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.
Showing posts with label Overspeed. Show all posts
Showing posts with label Overspeed. Show all posts
Tuesday, April 5, 2011
Wednesday, February 16, 2011
AF 447 Air France flight lost over the Atlantic
I just learned that NOVA will have a special tonight on the AF 447 flight. There are so many interesting aspects to this puzzle. Primary amongst them is the Airbus concept of a computer flying the aircraft and over-riding pilot input in certain modes. Also involved are sensor design issues, conflicting data resolution issues, pilot attention issues, international cooperation issues, search operations issues and use of maintenance data as an alternative to the unrecovered Black Boxes.
I'm uncertain if the plane deviated for severe weather or not. I think the primary problem was overspeed resulting in a deep stall at high altitude resulting in a near vertical descent with little forward speed. It would be a problem of how to evaluate fluctuating data from multiple sensors.
The flight into a severe thunderstorm may well have taken place although the pilots may have believed they were above the storm. In most stalls the rule is simple: lower the nose immediately and add power immediately. This simple rule usually results in greater air flow over the wings to generate lift. Wings are usually designed to stall from the inboard area first so that the pilot has time to react before the stall reaches the outboard areas of the wing and the control surfaces become stalled. In a deep stall, moving the control surfaces has no effect because there is no airflow over the control surfaces. Adding power may be a problem if there was a sudden and unexpected ingestion of super-cooled rainwater into the engines. If it was not just pitot tube icing but an engine flame-out, no power may have been available to the pilots even if in their information overload state of mind they realized they desperately needed to add power.
Analysis of the flight from the ACARS maintenance data transmissions is not ideal. The information is designed to give maintenance crews an indication of what systems will need to be tested when the plane lands and what tools and parts should be on hand for the task. Such maintenance data is not an alternative to a Flight Data Recorder. There are also problems since the ACARS messages are held in a one minute suspense window and are grouped by item and priority. Certain message evaluation rules are clearly compromises. A fault detected by a system is considered more serious if it relates to a separate system than if it is a self-detected internal fault. A fault is deemed to be hard if it persists for thirty seconds whereas a fault is deemed soft if it is detected for less than thirty seconds. Such rules do make sense in most circumstances.
The loss of satellite uplink carrier signal during a critical time is one argument against replacing physical black boxes with constant electronic transmission of the FDR and CVR data. The cost of such transmissions is a major problem also.
I'm sure it will be an interesting program and I look forward to viewing it. I hope all my many readers (LOL) will enjoy it.
By the way, the most relevant incident to compare AF447 with is the Gimli Glider incident. That plane ran out of fuel half way through its flight and all the design errors, pilot errors and ATC errors were countered by one thing alone, pilot expertise. The pilot had a hobby of flying gliders, so when he suddenly found himself flying a huge ungainly glider full of passengers, he still knew what to do and how to do it. He had flown gliders before. He knew to make his S turns toward his objective and not lose sight of it. He knew how to do skids. He was flying the airplane rather than monitoring computers but everything turned out okay because he was used to actually flying the airplane rather than monitoring computers. That is a rare skill nowadays.
With AF447 when things turned so bad that the computer entered Alternate Law mode the computer would no longer override disapproved pilot inputs and would allow the pilots to fly the aircraft as they saw fit. Unfortunately, the pilots were not very experienced at actually flying the aircraft and were not able to do it in situations of high informational overload, high insecurity as to the reliability of their instruments and unusual attitudes. When Fly-By-Wire ended and Alternate Law started, the situation was already critical and the pilots desperately needed a learning curve. Unfortunately, there is no learning curve during such an event. If you've entered even the fringes of a supercell at night and are experiencing electrical overloads, have circuit breakers popping all over the place, are losing some instruments and have utterly lost faith in all your instruments, the situation is hopeless for a pilot who really doesn't know how to fly an airplane without a computer.
Every flight using a computer to change altitude saves on fuel costs over a heavy handed pilot trying to manipulate the throttles, but every such flight deprives the pilot of real flying experience. Just as the Gimli Glider incident involved a sudden transition the AF447 undoubtedly involved a sudden transition even though we don't know the cause. Initial lightning seems insufficient. Iced-up pitot sensors can have any number of causes. Auto Pilot and Auto Thrust are different systems and some confusion may have existed as to speed selection and the rapidity of speed adjustment attempts that were required.
If there was a deep stall, I just wonder what attitude is required for it. Note: A Deep Stall is one wherein no manipulation of power or control surfaces will have sufficient effect. A pilot in the deep stalled plane is as utterly helpless as a pilot on the ground who might be observing the incident. The pilot on the ground will push a non existent throttle lever, the pilot in the plane will push an actual throttle lever however the effect will be the same. A pilot on the ground will push an imaginary steering yoke, a pilot in the plane will push a real steering yoke yet the results will be the same. No effect whatsoever. A deep stall with or without a flat spin would mean a high speed vertical descent with little forward momentum.
NOTE: On Feb 28 2011, the Alucia arrived, fresh from a Seattle overhaul, at the Pacific waiting area for transiting the Panama Canal to begin its three phase search for the Black Boxes using remote controlled submersibles.
NOTE: This Phase 4 search continues. IF there is a Phase 5, Recovery Phase, a different ship and different equipment will be used. So far, no debris field has been discovered much less the "black boxes". (April 2nd, 2011).
Debris Field found. Learmount of Flight International being quoted on theory of crew fatigue induced fixation on minor problem while plane was in an unnoticed gentle descent resulting in a collision of an intact and controllable plane with the sea. He does not believe there was any deep stall. Merely pilots having lost so many instruments that they did not believe what few instruments remained.
I'm uncertain if the plane deviated for severe weather or not. I think the primary problem was overspeed resulting in a deep stall at high altitude resulting in a near vertical descent with little forward speed. It would be a problem of how to evaluate fluctuating data from multiple sensors.
The flight into a severe thunderstorm may well have taken place although the pilots may have believed they were above the storm. In most stalls the rule is simple: lower the nose immediately and add power immediately. This simple rule usually results in greater air flow over the wings to generate lift. Wings are usually designed to stall from the inboard area first so that the pilot has time to react before the stall reaches the outboard areas of the wing and the control surfaces become stalled. In a deep stall, moving the control surfaces has no effect because there is no airflow over the control surfaces. Adding power may be a problem if there was a sudden and unexpected ingestion of super-cooled rainwater into the engines. If it was not just pitot tube icing but an engine flame-out, no power may have been available to the pilots even if in their information overload state of mind they realized they desperately needed to add power.
Analysis of the flight from the ACARS maintenance data transmissions is not ideal. The information is designed to give maintenance crews an indication of what systems will need to be tested when the plane lands and what tools and parts should be on hand for the task. Such maintenance data is not an alternative to a Flight Data Recorder. There are also problems since the ACARS messages are held in a one minute suspense window and are grouped by item and priority. Certain message evaluation rules are clearly compromises. A fault detected by a system is considered more serious if it relates to a separate system than if it is a self-detected internal fault. A fault is deemed to be hard if it persists for thirty seconds whereas a fault is deemed soft if it is detected for less than thirty seconds. Such rules do make sense in most circumstances.
The loss of satellite uplink carrier signal during a critical time is one argument against replacing physical black boxes with constant electronic transmission of the FDR and CVR data. The cost of such transmissions is a major problem also.
I'm sure it will be an interesting program and I look forward to viewing it. I hope all my many readers (LOL) will enjoy it.
By the way, the most relevant incident to compare AF447 with is the Gimli Glider incident. That plane ran out of fuel half way through its flight and all the design errors, pilot errors and ATC errors were countered by one thing alone, pilot expertise. The pilot had a hobby of flying gliders, so when he suddenly found himself flying a huge ungainly glider full of passengers, he still knew what to do and how to do it. He had flown gliders before. He knew to make his S turns toward his objective and not lose sight of it. He knew how to do skids. He was flying the airplane rather than monitoring computers but everything turned out okay because he was used to actually flying the airplane rather than monitoring computers. That is a rare skill nowadays.
With AF447 when things turned so bad that the computer entered Alternate Law mode the computer would no longer override disapproved pilot inputs and would allow the pilots to fly the aircraft as they saw fit. Unfortunately, the pilots were not very experienced at actually flying the aircraft and were not able to do it in situations of high informational overload, high insecurity as to the reliability of their instruments and unusual attitudes. When Fly-By-Wire ended and Alternate Law started, the situation was already critical and the pilots desperately needed a learning curve. Unfortunately, there is no learning curve during such an event. If you've entered even the fringes of a supercell at night and are experiencing electrical overloads, have circuit breakers popping all over the place, are losing some instruments and have utterly lost faith in all your instruments, the situation is hopeless for a pilot who really doesn't know how to fly an airplane without a computer.
Every flight using a computer to change altitude saves on fuel costs over a heavy handed pilot trying to manipulate the throttles, but every such flight deprives the pilot of real flying experience. Just as the Gimli Glider incident involved a sudden transition the AF447 undoubtedly involved a sudden transition even though we don't know the cause. Initial lightning seems insufficient. Iced-up pitot sensors can have any number of causes. Auto Pilot and Auto Thrust are different systems and some confusion may have existed as to speed selection and the rapidity of speed adjustment attempts that were required.
If there was a deep stall, I just wonder what attitude is required for it. Note: A Deep Stall is one wherein no manipulation of power or control surfaces will have sufficient effect. A pilot in the deep stalled plane is as utterly helpless as a pilot on the ground who might be observing the incident. The pilot on the ground will push a non existent throttle lever, the pilot in the plane will push an actual throttle lever however the effect will be the same. A pilot on the ground will push an imaginary steering yoke, a pilot in the plane will push a real steering yoke yet the results will be the same. No effect whatsoever. A deep stall with or without a flat spin would mean a high speed vertical descent with little forward momentum.
NOTE: On Feb 28 2011, the Alucia arrived, fresh from a Seattle overhaul, at the Pacific waiting area for transiting the Panama Canal to begin its three phase search for the Black Boxes using remote controlled submersibles.
NOTE: This Phase 4 search continues. IF there is a Phase 5, Recovery Phase, a different ship and different equipment will be used. So far, no debris field has been discovered much less the "black boxes". (April 2nd, 2011).
Debris Field found. Learmount of Flight International being quoted on theory of crew fatigue induced fixation on minor problem while plane was in an unnoticed gentle descent resulting in a collision of an intact and controllable plane with the sea. He does not believe there was any deep stall. Merely pilots having lost so many instruments that they did not believe what few instruments remained.
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