Its well known that the French investigation is focused on avoiding any allocation of blame. With all the inter-linkages between Airbus, Air France and the French government it is clear that the BEA is actually investigating the French government. The level of disclosure tolerated by the French is abysmally low in comparison to what the NTSB would be revealing.
The above paragraph from an earlier posting on this blog is being repeated in response to some inquiries I've had regarding the recent publication of more complete transcripts in a book that focuses clearly on pilot error and pilot standards.
The French view is that only pertinent conversations get published. The American view is that everything, including the final expletives, get published. It is a question of openness and a dedication to seeing that absolutely nothing is to prevent the deaths that have taken place from being deaths that contribute to future air safety.
There are serious issues as to whether the initial climb was the result of pilot commanded inputs or not. The book fails to address this issue. The fact that irrelevant conversations were taking place is meaningless. The plane was not at an altitude where rules impose a "sterile cockpit" devoid of non-pertinent conversations or activities.
The pilots were suddenly confronted with a situation where the computer suddenly said "your plane". As young pilots with an instructor beside them they've heard that phrase a zillion times but suddenly they are "hearing" it without warning and they are no longer in some small two-seated training aircraft. The computer gave up when limits were exceeded and dumped them into alternate law amidst a flurry of warning messages and loss of instruments coupled with loss of any sense that remaining instruments were or even might be reliable. Its pure hell when a complex system cuts out.
Other, non fatal, incidents indicate a serious likelihood that that initial climb of a few thousand feet was not selected by pilot initiated control inputs. After that the cascade of events proceeds with confusion and unreliable information. The start of the fatal event was that initial climb. Blame the pilots for it? Not yet!!!
Showing posts with label control surfaces. Show all posts
Showing posts with label control surfaces. Show all posts
Friday, October 14, 2011
Tuesday, April 12, 2011
AF447 and the One Legged Stool
I have long been a believer in the one-legged stool theory of aviation safety. Now, I know have very few readers but since some are not in the USA let me set forth with some particularity what a one-legged stool is. Most stools have three legs and are therefore quite stable when someone sits on them. A stool with one leg allows a person to sit on it and rest just as much but does require that he remain alert. Drifting off to sleep on a three legged stool can be easy. Drifting off to sleep while on a one legged stool is just as simple but has obvious consequences: you fall and that wakes you up.
One consequence of the ultra reliability of any electrical system is that monitoring it becomes so very boring. The aircraft systems are reliable. If something fails, there is a primary backup, if that fails there is a secondary backup, etc. It is so very boring. The Fly By Wire takes this even one step further and declares that the computers are so reliable that they should even be able to override pilot input since pilots are less reliable. Only in Alternate Law Mode does the computer surrender control of the airplane to the pilot and even that is done piecemeal with only certain systems surrendered to pilot control during the various Alternate Law modes.
But what about the Pilot's mode? Pilots have various modes too. Alert, drowsy, asleep, "in the loop", "out of the loop", etc. Qantas used to force pilots to work out a position report using pen and paper rather than simply pressing a button. This would keep the pilots mentally in the loop should trouble occur. We all know that on long flights there are a variety of breaks some of which are mandatory and some of which are optional.
Physical presence on the flight deck is one thing. Mental presence is another. A pilot who is sleeping in the cockpit or merely dozing there requires some time to get back into the loop.
Some have alleged that failure to deviate around weather indicates a dozing flight crew. All we can really say is that we have no indication that the pilots were in their seats and alert. We have some indications that fatigue may have overcome a sole occupant of the cockpit. While we can think that a pilot would not nap as the plane was penetrating the convergence zone it is possible and he might have asked to be roused and the pilot who was to have him awakened fell asleep.
Dealing with suddenly being dumped into Alternate Law Mode is difficult when the pilot is awake and fully aware of his situation. If a stall developed we all wonder why but mostly we wonder why was there no reaction to it. After all, by the third lesson student pilots are practicing stalls and having it drummed into them to lower the nose instantly and add power instantly. Nothing about that changes as one progresses from student pilot in a Cessna 172 to the left-seat of a multi-engined airliner. What changes is the excitement. A student pilot on his third lesson is "in the loop". He has full situational awareness. The professional pilot in an airliner has thousands of hours of sitting there punching buttons into a computer that does the flying. Its boring. We need to bring back that one-legged stool. Keep the pilots from getting complacent.
We all wonder how the airframe could become involved in a deep stall but the question that also must be addressed is how did it all begin. If it takes too long to wake up and gain situational awareness, a brief nap can be fatal. Airline pilots really do not practice stalls. They practice approaches to stalls. Once the airspeed deteriorated and a stall started to develop action can be taken. Once a stall is fully developed and the plane is in a deep stall wherein control surfaces are functionally ineffective there is far less that can be done and the pilot is in unknown territory. It is possible the pilot woke up to a nightmare. Often an instructor will have a student practice suddenly being required to select an emergency landing zone and make the approach to a landing in some pasture rather than on an airport runway. The practice usually ends just above the farmer's field but a good instructor will sometimes actually have a student make such a landing. A recently awakened pilot might not have been able to cope with a deep stall because he had only been given simulator time for an approach to a stall. There is no Emergency Checklist for a deep stall. You either know what to do or you don't. It either works or it doesn't. There is no time to do aught but act. If there was a double flame-out (doubtful) differential thrust could not be used.
One consequence of the ultra reliability of any electrical system is that monitoring it becomes so very boring. The aircraft systems are reliable. If something fails, there is a primary backup, if that fails there is a secondary backup, etc. It is so very boring. The Fly By Wire takes this even one step further and declares that the computers are so reliable that they should even be able to override pilot input since pilots are less reliable. Only in Alternate Law Mode does the computer surrender control of the airplane to the pilot and even that is done piecemeal with only certain systems surrendered to pilot control during the various Alternate Law modes.
But what about the Pilot's mode? Pilots have various modes too. Alert, drowsy, asleep, "in the loop", "out of the loop", etc. Qantas used to force pilots to work out a position report using pen and paper rather than simply pressing a button. This would keep the pilots mentally in the loop should trouble occur. We all know that on long flights there are a variety of breaks some of which are mandatory and some of which are optional.
Physical presence on the flight deck is one thing. Mental presence is another. A pilot who is sleeping in the cockpit or merely dozing there requires some time to get back into the loop.
Some have alleged that failure to deviate around weather indicates a dozing flight crew. All we can really say is that we have no indication that the pilots were in their seats and alert. We have some indications that fatigue may have overcome a sole occupant of the cockpit. While we can think that a pilot would not nap as the plane was penetrating the convergence zone it is possible and he might have asked to be roused and the pilot who was to have him awakened fell asleep.
Dealing with suddenly being dumped into Alternate Law Mode is difficult when the pilot is awake and fully aware of his situation. If a stall developed we all wonder why but mostly we wonder why was there no reaction to it. After all, by the third lesson student pilots are practicing stalls and having it drummed into them to lower the nose instantly and add power instantly. Nothing about that changes as one progresses from student pilot in a Cessna 172 to the left-seat of a multi-engined airliner. What changes is the excitement. A student pilot on his third lesson is "in the loop". He has full situational awareness. The professional pilot in an airliner has thousands of hours of sitting there punching buttons into a computer that does the flying. Its boring. We need to bring back that one-legged stool. Keep the pilots from getting complacent.
We all wonder how the airframe could become involved in a deep stall but the question that also must be addressed is how did it all begin. If it takes too long to wake up and gain situational awareness, a brief nap can be fatal. Airline pilots really do not practice stalls. They practice approaches to stalls. Once the airspeed deteriorated and a stall started to develop action can be taken. Once a stall is fully developed and the plane is in a deep stall wherein control surfaces are functionally ineffective there is far less that can be done and the pilot is in unknown territory. It is possible the pilot woke up to a nightmare. Often an instructor will have a student practice suddenly being required to select an emergency landing zone and make the approach to a landing in some pasture rather than on an airport runway. The practice usually ends just above the farmer's field but a good instructor will sometimes actually have a student make such a landing. A recently awakened pilot might not have been able to cope with a deep stall because he had only been given simulator time for an approach to a stall. There is no Emergency Checklist for a deep stall. You either know what to do or you don't. It either works or it doesn't. There is no time to do aught but act. If there was a double flame-out (doubtful) differential thrust could not be used.
Tuesday, April 5, 2011
Undercarriage lowered on AF447?
Even though Phase 4 is still underway and the FDR and CVR have not been located, it seems the suspense is growing. A very small debris field, high vertical descent component suspected. Did the crew fixate on a problem and not realize they were in a gentle descent? Or did they attempt to increase drag by lowering the undercarriage? Why would they attempt such a thing? I just can't wait for the Flight Data Recorder to be recovered and analyzed, though I don't know how complete the information would be. Its possible that the data was changing so rapidly the recording of averages will be deceptive.
It just doesn't seem reasonable that the pilots would descend all the way from Level 35 to sea level without realizing they were descending, no matter how fixated on some other item they might have been. Also during any such gentle descent, the lateral travel from the LKP would be greater no matter what the direction of that travel was, even if they did a 180 whether it be intentionally or by happenstance. Being dumped into Alternate Law mode suddenly and losing so many instruments without warning may have overloaded the crews ability to cope with sensory input, but the plane would travel in some direction even if they lost engines.
I had thought a deep stall but this appears to be so very unlikely since it is not known how to put that plane into a deep stall and yet have it strike the water in a mainly downward direction consistent with a flat spin. So perhaps the answer is simply that there was no flat spin. Yet extending the undercarriage would indicate pilot attention and desperation. It would also indicate an over speed condition, not an under speed condition, though it is possible that a desperate crew could have extended the gear even if the airspeed was minimal simply as an attempt to lower the nose to re-stablish laminar flow over the wing and gain an attitude wherein an engine re-start might take place. However, I do think that only impact forces affected the main landing gear and the main landing gear doors. I doubt there was any inflight attempt to lower the landing gear.
Some are focusing on WX and pilot induced oscillations leading to a loss of longitudinal dynamic stability so that the plane was tail heavy and both engines had flamed out. No control surfaces effective, no way to restart, not much flight from LKP, high vertical component, low horizontal one. Not a good situation to be in at all and certainly not at night while inside a thunderstorm. Of course the problem is that other aircraft flew pretty much the same track not long before and not long after AF447 and had no problems at that flight level. So while its hard to imagine longitudinal stability problems its sort of harder to imagine anything else.
If the initial data from the iced pitot tube resulted in the throttles being retarded sufficiently to induce an underspeed stall and that stall progressed to a fully stalled situation with the nose down sixty degrees and neither the wings nor the horizontal stabilizer generating lift it is possible that leading edge vortexes impinged on the vertical stabilizer. Such vortexes when combined with commanded inputs from a desperate flight crew could result in a catastrophic failure at altitude but I would expect the fuselage to impact in a more vertical rather than horizontal attitude. So it seems that the vertical stabilizer did indeed remain attached until impact.
At impact the transmission would cease but the intermittent interruptions in the ACARS transmissions and unavailability of the signal is thought by some to have been caused by the antenna being occluded by an inverted fuselage but this is undetermined.
It just doesn't seem reasonable that the pilots would descend all the way from Level 35 to sea level without realizing they were descending, no matter how fixated on some other item they might have been. Also during any such gentle descent, the lateral travel from the LKP would be greater no matter what the direction of that travel was, even if they did a 180 whether it be intentionally or by happenstance. Being dumped into Alternate Law mode suddenly and losing so many instruments without warning may have overloaded the crews ability to cope with sensory input, but the plane would travel in some direction even if they lost engines.
I had thought a deep stall but this appears to be so very unlikely since it is not known how to put that plane into a deep stall and yet have it strike the water in a mainly downward direction consistent with a flat spin. So perhaps the answer is simply that there was no flat spin. Yet extending the undercarriage would indicate pilot attention and desperation. It would also indicate an over speed condition, not an under speed condition, though it is possible that a desperate crew could have extended the gear even if the airspeed was minimal simply as an attempt to lower the nose to re-stablish laminar flow over the wing and gain an attitude wherein an engine re-start might take place. However, I do think that only impact forces affected the main landing gear and the main landing gear doors. I doubt there was any inflight attempt to lower the landing gear.
Some are focusing on WX and pilot induced oscillations leading to a loss of longitudinal dynamic stability so that the plane was tail heavy and both engines had flamed out. No control surfaces effective, no way to restart, not much flight from LKP, high vertical component, low horizontal one. Not a good situation to be in at all and certainly not at night while inside a thunderstorm. Of course the problem is that other aircraft flew pretty much the same track not long before and not long after AF447 and had no problems at that flight level. So while its hard to imagine longitudinal stability problems its sort of harder to imagine anything else.
If the initial data from the iced pitot tube resulted in the throttles being retarded sufficiently to induce an underspeed stall and that stall progressed to a fully stalled situation with the nose down sixty degrees and neither the wings nor the horizontal stabilizer generating lift it is possible that leading edge vortexes impinged on the vertical stabilizer. Such vortexes when combined with commanded inputs from a desperate flight crew could result in a catastrophic failure at altitude but I would expect the fuselage to impact in a more vertical rather than horizontal attitude. So it seems that the vertical stabilizer did indeed remain attached until impact.
At impact the transmission would cease but the intermittent interruptions in the ACARS transmissions and unavailability of the signal is thought by some to have been caused by the antenna being occluded by an inverted fuselage but this is undetermined.
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