B737 Max "fix"
B737 Max "fix"
(OP)
hot off the press (from Flight) ...
one part of the fix concerns/interests me ...
"If those inputs (talking about upgrading the system to compare the two sensors) vary by more than 5.5°, the system will inhibit MCAS and the entire speed trim function for the remainder of the flight," a Boeing official says. "That first level of protection… will keep MCAS from ever firing in the case of a single angle-of-attack" error, he adds
ok, you'll no doubt have some "MCAS INOP" warning. But if you can fly the remainder of the flight without MCAS, why have it in the first place ? How can you be sure not to encounter an MCAS event later in the flight ?? Is "MCAS OP" (as opposed to MCAS INOP) on the MMEL ??
why do we need another stick pusher ? ie we have good systems already protecting the plane before we had MCAS ?
one part of the fix concerns/interests me ...
"If those inputs (talking about upgrading the system to compare the two sensors) vary by more than 5.5°, the system will inhibit MCAS and the entire speed trim function for the remainder of the flight," a Boeing official says. "That first level of protection… will keep MCAS from ever firing in the case of a single angle-of-attack" error, he adds
ok, you'll no doubt have some "MCAS INOP" warning. But if you can fly the remainder of the flight without MCAS, why have it in the first place ? How can you be sure not to encounter an MCAS event later in the flight ?? Is "MCAS OP" (as opposed to MCAS INOP) on the MMEL ??
why do we need another stick pusher ? ie we have good systems already protecting the plane before we had MCAS ?
another day in paradise, or is paradise one day closer ?
RE: B737 Max "fix"
If I am correct, then since I am not privy to the Boeing internal process, I would speculate that Boeing considered the MCAS to be a better solution than attempting to alter the stick pusher function. And more speculation on my part would be that the stick pusher only involves the elevators, and Boeing decided that the stabilizer trim system was required to compensate for this new challenge due to its far greater impact on aircraft pitch under the imposed flight loads. In short, the elevator alone was insufficient to resolve this new challenge.
So the bottom line would be (again, speculation on my part) the "good systems" as you stated that protected the plane prior to the MAX relocation of the engines to accommodate their larger size no longer protected the plane per regulatory requirements, and moving the stabilizer trim with its greater ability to manage pitch attitude versus flight loading was chosen as the fix.
Darn good question though. I wish I had access to more accurate and detailed "insider" information.
RE: B737 Max "fix"
What did change is the size of the engines leading to an increase in the lift the engines produce at high angle of attack.
MCAS was for a regulatory requirement that stick force be linearly proportional to AoA. With the additional lift as AoA increased this requirement was not met in the MAX series, hence the use of stab trim to linearize the force. Note that enlarging the stab would likely not have linearized the response as the engines provide a non-linear input.
If MCAS is not enabled then there is a small increase in the chance that the pilot will fully stall the aircraft if it is operated at low speed with no flaps. Note that MCAS is not enabled when flaps are deployed.
RE: B737 Max "fix"
RE: B737 Max "fix"
I think we're on the same page. I don't think Boeing did a sloppy job certifying the Max. I'm sure a search-light was shone on the MCAS and if anything was amiss it would have been found and discussed. I guess they were caught out be the reliability of the sensor ? Their previous fix was (I think) mostly training, now because of the "fuss" they're doing more (that they don't really need to do, but need to be seen doing).
another day in paradise, or is paradise one day closer ?
RE: B737 Max "fix"
RE: B737 Max "fix"
"The AoA system is MEL, and Lion Air took off with it still defective like it was the day before."
It is obvious from the analysis report that you are entirely correct in the technical sense, in that Lion Air took off with the AoA still defective. However, correct me if I err, but I believe the maintenance team used the required procedures to troubleshoot and clear the logbook entry. So from an airworthiness standpoint, the fault was cleared, although subsequent events prove that the required procedures were insufficient to diagnose and clear the actual fault.
If I am correct, then the accident flight crew took off with the belief that the fault actually had been cleared. Would you agree with this assumption on my part?
RE: B737 Max "fix"
another day in paradise, or is paradise one day closer ?
RE: B737 Max "fix"
According to the flight recorder data images presented, only one AoA sensor was indicating the correct value prior to takeoff.
TTFN (ta ta for now)
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RE: B737 Max "fix"
AFAIK the maint crew did not correctly diagnose the problem and poked at some other area and considered what they did as good. They did nothing to confirm that the system functioned correctly under flying conditions.
This is in part because the previous crew misrepresented the extent of the problem and failed to note that stab trim ran sporadically on its own until they were forced to shut it off.
AFAIK the flying crew had no information about the fault as experienced and were therefore completely unprepared to deal with the problem when it recurred.
RE: B737 Max "fix"
RE: B737 Max "fix"
Supposedly, per the report, "After parking, the PIC informed the engineer about the aircraft problem and entered IAS and ALT Disagree and FEEL DIFF PRESS problem on the AFML." Nothing about flying with a stick shaker for nearly 2 hours. Nothing about shutting off the stab trim. Nothing about the trim fighting them for 10 minutes.