Update on stall procedure
May 201117th Performance and Operations Conference
Presented byXavier LESCEU – Test Pilot & Operational Expert Pilot
17th Performance and Operations Conference in Dubai
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Contents
May 201117th Performance and Operations Conference
Stall phenomenon1
AoA control2
Stall recovery3
New procedure4
Conclusion5
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Aerodynamic Review
Page 3
For a given configuration, a given speed and a given altitude,
Lift is only linked to AoA
For a given aircraft configuration and speed
An aircraft stalls for a given AoA
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Stall
• A loss of speed can result in an aircraft reaching the stall AoA
• BUT it remains an AoA issue
Stall is only an AoA problemLow speed is a common contributing factor
Page 4
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Contents
May 201117th Performance and Operations Conference
Stall phenomenon1
AoA control2
Stall recovery3
New procedure4
Conclusion5
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
AoA Control – Pitch control effect
The pitch control is a direct AoA commandThe elevators control DIRECTLY the AoA.
A nose down command has an IMMEDIATE effect :
AoA
CG
Page 6
Nose down command ⇒ AoA decrease
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
AoA Control – Thrust effect
• Aircraft with engines below the aircraft Center of Gravity⇒Thrust has a significant pitch effect
Thrust increase ⇒ AoA increase
CG
Thrust increase
AoA
Page 7
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Contents
May 201117th Performance and Operations Conference
Stall phenomenon1
AoA control2
Stall recovery3
New procedure4
Conclusion5
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Stall Recovery When Aircraft is stalled
• FIRST: AoA MUST BE REDUCED• Release back pressure on stick or column
• Nose down pitch input may be needed
Note : Increasing thrust has an adverse effect on AoA reduction for Aircraft with engines below aircraft CG
• SECOND: If speed needs to be recovered• When stall indications cease, increase thrust with care due to
possible pitch up effect
AoA comes first, speed second
Page 9
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
A380 Stall in flight testMay 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Approach to Stall v/s Stall
Approach to Stall
• Stall indications already presentArtificial stall warningsSome natural stall warning indications may be present
• Progressive airflow separation
• Trajectory controllable with decreasing margin for manoeuvring
Page 11
Stall
• Stall indications Artificial stall warningsNatural stall warnings
BuffetingLack of pitch authorityLack of Roll controlInability to arrest descent
• Airflow separated from wing
• Trajectory no longer controllable
The change from approach to stall v/s actual stall is not easy to determine, even for a specialist.
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Approach to Stall v/s Stall recovery procedure
• The classic recovery procedure associated with “Approach to stall” was characterized by a recovery focusing on:
Maximum thrust application
Minimum loss of altitude
• Whereas the recovery procedure from an “Actual stall” has always focused on:
AoA reduction as first action, followed by a speed recovery if needed
Page 12
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Need for procedure change• Drawbacks associated with this dual recovery approach are:
TOGA application may lead to an increase of the AoAReluctance to apply nose down inputChallenge to identify the change from “Approach to stall” to “Actual stall”
• Numerous accidents where the “Approach to Stall” recovery procedurewas applied whereas the aircraft was actually stalledor generated a stall through thrust effect
Page 13
A single procedure focusing on AoA reduction, as a first action, required to cover both
the “Approach to Stall” and the “Actual Stall” recovery:
It is called the “Stall Recovery” procedure
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Contents
May 201117th Performance and Operations Conference
Stall phenomenon1
AoA control2
Stall recovery3
New procedure4
Conclusion5
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
New Procedure
•The FAA Stall Recovery Working Group issued a generic “Stall Recovery” procedure • A generic procedure for ALL types of aircraft
• One single procedure to cover ALL stall conditions
• Prevent full thrust/TOGA from being first action
• Focus on AoA reduction
Page 15
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Generic Stall Recovery Procedure
STALL WARNING OR AERODYNAMIC STALL RECOVERY PROCEDURE
Immediately do the following at the first indication of stall (buffet, stick shaker, stick pusher, or aural or visual indication) during any flight phases except at lift off.
1. Autopilot and autothrottle…………………………….…… Disconnect
Rationale: While maintaining the attitude of the aircraft, disconnect the autopilot and autothrottle. Ensure the pitch attitude does not change adversely when disconnecting the autopilot. This may be very important in mis-trim situations. Manual control is essential to recovery in all situations. Leaving one or the other connected may result in in-advertent changes or adjustments that may not be easily recognized or appropriate, especially during high workload situations.
Page 16
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Generic Stall Recovery Procedure
2. a) Nose down pitch control… Apply until out of stall (no longer have stall indications)b) Nose down pitch trim…….………………………………………..As needed
Rationale: a) The priority is reducing the angle of attack. There have been numerous situations where flight crews did not prioritize this and instead prioritized power and maintaining altitude. This will also address autopilot induced full back trim.
b) If the control column does not provide the needed response, stabilizer trim may be necessary. However, excessive use of trim can aggravate the condition, or may result in loss of control or in high structural loads.
3. Bank………………………….…………………………………….….Wings Level
Rationale: This orientates the lift vector for recovery.
Page 17
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Generic Stall Recovery Procedure
4. Thrust ……………………………………………………………….. As Needed
Rationale: During a stall recovery, many times maximum power is not needed. When stalling, the thrust can be at idle or at high thrust, typically at high altitude. Therefore, the thrust is to be adjusted accordingly during the recovery. For engines installed below the wing, applying maximum thrust can create a strong nose up pitching moment, if speed is low. For aircraft with engines mounted above the wings, thrust application creates a helpful pitch down tendency. For propeller driven aircraft, thrust application energizes the air flow around the wing, assisting in stall recovery.
5. Speed Brakes…………………….………………………………………. Retract
Rationale: This will improve lift and stall margin.
6. Return to the desired flight path.
Rationale: Apply gentle action for recovery to avoid secondary stalls then return to desired flight path.
Page 18
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Contents
May 201117th Performance and Operations Conference
Stall phenomenon1
AoA control2
Stall recovery3
New procedure4
Conclusion5
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
Conclusion
•Working together with other aircraft manufacturers, we have:
Agreed the principle with the FAA Stall Recovery Working GroupIssued a harmonized procedure focusing on AoAreduction as a first action
•The procedure was published mid-May 2010 and the corresponding FCTM end of May 2010.
Page 20
May 201117th Performance and Operations Conference
© AIRBUS S.A.S. All rights reserved. Confidential and proprietary document.
May 201117th Performance and Operations Conference
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