Different types of stall?
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Different types of stall?
As I understand it, stall refers to the near absence of lift generation by the wings, resulting in the aircraft losing height quickly, if not recovered.
Does the recovery procedure vary by the cause of the stall?
Specifically, when the stall warning goes off due to mismatch between the airspeed bugs and the ref speeds switch, is the stall recovery procedure different?
Case in mind: Colgan Air Flight 3407, buffalo 2009
Does the recovery procedure vary by the cause of the stall?
Specifically, when the stall warning goes off due to mismatch between the airspeed bugs and the ref speeds switch, is the stall recovery procedure different?
Case in mind: Colgan Air Flight 3407, buffalo 2009
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you can stall with airspeed reading right. you can stall if the airspeed indicator is not working at all.
IT all depends on exceeding the critical angle of attack.
the recovery is always to reduce the angle of attack to below the critical angle of attack.
the control wheel controls angle of attack (most of the time). you increase angle of attack by pulling back, you reduce angle of attack by pushing forward.
therefore in most stalls pushing forward gets you out of the stall. exceptions might be in the aerobatic relm which I will not discuss here.
IT all depends on exceeding the critical angle of attack.
the recovery is always to reduce the angle of attack to below the critical angle of attack.
the control wheel controls angle of attack (most of the time). you increase angle of attack by pulling back, you reduce angle of attack by pushing forward.
therefore in most stalls pushing forward gets you out of the stall. exceptions might be in the aerobatic relm which I will not discuss here.
Stall is the condition of insufficient lift for the aircraft weight (mass at 1g) which is approximately the angle of attack which generates maximum lift. It can only be associated with speed for specific conditions (stall speed), but there is little point in using speed in understanding stalling and recovery.
Stall warning (before the stall) and identification (at the stall) are normally generated by angle of attack so the condition can be identified irrespective of manoeuvre, weight. There are also changes for configuration.
Conventional wing stall is usually separated into level flight or turning flight (accelerated stall), and in rare circumstances problems of transonic flight (shock stall), which should not have any significant affects for commercial aircraft due to certification requirements.
The stall condition can be affected by wing ice contamination and in general is only an issue if the anti-icing systems fail; although most modern aircraft will adjust the warnings when anti-icing systems are being used.
Wings can generate lift beyond the stall angle, but insufficient for level flight. The main problem in this region of flight is maintaining control, thus it is best avoided, where recovery is to reduce the AOA by moving the stick forward. In many commercial aircraft, or those with particular problems, stall identification is supplemented by a stick pusher to direct the pilot to the correct course of action.
The conditions beyond the stall AOA are referred to as ‘deep stall’ and often confused with 'locked in stall' which is normally reserved for situations where the elevator control becomes ineffective and the stall might be unrecoverable. Although not impossible, most commercial aircraft will not suffer from this. A similar condition can be encountered at AOAs greater than stall where the pitch control is held back (also depends on trim, cg), thus preventing a reduction in AOA, but with correct procedure the aircraft should recover.
Modern aircraft with electronically signalled controls avoid the stall by pitch-control (AOA) limiting or increasing control force, but have similar characteristics if aspects of the system fail.
Another form of stall is ‘tail stall’ which should not be associated with wing stall even though the aerodynamics of loss of lift is similar. Because tail lift acts opposite sense to the wing, the symptoms of and recovery actions for tail stall are totally different. Tail stall in normal flight conditions – not in icing, is extremely unlikely due to certification requirements.
Some aircraft in rare icing conditions – where the tail will accumulate ice more quickly than the wing, can suffer tail stall, but this too is minimised by certification, but not every icing condition can be specified.
Tail stall is normally associated with lowering flaps (at the higher end of the speed range) which demands more tail ‘down’ lift. If the tail lift is already reduced by ice then the lack of lift can result in an uncontrolled and often rapid nose-down pitch change.
Recovery action is aircraft type dependent, but generally involves a rapid and forceful back-stick input and raising flap.
The Colgan accident was associated with wing stall in icing conditions, but misidentified as tail stall (fatigue, recent training on tail stall, etc) where the recovery action taken was opposite to that required.
Stall warning (before the stall) and identification (at the stall) are normally generated by angle of attack so the condition can be identified irrespective of manoeuvre, weight. There are also changes for configuration.
Conventional wing stall is usually separated into level flight or turning flight (accelerated stall), and in rare circumstances problems of transonic flight (shock stall), which should not have any significant affects for commercial aircraft due to certification requirements.
The stall condition can be affected by wing ice contamination and in general is only an issue if the anti-icing systems fail; although most modern aircraft will adjust the warnings when anti-icing systems are being used.
Wings can generate lift beyond the stall angle, but insufficient for level flight. The main problem in this region of flight is maintaining control, thus it is best avoided, where recovery is to reduce the AOA by moving the stick forward. In many commercial aircraft, or those with particular problems, stall identification is supplemented by a stick pusher to direct the pilot to the correct course of action.
The conditions beyond the stall AOA are referred to as ‘deep stall’ and often confused with 'locked in stall' which is normally reserved for situations where the elevator control becomes ineffective and the stall might be unrecoverable. Although not impossible, most commercial aircraft will not suffer from this. A similar condition can be encountered at AOAs greater than stall where the pitch control is held back (also depends on trim, cg), thus preventing a reduction in AOA, but with correct procedure the aircraft should recover.
Modern aircraft with electronically signalled controls avoid the stall by pitch-control (AOA) limiting or increasing control force, but have similar characteristics if aspects of the system fail.
Another form of stall is ‘tail stall’ which should not be associated with wing stall even though the aerodynamics of loss of lift is similar. Because tail lift acts opposite sense to the wing, the symptoms of and recovery actions for tail stall are totally different. Tail stall in normal flight conditions – not in icing, is extremely unlikely due to certification requirements.
Some aircraft in rare icing conditions – where the tail will accumulate ice more quickly than the wing, can suffer tail stall, but this too is minimised by certification, but not every icing condition can be specified.
Tail stall is normally associated with lowering flaps (at the higher end of the speed range) which demands more tail ‘down’ lift. If the tail lift is already reduced by ice then the lack of lift can result in an uncontrolled and often rapid nose-down pitch change.
Recovery action is aircraft type dependent, but generally involves a rapid and forceful back-stick input and raising flap.
The Colgan accident was associated with wing stall in icing conditions, but misidentified as tail stall (fatigue, recent training on tail stall, etc) where the recovery action taken was opposite to that required.
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Originally Posted by PEI 3721
The Colgan accident was associated with wing stall in icing conditions, but misidentified as tail stall (fatigue, recent training on tail stall, etc) where the recovery action taken was opposite to that required.
I would encourage anyone who might have the wrong impression of the flight conditions, the susceptibility of the Q400, and/or the actions taken by the flight crew to read the “Official” NTSB accident report – it’s easy to find on the NTSB website:
https://www.ntsb.gov/investigations/...y/AAR1001.html
And it includes the following quotes under “Findings” –
NTSB Findings:
The captain’s inappropriate aft control column inputs in response to the stick shaker caused the airplane’s wing to stall.
The minimal aircraft performance degradation resulting from ice accumulation did not affect the flight crew’s ability to fly and control the airplane.
Explicit cues associated with the impending stick shaker onset, including the decreasing margin between indicated airspeed and the low-speed cue, the airspeed trend vector pointing downward into the low-speed cue, the changing color of the numbers on the airplane’s indicated airspeed display, and the airplane’s excessive nose-up pitch attitude, were presented on the flight instruments with adequate time for the pilots to initiate corrective action, but neither pilot responded to the presence of these cues.
The reason the captain did not recognize the impending onset of the stick shaker could not be determined from the available evidence, but the first officer’s tasks at the time the low-speed cue was visible would have likely reduced opportunities for her timely recognition of the impending event; the failure of both pilots to detect this situation was the result of a significant breakdown in their monitoring responsibilities and workload management.
The flight crew did not consider the position of the reference speeds switch when the stick shaker activated.
The captain’s response to stick shaker activation should have been automatic, but his improper flight control inputs were inconsistent with his training and were instead consistent with startle and confusion.
The captain did not recognize the stick pusher’s action to decrease angle-of-attack as a proper step in a stall recovery, and his improper flight control inputs to override the stick pusher exacerbated the situation.
It is unlikely that the captain was deliberately attempting to perform a tailplane stall recovery.
No evidence indicated that the Q400 was susceptible to a tailplane stall.
The flight crewmembers’ performance during the flight, including the captain’s deviations from standard operating procedures and the first officer’s failure to challenge these deviations, was not consistent with the crew resource management (CRM) training that they had received or the concepts in the Federal Aviation Administration’s CRM guidance.
The captain had not established a good foundation of attitude instrument flying skills early in his career, and his continued weaknesses in basic aircraft control and instrument flying were not identified and adequately addressed.
Remedial training and additional oversight for pilots with training deficiencies and failures would help ensure that the pilots have mastered the necessary skills for safe flight.
The current air carrier approach-to-stall training did not fully prepare the flight crew for an unexpected stall in the Q400 and did not address the actions that are needed to recover from a fully developed stall.
Probable Cause
The National Transportation Safety Board determines that the probable cause of this accident was the captain’s inappropriate response to the activation of the stick shaker, which led to an aerodynamic stall from which the airplane did not recover. Contributing to the accident were (1) the flight crew’s failure to monitor airspeed in relation to the rising position of the low- speed cue, (2) the flight crew’s failure to adhere to sterile cockpit procedures, (3) the captain’s failure to effectively manage the flight, and (4) Colgan Air’s inadequate procedures for airspeed selection and management during approaches in icing conditions.
The captain’s inappropriate aft control column inputs in response to the stick shaker caused the airplane’s wing to stall.
The minimal aircraft performance degradation resulting from ice accumulation did not affect the flight crew’s ability to fly and control the airplane.
Explicit cues associated with the impending stick shaker onset, including the decreasing margin between indicated airspeed and the low-speed cue, the airspeed trend vector pointing downward into the low-speed cue, the changing color of the numbers on the airplane’s indicated airspeed display, and the airplane’s excessive nose-up pitch attitude, were presented on the flight instruments with adequate time for the pilots to initiate corrective action, but neither pilot responded to the presence of these cues.
The reason the captain did not recognize the impending onset of the stick shaker could not be determined from the available evidence, but the first officer’s tasks at the time the low-speed cue was visible would have likely reduced opportunities for her timely recognition of the impending event; the failure of both pilots to detect this situation was the result of a significant breakdown in their monitoring responsibilities and workload management.
The flight crew did not consider the position of the reference speeds switch when the stick shaker activated.
The captain’s response to stick shaker activation should have been automatic, but his improper flight control inputs were inconsistent with his training and were instead consistent with startle and confusion.
The captain did not recognize the stick pusher’s action to decrease angle-of-attack as a proper step in a stall recovery, and his improper flight control inputs to override the stick pusher exacerbated the situation.
It is unlikely that the captain was deliberately attempting to perform a tailplane stall recovery.
No evidence indicated that the Q400 was susceptible to a tailplane stall.
The flight crewmembers’ performance during the flight, including the captain’s deviations from standard operating procedures and the first officer’s failure to challenge these deviations, was not consistent with the crew resource management (CRM) training that they had received or the concepts in the Federal Aviation Administration’s CRM guidance.
The captain had not established a good foundation of attitude instrument flying skills early in his career, and his continued weaknesses in basic aircraft control and instrument flying were not identified and adequately addressed.
Remedial training and additional oversight for pilots with training deficiencies and failures would help ensure that the pilots have mastered the necessary skills for safe flight.
The current air carrier approach-to-stall training did not fully prepare the flight crew for an unexpected stall in the Q400 and did not address the actions that are needed to recover from a fully developed stall.
Probable Cause
The National Transportation Safety Board determines that the probable cause of this accident was the captain’s inappropriate response to the activation of the stick shaker, which led to an aerodynamic stall from which the airplane did not recover. Contributing to the accident were (1) the flight crew’s failure to monitor airspeed in relation to the rising position of the low- speed cue, (2) the flight crew’s failure to adhere to sterile cockpit procedures, (3) the captain’s failure to effectively manage the flight, and (4) Colgan Air’s inadequate procedures for airspeed selection and management during approaches in icing conditions.
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Originally Posted by pei
The Colgan accident was associated with wing stall in icing conditions, but misidentified as tail stall
Originally Posted by NTSB
It is unlikely that the captain was deliberately attempting to perform a tailplane stall recovery.
No evidence indicated that the Q400 was susceptible to a tailplane stall.
No evidence indicated that the Q400 was susceptible to a tailplane stall.
The Captain lost awareness of excessive speed decay and just pulled back at the stall warning, historically a well-documented error.
BOAC, given that neither we nor the NTSB have knowledge of what the Colgan crew saw, deduced, or ‘deliberately’ reasoned before their actions, there will always be some speculation.
IMHO the NTSB place too much emphasis on what should have seen, monitored, etc; how can anyone know that speed awareness was poor or was there any bias in the reason to pull up – and if so was the bias a flaw in generic stall training or the effect of the crew’s recent (unwarranted) tail stall training.
The NTSB’s findings have the caveat of ‘most probable cause’; many accident investigators shy away from ‘cause’ which might incorrectly focus on one aspect. They also avoid or explain their use of ‘error’.
It would be better to consider the crew as an operational unit, their apparent joint behaviour and documented training history. Why did the PNF raise the flap and the PF pull back; together these appear to be better aligned with tail stall, which is why I used this accident as a simple example to distinguish between the types of stall, the recognition features, and actions required.
A tail stall will not give a stick shake alert (AFAIK), but did the crew know that.
NASA has produced a good training video of tail stall which is predominantly aimed at GA flying. Unfortunately many commercial training sessions take easily available off-the-shelf materials and use them without further thought as to their relevance to aircraft type or operation. Tail stall is now much less relevant to commercially certificated aircraft which have been subject to new rule making; the icing test requirements have been strengthened with considerable focus on conventional stalling and stall warning. AFAIR the Q400 had considered many of these aspects.
AFAIK the last commercial aircraft subject to tail icing was the J31; all of these aircraft were modified to restrict the configuration associated with the conditions; or has anyone more recent information.
IMHO the NTSB place too much emphasis on what should have seen, monitored, etc; how can anyone know that speed awareness was poor or was there any bias in the reason to pull up – and if so was the bias a flaw in generic stall training or the effect of the crew’s recent (unwarranted) tail stall training.
The NTSB’s findings have the caveat of ‘most probable cause’; many accident investigators shy away from ‘cause’ which might incorrectly focus on one aspect. They also avoid or explain their use of ‘error’.
It would be better to consider the crew as an operational unit, their apparent joint behaviour and documented training history. Why did the PNF raise the flap and the PF pull back; together these appear to be better aligned with tail stall, which is why I used this accident as a simple example to distinguish between the types of stall, the recognition features, and actions required.
A tail stall will not give a stick shake alert (AFAIK), but did the crew know that.
NASA has produced a good training video of tail stall which is predominantly aimed at GA flying. Unfortunately many commercial training sessions take easily available off-the-shelf materials and use them without further thought as to their relevance to aircraft type or operation. Tail stall is now much less relevant to commercially certificated aircraft which have been subject to new rule making; the icing test requirements have been strengthened with considerable focus on conventional stalling and stall warning. AFAIR the Q400 had considered many of these aspects.
AFAIK the last commercial aircraft subject to tail icing was the J31; all of these aircraft were modified to restrict the configuration associated with the conditions; or has anyone more recent information.
