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 06/12/22 DAC Clark J Wilson

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Stall avoidance training and pilot evaluations of approach to stall recovery procedures must develop essential habit formations that instill recognition and proper recovery from imminent and full stall situations. Using power as the primary control without a reduction in elevator backpressure while recovering from an approach to stall does not instill habit formation for effective stall avoidance and aircraft upset recovery.

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Page 1: Stall Avoidance Training

.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. 04/11/23 DAC Clark J Wilson

Page 2: Stall Avoidance Training

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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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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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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The Aerodynamic StallSTALL: 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

WING TWIST:• ROOT TO TIP• STALL BUILDS INSIDE OUT• ( MCA)• MAINTAIN AILERON EFFECTIVENESS

RELATIVE WIND

ANGLE OF ATTACK (AOA)

RELATIVE WIND

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18º

CRITICAL AOA

Page 6: Stall Avoidance Training

Airplane Wing Stall

View:

Airplane Stalls, King Video

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Approach to Stall vs. Full Stall

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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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Wing stalls typically occur following :

• Speed reduction• Premature flap retraction• Increased wing loading (G)

Stalls can be aggravated by Ice contaminated wing surfaces.

Page 10: Stall Avoidance Training

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 angle-of-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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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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Altitude Loss During Stall Recovery

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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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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.

Page 14: Stall Avoidance Training

Stall Speed Is Increased When Flaps Are Retracted

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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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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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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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Accelerated Stall In A Turn

View: Accelerated stall Video

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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.

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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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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.. 04/11/23 DAC Clark J Wilson

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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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Page 21: Stall Avoidance Training

Ice Contamination On Wings

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• 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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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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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 nose-down 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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Page 24: Stall Avoidance Training

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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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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Page 26: Stall Avoidance Training

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.

 

CREW COODINATION PILOT FLYING (P*) (Continued):

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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:

“Increase Airspeed”.

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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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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.

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Page 30: Stall Avoidance Training

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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Page 31: Stall Avoidance Training

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.

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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.

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Page 33: Stall Avoidance Training

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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Page 34: Stall Avoidance Training

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 angle-of-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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Flaps and Tailplane AOA

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

DIFFERENT RECOVERY ACTIONS

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Stall Warning Horn

Page 39: Stall Avoidance Training

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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Wing Stall vs. ICTSThe 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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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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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-recovery-training/

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• 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.

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QUESTIONS?

FLY SAFE!

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