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The Boeing 737 Technical Site
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Originally Posted by FCeng84
(Post 10419944)
Good idea to pull aside and have a level setting. I concur with everything added to the thread so far. Let me point to one possible source for the confusion about the role of ALTitude in the activation of MCAS. I recall that in the ET accident thread at one point there were several submissions wondering if MCAS could have played a role based on the data suggesting that the airplane did not gain much ALTitude and thus speculating that the flaps would have still been extended. I believe that at least one entry suggested that on climbing out of Addis Ababa it would not be abnormal to be cleaned up to flaps up by the point where the airplane was 1000' above the runway ALTitude. This may have been seen by some as indication that MCAS has logic to prevent activation below 1000'. I am not aware of any direct use of ALTitude in the activation of MCAS. I am checking with a source and will report back once this is confirmed or denied.
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Salute FCeng !
Great to have most of our understnding confirmed. Assume the "few feet of the ground" criteria might even be ground effect that influences AoA/downwash, or #2 radar altimiter. @JT PLZ let this one stay! Several of the inputs here by Dave, CONSO and Gums were deleted and they included real world examples that the lay person could visualize concerning AoA, as well the fallacy of using pendulums or plumbobs as AoA or other indicators. Many on the main threads are still confusing attitide they reference to siting in a living room chair with aerodynamic pitch and AoA and ..... Gums sends... |
Originally Posted by Ian W
(Post 10422394)
I am surprised that after the Lion Air crash and the AD that any pilot on the Max would be unaware of the MCAS issue and have briefed accordingly before any flight about stab trim cutout if trimming became difficult - it is part of the standard runaway trip checklist. The fact that another crew had crashed and could have survived if they had switched stab trim to cutout should have concentrated minds.
According to the report the crew that survived MCAS ran 3 NNCs - IAS disagree, ALT disagree, and then Stab Trim Runaway. From the FDR traces they had around four minutes of fighting MCAS, after flaps up, before they turned it off. Ethiopian was in the ground after six minutes of flight. |
Originally Posted by Ian W
(Post 10422394)
I would have thought that the first check on unreliable airspeed in the Max would be set stab trim switches to CUTOUT that means manual trim but MCAS is now out of the loop.
The MCAS was created solely because the B737MAX is sufficiently unstable without it (under some circumstances) to not be certifiable, and the stab trim switches are required to be on for MCAS to work. Boeing have their "gentleman's parts" in a vice on this one |
Originally Posted by infrequentflyer789
(Post 10422821)
ATC comms from both accident flights, and reports from the flight that survived, indicate that the unreliable airspeed was the first focus
From AvHerald: "..., that there had been no PAN PAN or MAYDAY call, there was also no change in transponder code away from the assigned code 2000, there had been no indication of unreliable airspeed by the flight crew, there had been no distress in the voices or abnormal background noises during transmissions from the aircraft that would have alerted air traffic control to assume a serious problem on board of the aircraft." |
Originally Posted by kiwi grey
(Post 10423222)
But that would put the aircraft into a known unsafe condition.
The MCAS was created solely because the B737MAX is sufficiently unstable without it (under some circumstances) to not be certifiable, and the stab trim switches are required to be on for MCAS to work. Boeing have their "gentleman's parts" in a vice on this one |
Right on, whether it's communication breakdown or crew members not knowing where to look up important data.
I wouldn't discount the pressure for on time performance from the airlines and flight crews racing to get to the plane from a previous flight and getting into a hurry up situation. |
Back to the original question : Altitude versus Attitude.
It does not matter; when sensors:systems feed wrong information, the outcome is predictable. About the pilots and pressure on them; Most pilots are trained using the autopilot and protection systems. But => Most are "scared as hell" to turn protection systems OFF. |
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