the Stall Warning System
may not activate before a full stall develops.
• With an ice contaminated wing, an abrupt full stall may occur without the
typical pre-stall warning, i.e. buffet, pitch–down. A brisk reduction in pitch
attitude is required to recover.
• When landing with any ice adhering to the wings, “as a rule of thumb”,
VREF should be increase by 10 Knots IAS.

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DAC Clark J Wilson

APPROACH TO STALL
RECOVERY
At the first sign an approaching wing stall (Stall Warning Horn, pre-stall
airframe buffet, loss of control effectiveness and/or nose
pitch-down):
1. Decrease angle of attack by simultaneously:
• Reducing Pitch Attitude to a measured amount depending upon
proximity to the ground and
• Simultaneously Adding Power
2. Maintain coordinated flight.
3. Roll wings level. An airplane in a turn has higher wing loading which
increases the stall speed.
4. Increase airspeed well above the stall warning airspeed before
retracting flaps.
5. After the recovery is complete, proceed with a Go-Around if required,
Missed Approach, Stabilized Approach and Landing or appropriate
with the flight regime.
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DAC Clark J Wilson

DURING APPROACH TO
STALL RECOVERY
• Be prepared to manage control forces for required pitch
inputs.
• An actual stall usually but not always results in a nosedown pitch. Too much forward movement of the control
column can produce an excessive nose-down attitude.
• As power and airspeed are increased, a pitch-up
tendency may be induced.
• The GO-Around button may be pressed to set a maximum
pitch limit during recovery.
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DAC Clark J Wilson

CREW COODINATION
PILOT FLYING (P*):
1. Communicate positively at the first indication of a wing stall warning, call:
“Stall Warning”
2. Disconnect AUTOPILOT/YAW DAMPER.
3. Decrease angle of attack immediately by:
• Releasing back pressure. (DO NOT HOLD OR INCREASE PITCH
ATTITUDE UNLESS GROUND CONTACT IS IMMINENT! ) and
• Advancing the POWER LEVERS to the maximum allowable power
position and call:
“Set Power”
5. Roll wings level.
6. Maintain coordinated flight.
7. Do not initially change gear or flap configuration.

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DAC Clark J Wilson

MAINTAIN COORDINATED
FLIGHT
• One wing may drop if the aircraft is in an un-coordinated yaw
at the onset of a stall. Adverse yaw could result in a spin
unless coordinated flight is maintained by proper rudder
control.
• When power is applied, a yaw may be induced by one
engine spooling-up faster than the other.
• Even though excessive aileron pressure may have been
applied, a spin should not occur if directional (yaw) control is
maintained by a timely application of coordinated rudder
pressure.

STEP ON THE BALL
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DAC Clark J Wilson

CREW COODINATION
PILOT FLYING (P*) (Continued):
8. If a Go-Around is to be performed because of a resulting unstable
approach situation, retract flaps only when a safe airspeed margin
above stall is established:
• Call for flaps to be selected from the full down position to the
approach position only after accelerating to a safe airspeed (about
10 knots above stall warning speed) and the descent has been
stopped.
• Retract the landing gear as required when a positive rate of climb
call is heard or indicated.
• Call for flaps to be selected from the approach position the full-up
position at or above Vyse.
• Call for “GO-AROUND” Checklist and accomplish a
go- around/missed approach if applicable.
9. Otherwise, reestablish appropriate flight regime and configuration.
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DAC Clark J Wilson

CREW COORDINATION
PILOT NOT FLYING (P):
1. Communicate positively - At the first indication of wing stall
warning, call:
“Stall Warning”.
2. Offer assistance - Guard the controls and be prepared to assist P*
with pitch and power if required.
3. Provide aircraft control advisories - Monitor pitch attitude. If pitch is
increasing above 7° nose-up pitch attitude call:
“Pitch Down”.
4. Directed assistance - Assist P* in increasing POWER LEVERS to
the maximum controllable power position and setting PROPELLER
LEVERS to MAX RPM position.
5. Cross-monitor performance by verifying that the airspeed increases.
6. Provide obstacle advisories - Monitor proximity to terrain.
7. Monitor airspeed. If airspeed is decaying close to the stall warning
speed:
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“Increase Airspeed”.

WARNING
• The autopilot should be disconnected when operating in
severe icing conditions. The autopilot may mask tactile cues
that indicate adverse changes in handling characteristics.
• The stall warning horn may be unreliable in icing conditions
as an actual aerodynamic wing stall may occur well before the
stall warning horn activates.
• The stall warning horn normally activates 5 to 10 Knots
above the actual stall. A wing contaminated with ice may stall
at least 10 knots above the stall speed of a clean wing.
•
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DAC Clark J Wilson

FULL STALL RECOVERY
TRAINING
• Recoveries from Full Stall conditions may be performed
only in a compatible simulator and is required to be
demonstrated only during initial aircraft qualification at
USAAVNC, Ft. Rucker, AL.
• As a part of all stall avoidance training, IPs should
discuss the indications and recovery procedures for
Full Wing Stalls, Ice Contaminated Tail-Plane Stalls
and Accelerated stalls.
• Chapters 8 in the Operator’s Manual addresses full stall
and spin recovery techniques.
11/17/13

DAC Clark J Wilson

RC-12 FULL STALL
RECOVERY
• If a full wing stall occurs, briskly move
the control column forward to a
nose-down attitude.
• Level the airplane after airspeed has
increased approximately 25 knots
above the stall.
AVOID A SECONDARY STALL DURING
THE PULL-UP
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DAC Clark J Wilson

WING DROP
• If one wing drops in a stalled condition,
apply up wing rudder to level the
wings.
• Using ailerons to level wings in a
stalled condition may aggravate the
stall recovery.

11/17/13

DAC Clark J Wilson

RC-12 SPIN RECOVERY
• Power levers – IDLE
• Apply full rudder opposite the direction of spin rotation.
• Simultaneously with rudder application, push the control
wheel forward and neutralize ailerons.
• When rotation stops, neutralize rudder.
CAUTION – Do not pull out of the resulting dive too
abruptly as this could cause excessive wing loads and
possible secondary stall.
• Pullout of dive by exerting a smooth, steady back
pressure on the control wheel, avoiding an accelerated
stall and excessive aircraft stress.
11/17/13

DAC Clark J Wilson

Ice Contaminated Tailplane Stall
(ICTS)
Since the horizontal stabilizer acts to counter the natural nose-down
tendency caused by the wing lift moment, the airplane reacts by
pitching down—often abruptly—when the tailplane is stalled.
There is no evidence that the RC12 is uniquely susceptible to ICTS.
Compared to other airplane designs, C-12 airplanes may be less
susceptible to ICTS for the following reasons:
• In the T-tail configuration, the horizontal stabilizer is above the wing
downwash induced higher AOA on the horizontal stabilizer.
• The C-12 has a pneumatic deicing system that is effective in
removing ice accumulation.
That is not to say that the C-12 is immune to ICTS.
View the NASA Tailplane Icing Stall Video . This illustrates the
differences between the Wing Stall and the ICTS.
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DAC Clark J Wilson

Effects of Flaps on Inducing
ICTS
ICTS typically occurs when flaps are extended to
the landing position because:
• Flap extension increases the wing airflow
downwash angle on the horizontal tailplane thus
increasing its negative angle of attack (AOA).
• Flap extension also reduces the aircraft angleof-attack (AOA) and increases nose-down
pitching moment which requires more tail
download, all of which in turn result in an
increased negative AOA at the horizontal
tailplane.
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DAC Clark J Wilson

Flaps and Tailplane AOA

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DAC Clark J Wilson

Ice Induced Tailplane Stalls
Usually Occur When:
•
•
•
•

Wing flaps are extended;
Engine power is increased;
The pilot makes a nose-down control input;
The airplane increases speed or encounters gust
conditions; or
• A combination of these factors with flaps extended.
Note: Full flap extension is generally the only case that
results in ICTS but this may not be true for all designs,
particularly those with closely spaced flap settings.
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DAC Clark J Wilson

ICTS Recognition
Pilots may sense ICTS or impending ICTS as
one or a combination of:
• Difficulty to trim in the pitch axis.
• Pulsing or buffeting of the longitudinal
control; or
• Lightening of longitudinal control push force
or an increase in pull force necessary to
command a new pitch attitude.
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DAC Clark J Wilson

WING STALLS AND ICE CONTAMINATED TAILPLANE STALLS (ICTS)
HAVE DIFFERENT RECOGNITION CHARACTERISTICS AND REQUIRE
DIFFERENT RECOVERY ACTIONS

Stall Warning Horn

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DAC Clark J Wilson

A PILOT’S INCORRECT REACTION TO
STALL WARNING
The National Transportation Safety Board
(NTSB) determined the probable cause of the
Feb. 12, 2009, Colgan Air Flight 3407 crash was
the captain’s inappropriate response to an
activation of the stick shaker — a clear warning
of an imminent stall.
NTSB Simulated Video of Colgan Air Flight
Accident

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DAC Clark J Wilson

Wing Stall vs. ICTS
The Colgan Air Flight 3407 accident was the result of the pilot’s inappropriate
response to an activation of the stick shaker Stall Warning System.

WHY?
• Colgan Air pilot training emphasized that a pilot’s reaction to a stall warning
event must result in a minimum loss of altitude, achieved by holding
positive back pressure on the elevator and “powering out of the stall”.
Or…
• The pilots may have incorrectly interpreted the activation of the Stall
Warning System as an ICTS condition for which the pilot responded with
increased back pressure on the elevator and a premature flap retraction
which resulted in a fully stalled wing.
The bottom line is if the Colgan Air pilot had relieved back pressure rather
than pulled on the elevator control, 50 people may still be alive today
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DAC Clark J Wilson

Air France Flight 447
•

Air France Flight 447 was a scheduled airline flight involving an Airbus
A330-200 aircraft that crashed into the Atlantic Ocean on 1 June 2009,
killing all 216 passengers and 12 aircrew.

•

The latest reports from accident investigators state that the aircraft crashed
following an aerodynamic stall.

•

The pilot repeatedly pulled back on the stick, producing a stall, continuing
even while the stall warning sounded continuously for 54 seconds.

•

http://www.youtube.com/watch?v=HSTiax4pvZ4&feature=related

•

http://www.youtube.com/watch?v=ARybu2kHeZ8&feature=related

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DAC Clark J Wilson

In-flight Loss of Control Avoidance and
Upset Recovery Training
The Airline Pilots Association (ALPA)’s Human Factors and Training
Group and Training Council:
• Has identified In-Flight Loss of Control (ILOC) as one of the leading
causes of aircraft accidents worldwide and
• Has recommended enhanced academic requirements for initial and
recurrent pilot training on the aerodynamics of normal flight,
approach to stall, impending stall, full stall and abnormal flight
conditions, including the appropriate use of primary and secondary
flight controls.
http://www.apstraining.com/2010/alpa-speaks-on-upset-recoverytraining/

11/17/13

DAC Clark J Wilson

• As a result of the Air France Flight 447 crash, other recent crashes
and the NTSB findings concerning the Colgan air disaster, the FAA has
issued an Information For Operators (InFO) and a Safety Alert For
Operators (SAFO #10012, DATED: 7/6/10).
•The FAA is revising the FAA Practical Test Standards (PTS) for the
approach to stall recovery in transport category airplanes. The old
standard for the approach to stall recovery that emphasizes pitching to
nose-up attitude in order to recover with a minimal loss of altitude is no
longer valid.
• The industry is now changing the approach to stall recovery to
emphasize reducing the angle of attack with the elevator control at the
first indication of an impending stall, then increasing power.
• Using power levers as the primary control in recovering from the
approach to stall is no longer a valid technique.
11/17/13

DAC Clark J Wilson

QUESTIONS?
FLY SAFE!

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DAC Clark J Wilson

Stall Avoidance Training

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