Indonesian aircraft missing off Jakarta
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That would be the logical thing to do. Recognizing that repeated uncommanded trim movements occurring in a regular pattern are indeed "continuous" would be another. Both actions would require logical thinking and what we used to call "flying by the seat of one's pants." Reading this thread it appears these concepts have died in favor of computers and checklists.
Is "it wasn't done because there's no checklist for it" a valid defense strategy? It appears Boeing's "Legal Eagles" are chomping at the bit to test that line in court with a long line of expert witnesses. First in that line will be the surviving Lion Air crew that took the appropriate action on the previous flight(s). The depositions would make compelling reading and something we are unlikely to ever see if the case even gets that far.
Once cockpit control is ceded to the realm of 1's and 0's, pilots become obsolete. Be careful what you wish (advocate) for.
Is "it wasn't done because there's no checklist for it" a valid defense strategy? It appears Boeing's "Legal Eagles" are chomping at the bit to test that line in court with a long line of expert witnesses. First in that line will be the surviving Lion Air crew that took the appropriate action on the previous flight(s). The depositions would make compelling reading and something we are unlikely to ever see if the case even gets that far.
Once cockpit control is ceded to the realm of 1's and 0's, pilots become obsolete. Be careful what you wish (advocate) for.
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IF both crew arepulling on conrol column with maximum force due to artifical feel increase driven by AOA, how does either one have the time or ability to rotate trim wheel 20 to 30 or more revolutions with maybe 30 seconds or less to impact ??
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Mechanical trim wheel use is shown on the trace by change of trim position absent any singal on two top lines. The only case of this I can see is at the very end of the trace.
Last edited by AlexGG; 28th Nov 2018 at 21:27.
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Bottom line is that the aircraft flew with the same faults as the previous flight. The previous flight crew followed procedures properly (followed NNCs, declared a PAN), and safely completed the flight. But they DID NOT make proper entries in the log so the maintenance staff could properly understand the issue. Saying the trim was "running the wrong way" is not the same as "it was constantly trimming nose down with the stick shaker going". Much of Lion Air's subsequent Notices have been regarding making proper log entries.
We really have no idea what was wrong with the air data system on a brand new jet. What we do know is that it wrongly caused some anti-stall protections to activate -- stick-shaker, automatic nose-down trim, heavy elevator feel. One crew managed that properly, another didn't. They didn't even declare a PAN. I don't know how anyone can suggest that constant or repeated nose-down automatic trim wouldn't lead a crew to follow the runaway stabiliser checklist.
We really have no idea what was wrong with the air data system on a brand new jet. What we do know is that it wrongly caused some anti-stall protections to activate -- stick-shaker, automatic nose-down trim, heavy elevator feel. One crew managed that properly, another didn't. They didn't even declare a PAN. I don't know how anyone can suggest that constant or repeated nose-down automatic trim wouldn't lead a crew to follow the runaway stabiliser checklist.
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I just got a chance to read the whole report. The crew on the flight prior to the accident ran the "Runaway Stabilizer" checklist. Apparently Boeing needs to rewrite this checklist to include "Plan to land at nearest suitable airport" at the end. 
We're told in a previous post that a single revolution of the trim wheel only moves the stab up or down by one-tenth of a degree (though I've seen another source that suggests it's even less than that).
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And did the Runaway Stabilizer NNC have the caution that MCAS has been lost?
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Good Question
I've been watching this thread carefully, from the day of the crash. Since we all learned of the existence of MCAS, I've been wondering when this and jimtx's earlier question would arise. What, exactly, happens to longitudinal stability of the MAX in the absence of MCAS?
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I've been watching this thread carefully, from the day of the crash. Since we all learned of the existence of MCAS, I've been wondering when this and jimtx's earlier question would arise. What, exactly, happens to longitudinal stability of the MAX in the absence of MCAS?
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Right. But the reason MCAS was implemented on the MAX is that the aircraft has a tendency to pitch up in conditions where that would not be the case with earlier 737 versions, correct?
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MCAS appears designed to give assistance to using the elevator to recover from a high AoA condition. Likely the scenario for which it is implemented also includes some combination of high thrust (causes nose-up moment) and stab trimmed to abnormally nose-up position. Both 737NG and, I think, at least one AB variant have had high pitch angle upsets in very similar conditions, and the concern for such a scenario has been the subject of more general discussions. Thus Boeing, perhaps prodded by FAA, seem to have implemented a "helper" to trim the stab a bit nose-down for such a case. While the MAX has more thrust than NG and thus more nose-up possibly in the scenario I don't think it's a black-and-white "problem on MAX not on NG" - I suspect it's shades of grey.
The MAX has larger engine casings that are mounted further forward than earlier 737's. At high AoA's, those engine casings start generating lift, which creates a nose up pitching moment. The MCAS is designed to counteract this by creating an opposite nose down pitching moment through the stabiliser.
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The MAX has larger engine casings that are mounted further forward than earlier 737's. At high AoA's, those engine casings start generating lift, which creates a nose up pitching moment. The MCAS is designed to counteract this by creating an opposite nose down pitching moment through the stabiliser.
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From the peanut gallery, sort-of, not totally 100%.
MCAS appears designed to give assistance to using the elevator to recover from a high AoA condition. Likely the scenario for which it is implemented also includes some combination of high thrust (causes nose-up moment) and stab trimmed to abnormally nose-up position. Both 737NG and, I think, at least one AB variant have had high pitch angle upsets in very similar conditions, and the concern for such a scenario has been the subject of more general discussions. Thus Boeing, perhaps prodded by FAA, seem to have implemented a "helper" to trim the stab a bit nose-down for such a case. While the MAX has more thrust than NG and thus more nose-up possibly in the scenario I don't think it's a black-and-white "problem on MAX not on NG" - I suspect it's shades of grey.
MCAS appears designed to give assistance to using the elevator to recover from a high AoA condition. Likely the scenario for which it is implemented also includes some combination of high thrust (causes nose-up moment) and stab trimmed to abnormally nose-up position. Both 737NG and, I think, at least one AB variant have had high pitch angle upsets in very similar conditions, and the concern for such a scenario has been the subject of more general discussions. Thus Boeing, perhaps prodded by FAA, seem to have implemented a "helper" to trim the stab a bit nose-down for such a case. While the MAX has more thrust than NG and thus more nose-up possibly in the scenario I don't think it's a black-and-white "problem on MAX not on NG" - I suspect it's shades of grey.
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Crew appeared in control
The pilots on lion 610 were in regular contact with ATC and as late as 20 seconds before impact with the ocean they indicated their preferred flight level. This suggests they were not under duress in operating the aircraft until the very end. It is still very much unclear why their successful and consistent NU trim corrections are suddenly insufficient to counteract MCAS.
Aviation Herald has posed these questions to the FAA who declined to answer them while the investigation was ongoing. The last two questions were missed:
"With respect to the certification of the 737 MAX aircraft, in particular the MCAS system, I'd like to raise following questions:
- when was the certificate for the 737 MAX 8 requested, and when was the certification issued?
- what risk assessments were done within the certification procedures, in particular again with respect to the AoAs and MCAS?
- were the ADR (Air Data Reference) algorithms reviewed with respect to AoA?
- was the risk assessed that one of the AoA sensors could be damaged by a bird strike, hail strike or similiar and could show a substantially too high angle of attack?
- did the certification deem not necessary that an "AoA Disagree" message was to be introduced?
- Why was the MCAS permitted to operate on the base of a single AoA value showing too high angle of attacks? Why does the MCAS not consider the other AoA value?
- Was the risk assessed according to Boeing's last sentence in the notice to operators: "If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.", in particular what possibilities existed for that conditions to persist?
- what should the system response have been in case the AoA values disagree? How would the systems determine which value is plausible and which is erroneous? Is there any such check at all? Would MCAS not need to be prohibited if left and right AoA disagree?
- considering the scenario that happened to Airbus twice (the crash in Perignan and the Lufthansa A321 near Bilbao losing 4000 feet), that at least two AoA sensors froze in same positions during climb, was the risk of such a scenario on the 737s assessed, too?
- Did the certification consider a massive change in the function of the AoA when MCAS (as actor in the flight controls) was introduced in addition to stick shaker (monitoring only)?
- What is the reasoning behind the certification permitting to allow a system modify the aircraft's equilibrium (via trim) in manual flight in a way that the trim could run to the mechanical stop and thus overpower the elevator?
- Was the AoA input to the MCAS (or in general) ever being cross checked, e.g. by taking into account altitude, IAS, vertical speed to compute TAS via altitude, density and IAS and the angle of the airflow by computing the angle of the flight trajectory with TAS and vertical speed? Could such an crosschecking algorithm not even detect if two or more AoA sensors were frozen/faulty?
- is the FAA going to review the certification of the 737 MAX family (and perhaps previous 737 versions) following the findings by the KNKT so far?
- Russia's MAK revoked the certificate of airworthiness for the entire 737 family (from 737-100 to 737-900) three years ago claiming they found an issue in the pitch/altitude control system of the aircraft (suggesting that at least the Tatarstan crash in Kazan as well as the Flydubai crash in Rostov may have been the result of that weakness) but did not receive a satisfactory response by the FAA and Boeing, also see News: Russia suspends airworthiness certification for Boeing 737s, but does not prohibit operation of 737s. What was the issue they found?
The questions we forgot to add:
- How the certification deal with spurious faults and spurious functions, in particular during maintenance? The maintenance manuals define a test to be run, then list maintenance steps one by one, the test is to be repeated after each step. If the system is found to be working during the test the maintenance task aborts with the message "You have solved the issue", which may trigger a wrong analysis and premature end of troubleshooting without removing the fault if the test apparently works correctly by random chance.
- Why do the FIM procedures for airspeed disagree, altitude disagree, feel difference light, inexplicable stick shaker activation etc. not reference the possibility of an AoA issue although AoA has a crucial influence onto all these error conditions, thus not guiding the AME to verify proper action of this input in each of these error conditions?"
"With respect to the certification of the 737 MAX aircraft, in particular the MCAS system, I'd like to raise following questions:
- when was the certificate for the 737 MAX 8 requested, and when was the certification issued?
- what risk assessments were done within the certification procedures, in particular again with respect to the AoAs and MCAS?
- were the ADR (Air Data Reference) algorithms reviewed with respect to AoA?
- was the risk assessed that one of the AoA sensors could be damaged by a bird strike, hail strike or similiar and could show a substantially too high angle of attack?
- did the certification deem not necessary that an "AoA Disagree" message was to be introduced?
- Why was the MCAS permitted to operate on the base of a single AoA value showing too high angle of attacks? Why does the MCAS not consider the other AoA value?
- Was the risk assessed according to Boeing's last sentence in the notice to operators: "If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.", in particular what possibilities existed for that conditions to persist?
- what should the system response have been in case the AoA values disagree? How would the systems determine which value is plausible and which is erroneous? Is there any such check at all? Would MCAS not need to be prohibited if left and right AoA disagree?
- considering the scenario that happened to Airbus twice (the crash in Perignan and the Lufthansa A321 near Bilbao losing 4000 feet), that at least two AoA sensors froze in same positions during climb, was the risk of such a scenario on the 737s assessed, too?
- Did the certification consider a massive change in the function of the AoA when MCAS (as actor in the flight controls) was introduced in addition to stick shaker (monitoring only)?
- What is the reasoning behind the certification permitting to allow a system modify the aircraft's equilibrium (via trim) in manual flight in a way that the trim could run to the mechanical stop and thus overpower the elevator?
- Was the AoA input to the MCAS (or in general) ever being cross checked, e.g. by taking into account altitude, IAS, vertical speed to compute TAS via altitude, density and IAS and the angle of the airflow by computing the angle of the flight trajectory with TAS and vertical speed? Could such an crosschecking algorithm not even detect if two or more AoA sensors were frozen/faulty?
- is the FAA going to review the certification of the 737 MAX family (and perhaps previous 737 versions) following the findings by the KNKT so far?
- Russia's MAK revoked the certificate of airworthiness for the entire 737 family (from 737-100 to 737-900) three years ago claiming they found an issue in the pitch/altitude control system of the aircraft (suggesting that at least the Tatarstan crash in Kazan as well as the Flydubai crash in Rostov may have been the result of that weakness) but did not receive a satisfactory response by the FAA and Boeing, also see News: Russia suspends airworthiness certification for Boeing 737s, but does not prohibit operation of 737s. What was the issue they found?
The questions we forgot to add:
- How the certification deal with spurious faults and spurious functions, in particular during maintenance? The maintenance manuals define a test to be run, then list maintenance steps one by one, the test is to be repeated after each step. If the system is found to be working during the test the maintenance task aborts with the message "You have solved the issue", which may trigger a wrong analysis and premature end of troubleshooting without removing the fault if the test apparently works correctly by random chance.
- Why do the FIM procedures for airspeed disagree, altitude disagree, feel difference light, inexplicable stick shaker activation etc. not reference the possibility of an AoA issue although AoA has a crucial influence onto all these error conditions, thus not guiding the AME to verify proper action of this input in each of these error conditions?"
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Can someone please explain to me how to following can be possible:
The actual trim position increases without any manual or automatic trim increase (in the upward direction) with the CUT OUT in operation. The only automatic and manual inputs are down, but the trim position moves up. Or am I reading everything backwards?
The actual trim position increases without any manual or automatic trim increase (in the upward direction) with the CUT OUT in operation. The only automatic and manual inputs are down, but the trim position moves up. Or am I reading everything backwards?
Edit: Yes, manual trimming with the trim wheel only shows up as trim position, not as trim input. So at the end of the previous flight, they were spinning the big wheel around by hand.
S
Last edited by silverstrata; 29th Nov 2018 at 08:43.
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The MAX has larger engine casings that are mounted further forward than earlier 737's. At high AoA's, those engine casings start generating lift, which creates a nose up pitching moment. The MCAS is designed to counteract this by creating an opposite nose down pitching moment through the stabiliser.
S
While a few of those questions are ones that have been asked, quite reasonably, in these columns, others are naive (is the FAA going to review certification?), irrelevant (sensor icing???) or easily answered from public sources (when was the Max 8 certificated? [March 8, 2017, Simon]).