Stall recovery training
Thread Starter
Join Date: Jun 2011
Location: Denison, TX
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Stall recovery training
A fallout of the stick shaker technique for windshear recovery was airline stall training to do a power off stall with a power on recovery while attempting to hold the pitch at the level of the initial stall. This technique was throughly disproven (1989) by the optimal trajectory studies of Professor Angelo Miele and the Aero-Astronautics Group of Rice University. Does any airline still teach this technique?
while attempting to hold the pitch at the level of the initial stall
Thread Starter
Join Date: Jun 2011
Location: Denison, TX
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for your response. Minimum height loss is what I am talking about. It came from a mistaken belief that aircraft performance for windshear encounters could be enhanced at high AOA. The last study in optimal trajectories (1989), done by Professor Angelo Miele and the Aero-Astronautics Group of Rice University showed that for both the takeoff and landing cases "Maintaining the aircraft at the stick shaker is a poor strategy in terms of altitude loss and survival capability." and "If the pilot accidentally or deliberately increases the angle of attack to the stick shaker value, follwing the windshear onset, the optimal recovery trajectory (ORT) requires that the angle of attack be reduced quickly to a lower value and then increased gradually in such a way that the stick shaker value is reached again near the end of the shear.", with substantiating proof that the ORT can recover from a windshear twice as strong as when a high AOA is maintained. Best performance for a jet aircraft occurs at the minimum drag point for the configuration. The pilot will not know when the shear ends, but should know where the ground begins and should not deliberately fly up the backside of the drag curve until ground impact is imminent.
The March 7, 2011 issue of AW&ST contains an article about several accidents where pilots (allegedly) kept an aircraft in a stall without recovering. This may be an effect of teaching pilots to fly at high AOA to minimize height loss instead or immediately recovering aerodynamic quality as they should have been taught in their first training flight.
The March 7, 2011 issue of AW&ST contains an article about several accidents where pilots (allegedly) kept an aircraft in a stall without recovering. This may be an effect of teaching pilots to fly at high AOA to minimize height loss instead or immediately recovering aerodynamic quality as they should have been taught in their first training flight.
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
I think any windshear procedure will inevitably be generic, and may prove a bad procedure in some cases.
I think that the whole idea of the stick shaker procedure is to try to minimize height loss while the windshear is worst. If you fly at lower and more efficien aoas you will lose altitude. Maybe the windshear will not last enough time to make the altitude loss worth it.
When the windshear finishes, and it always finishes, the airplane will fly at any angle of attack. But if the windshear is long and strong, it could be worth flying at the optimum aoa, or even retracting landing gear...
I think that the whole idea of the stick shaker procedure is to try to minimize height loss while the windshear is worst. If you fly at lower and more efficien aoas you will lose altitude. Maybe the windshear will not last enough time to make the altitude loss worth it.
When the windshear finishes, and it always finishes, the airplane will fly at any angle of attack. But if the windshear is long and strong, it could be worth flying at the optimum aoa, or even retracting landing gear...
In a downburst windshear the obvious objective close to the ground is to avoid hitting it!
For recovery at very low level without guidance, all of the aircraft’s excess energy should go into maximizing vertical performance without compromising control – turbulent situation. Thus, the technique of ‘respecting’ the stall warning; the airspeed is maintained at or just before the shaker (not flying continuously with the shaker on as the margin from a full stall is unknown).
As altitude increases (~ 500ft agl), then some energy can be used to leave the area by increasing speed.
Some windshear recovery guidance systems use this type of tradeoff, maximizing climb at low altitude, but commanding a higher speed as altitude increases. In some circumstances, during the approach, but generally at a reasonable altitude, the command could lower the nose to gain speed (increasing energy) before attempting to climb. This depends on aircraft type, configuration and energy capability.
An example of a successful unaided recovery – respecting the stall warning: Windshear Incident
The now ‘defunct’ ideas for recovery from stall warning / stall, involved muddled thinking; if the trainers did use aspects of the windshear recovery, then they forgot about the context of the event, particularly different altitudes and the range of excess energy that a particular aircraft might have. The crew might know the first, but perhaps not the second aspect.
For recovery at very low level without guidance, all of the aircraft’s excess energy should go into maximizing vertical performance without compromising control – turbulent situation. Thus, the technique of ‘respecting’ the stall warning; the airspeed is maintained at or just before the shaker (not flying continuously with the shaker on as the margin from a full stall is unknown).
As altitude increases (~ 500ft agl), then some energy can be used to leave the area by increasing speed.
Some windshear recovery guidance systems use this type of tradeoff, maximizing climb at low altitude, but commanding a higher speed as altitude increases. In some circumstances, during the approach, but generally at a reasonable altitude, the command could lower the nose to gain speed (increasing energy) before attempting to climb. This depends on aircraft type, configuration and energy capability.
An example of a successful unaided recovery – respecting the stall warning: Windshear Incident
The now ‘defunct’ ideas for recovery from stall warning / stall, involved muddled thinking; if the trainers did use aspects of the windshear recovery, then they forgot about the context of the event, particularly different altitudes and the range of excess energy that a particular aircraft might have. The crew might know the first, but perhaps not the second aspect.
Join Date: Mar 2006
Location: East of Eden
Posts: 101
Likes: 0
Received 0 Likes
on
0 Posts
Have a look at the latest Airbus Safety First magazine with an article on the latest stalling procedure.
http://www.ukfsc.co.uk/files/Safety%...ary%202011.pdf
http://www.ukfsc.co.uk/files/Safety%...ary%202011.pdf
Thread Starter
Join Date: Jun 2011
Location: Denison, TX
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
minimizing height loss
Your reply speaks directly to the issues which began in the 1970s with similar recommendations and resulted in the stall recovery procedure I am asking about. Faulty windshear models were used which saved the aircraft by holding altitude. The optimal trajectory studies clearly showed the best procedure when close to the ground at high AOA was to quickly regain flying quality by reducing AOA and then gradually increasing AOA as ground impact became imminent. The intensity of microbursts was greatly understated by NTSB and manufacturers, saying the pilots must have done someting wrong.
Although the optimal trajectory sltudies (funded by NASA Langley, Boeing, the state of Texas and ALPA) proved the best technique for surviving a strong microburst at low altitude, the major reason we don't see the accidents today is that finally the industry was convienced how strong they can be and pilots have learned to be afraid of them. Before, only bad pilots crashed in microbursts so those of us with the right stuff did not have to worry.
The issue now is, does the practice of minimizing altitude loss (at the cost of sacrificing aerodynamic flying quality) by demonstrating power off stalls with power on recovery still exist? In the worst case example (low altitude strong microburst) the stall will not be power off and this technique can lead to disaster. The suggestion of maintaing a high AOA was clearly proven wrong over 20 years ago.
Also, there is a relatively unknown problem of Dynamic Stall, identified by S.S. Hoerner in his book on Fluid Dynamics, where the AOA at which the airflow re-attaches to the upper surface of the wing can be considerably less than the AOA at initial stall.
Although the optimal trajectory sltudies (funded by NASA Langley, Boeing, the state of Texas and ALPA) proved the best technique for surviving a strong microburst at low altitude, the major reason we don't see the accidents today is that finally the industry was convienced how strong they can be and pilots have learned to be afraid of them. Before, only bad pilots crashed in microbursts so those of us with the right stuff did not have to worry.
The issue now is, does the practice of minimizing altitude loss (at the cost of sacrificing aerodynamic flying quality) by demonstrating power off stalls with power on recovery still exist? In the worst case example (low altitude strong microburst) the stall will not be power off and this technique can lead to disaster. The suggestion of maintaing a high AOA was clearly proven wrong over 20 years ago.
Also, there is a relatively unknown problem of Dynamic Stall, identified by S.S. Hoerner in his book on Fluid Dynamics, where the AOA at which the airflow re-attaches to the upper surface of the wing can be considerably less than the AOA at initial stall.
The issue now is, does the practice of minimizing altitude loss (at the cost of sacrificing aerodynamic flying quality) by demonstrating power off stalls with power on recovery still exist?
I am busy with my initial B738 rating.
What attitude do I have to fly for an approach to stall exercise in order to maintain
10 000 feet? We are not allowed to lose any height during the exercise.Ground contact is an factor.. During my first attempt I fell out of the sky like a ton of bricks!
What attitude do I have to fly for an approach to stall exercise in order to maintain
10 000 feet? We are not allowed to lose any height during the exercise.Ground contact is an factor.. During my first attempt I fell out of the sky like a ton of bricks!
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 82
Posts: 1,454
Likes: 0
Received 0 Likes
on
0 Posts
To put this thread in context. Probably the classic downburst accident, Delta Flt 191.
http://www.airdisaster.com/reports/ntsb/AAR86-05.pdf
The PF control inputs initially were good, but then he started to push the nose down to avoid stick shaker.
The CVR recordings are available online in a number of formats.
I think I would have just set ~7 degrees nose up and set max thrust and ignored the stick shaker once go around was decided.
I was discussing this accident with someone else, as an example of task saturation.
As a Naval Aviator, this approach seems (to me) to have a lot in common with a night approach to the ship. Of course, over the quarter century since I last read the accident report, I had confused the aircraft type and airline, but the inexplicable nose down inputs have stayed engraved in my brain.
Since the northern hemisphere is moving into Summer, this is probably a timely topic.
Note: The airdisaster.com website has been very very slow. Try to be patient with it.
http://www.airdisaster.com/reports/ntsb/AAR86-05.pdf
The PF control inputs initially were good, but then he started to push the nose down to avoid stick shaker.
A control column force analysis performed by Lockheedshowed that a 22-pound push force was applied to the control column about 12 seconds before initial touchdown. Over the next 4 seconds, the forces were reversed, and by 8 seconds before impact, a 25 pound pull force was being exerted. Overthe next 7 seconds, the forces again reversed and by 1 second before impact a lo-pound push force was being applied. Duringthe last second the push force was decreasing.
I think I would have just set ~7 degrees nose up and set max thrust and ignored the stick shaker once go around was decided.
I was discussing this accident with someone else, as an example of task saturation.
As a Naval Aviator, this approach seems (to me) to have a lot in common with a night approach to the ship. Of course, over the quarter century since I last read the accident report, I had confused the aircraft type and airline, but the inexplicable nose down inputs have stayed engraved in my brain.
Since the northern hemisphere is moving into Summer, this is probably a timely topic.
Note: The airdisaster.com website has been very very slow. Try to be patient with it.
Last edited by Machinbird; 5th Jun 2011 at 05:08. Reason: add control input paragraph/remark on airdisaster.com site
Thread Starter
Join Date: Jun 2011
Location: Denison, TX
Posts: 10
Likes: 0
Received 0 Likes
on
0 Posts
Delta 191 control column push
Control column forces are not recorded on an L-1011. There is no way to conclude what it could have been without using measured control surface position and backtracking with numerous assumptions in a very dynamic environment. It is a thin thread to hang an argument on compared to hundreds of optimal trajectories to find the very best that can be done in a defined windshear with a defined aircraft. Then, knowing the very best, comparisons were made to other recommencations to see how well they performed. The maximum angle of attack trajectory performed very poorly.
My question has been answered as it now appears that some airlines are teaching the power off stall with power on recovery while keeping a high AOA to minimize altitude loss. In my opinion, this came from the stick shaker technique for wind shear recovery and is a very dangerous technique unless ground impact is imminent (like radar altitude less than 100 feet). Not only is flight path perfomance considerably degraded with the high drag, but there is the danger of a dynamic stall; the stall in the worst case will be power on and there is inadequate instrumentation. The question is: are the stall related accidents which the industry is now concerned with, related to stall recovery training?
Contrary to poplular opinion, transport aircraft are not required to have the stick shaker activate at 7% above a 1g stall, but 7% above Vmin which was allowed to be less than a 1g stall. This was an issue in the Congressonally mandated National Research Council study on windshear after the 1982 Pan American crash in New Orleans. That report (Library of Congress no. 83-63100) says on page 63 "The minimum speed at which level flight can be sustained is the 1g stall speed (Vmin 1g), which is typically 5 to 7 percent faster than the FAR stall speed."
My question has been answered as it now appears that some airlines are teaching the power off stall with power on recovery while keeping a high AOA to minimize altitude loss. In my opinion, this came from the stick shaker technique for wind shear recovery and is a very dangerous technique unless ground impact is imminent (like radar altitude less than 100 feet). Not only is flight path perfomance considerably degraded with the high drag, but there is the danger of a dynamic stall; the stall in the worst case will be power on and there is inadequate instrumentation. The question is: are the stall related accidents which the industry is now concerned with, related to stall recovery training?
Contrary to poplular opinion, transport aircraft are not required to have the stick shaker activate at 7% above a 1g stall, but 7% above Vmin which was allowed to be less than a 1g stall. This was an issue in the Congressonally mandated National Research Council study on windshear after the 1982 Pan American crash in New Orleans. That report (Library of Congress no. 83-63100) says on page 63 "The minimum speed at which level flight can be sustained is the 1g stall speed (Vmin 1g), which is typically 5 to 7 percent faster than the FAR stall speed."
Join Date: Aug 2008
Location: Betwixt and between
Posts: 666
Likes: 0
Received 0 Likes
on
0 Posts
My question has been answered as it now appears that some airlines are teaching the power off stall with power on recovery while keeping a high AOA to minimize altitude loss.
For an actual stall, the advice is and was to maintaining a nose down attitude until the stick shaker stops. Recently, the stall recovery manoeuvre was changed to also incorporate stall to approach so that in either case the first action should be to select a lower nose attitude.
