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Originally Posted by gums
(Post 10425894)
Salute!
----------------------------------------- I am trying to follow the ROE for our forum, but it's getting hard. I do not mean to diminish the length and breadth of experience that many pilots here have contributed to the discussion. But somethimes I get a little testy. My fear is that some lurking here will think that we lost two planes and 300 passengers because incompetent crews did not simply turn off two switches within seconds of raising flaps at normal altitude and speed with the stall warning system telling them they were stalling and their airspeed was FUBAR. The primary contributing factor to loss of control in the Lion crash and likely the Ethiopian one ,is gonna be the MCAS and its implementatio without fairly documenting it for the crews and not considering its activation at a corner of the envelope it was not intended for. Gums... |
Current comment from Mr G Thomas quoting Greg Feith :
“However, the disturbing reality is that it took a pilot who was not in command of the flight, and just an observer, to tell the captain and first officer (who were supposedly trained, qualified, and experienced in the operation of the Boeing 737 MAX) what the issue was that resulted in the nose of the airplane pitching down (uncommanded pitch trim input also known as a “runaway trim”),” he said. “The fact that the pilots who were in command of the flight and had access to the flight controls did not recognise nor properly respond to the “runaway trim” event is a testament of a more systemic problem within Lion Air.” There are four failures that will cause a runaway trim on a standard 737 and five on a MAX version with the new background software to help the pilots fly the plane.It was not this software that caused the crashes, rather faulty sensors feeding it incorrect data. “ The flight crews’ failure to understand the issue and implement the proper corrective actions (which are memory items) is a symptom of a more serious problem and a likely explanation for the loss of the airplane if the accident crew reacted in the same manner – confused, panicked and hoping to find the answer in book rather than reverting to what they would have learned in training,” Mr Feith said. On the Ethiopian crash, Mr Feith said that it was “also of interest that it took the Ethiopian investigative team five days to find a place to have the FDR and CVR data downloaded and converted to a medium that could be used by investigators to determine the initiating event that led the pilots to lose control of the airplane.” |
Originally Posted by TriStar_drvr
(Post 10426007)
No. At rotation flaps would be extended. MCAS does not engage with the flaps extended.
How the heck they ever got this through part 14cfr chapter 25 certification reliant on only 1 sensor? Seems to me, in the rush to fix one certification issue, someone forgot the rest. Ttfn |
I have flown with AoA indicators on various corporate jets.
I found them extremely useful as a conformation for approach and departure speeds. Why they are not standard on larger jets is puzzling. If MCAS was a bodge, how many other bodges were found acceptable |
Originally Posted by PaxBritannica
(Post 10426233)
I can't see that a quick fix for MCAS is going to reassure the travelling public, ie me. If MCAS was a bodge, how many other bodges were found acceptable? If this was the only place in the design where engineers were asked to take a 'small' risk, I suspect whispers would have gotten around long before the plane flew. Therefore, it's likely that it was just one of many other design 'solutions' where the idea of tolerable risk was normalised.
No software patch will fix systemic management hubris. |
Originally Posted by gums
(Post 10425894)
Salute!
---snip--- I am trying to follow the ROE for our forum, but it's getting hard. I do not mean to diminish the length and breadth of experience that many pilots here have contributed to the discussion. But somethimes I get a little testy. My fear is that some lurking here will think that we lost two planes and 300 passengers because incompetent crews did not simply turn off two switches within seconds of raising flaps at normal altitude and speed with the stall warning system telling them they were stalling and their airspeed was FUBAR. The primary contributing factor to loss of control in the Lion crash and likely the Ethiopian one ,is gonna be the MCAS and its implementatio without fairly documenting it for the crews and not considering its activation at a corner of the envelope it was not intended for. Gums... Mostly everyone here who is *not* a pilot realizes that the rushed certification of the Max is the real issue. AFAIK nobody except Boeing lawyers and maybe the families is going to lay the blame on those pilots. Anyone, pilot or not, who reads the details of MCAS spooling up time and again in those cockpits thinks "there but for the grace of God go I". But there is one interesting question though which is why those who survived such MCAS incidents prior to the Lion Air crash did not document them and raise a stink. Was it because they thought they had made an operational mistake? Edmund |
QF72 - A330
Running through TiVo tonight I came across the Air Disaster documentary on QF72. It's an A330 but at a high-level there is a lot in common with these recent tragedies.
https://www.smithsonianchannel.com/s...ll/802/3467449 |
I can’t see any foreign regulatory authority allowing the Max into its airspace without an extensive modification of the stall avoidance system and an in-depth training program for Pilots and engineers. A separate type rating covering the Max, rather than relying on a current B737 rating is a real possibility. A new type certificate might also be on the cards as well. After two disasters, no authority is going to sign off on a solution unless it’s iron clad and well in excess of what’s required, a software update isn’t going to be enough. No pilot will be flying a Max until he’s demonstrated proficiency in dealing with any possible MCAS failures a simulator. |
Originally Posted by BobM2
(Post 10426270)
It is amazing the amount of Boeing bashing on this forum. Boeing has made tens of thousands of safe & efficient airliners for more than half a century & that's why there are more Boeings than anything else. Every airplane design is a compromise that needs to be tweaked in one way or another to meet certification requirements. This process takes many months & involves much actual test flying. The much maligned MCAS was a tweak to meet an obscure certification requirement that was probably never going to be encountered in the life of the airplane. A lot of effort over decades has gone into making the aircraft as safe & foolproof in operation as possible. But, how do you design for an airline that flies an aircraft for three days with unreliable airspeed, maintenance that then compounds the problem with a bad AOA installation, & flight crews that still try to complete the flight with a continuous stick shaker? We don't know yet about Ethiopian, but if it was the same malfunction after all the warnings & publicity worldwide from Lion Air, then that is the height of incompetence.
I've a rare option Ford Focus Ghia without ABS brakes, which i hate (ABS that is)... When I maybe have to buy one with ABS I'd hope the Driver's Handbook actually mentioned the fact ! |
Originally Posted by Alchad
(Post 10426175)
It seems to be accepted that there are such similarities between the Indonesian and the Ethiopian crashes that – I suspect – a lot of people are assuming the cause of the accidents will also be similar. However, one difference between the two crashes which doesn’t appear to have aroused all that much speculation, at least as far as I can determine, is the fact that the Ethiopian 737 only managed to get to perhaps 1000 feet (according to Flightradar24), whereas the Indonesian 737 appeared to achieve 5000 feet and the pilots consciously settled for that altitude. This is where my non- aircraft background becomes apparent and the reason for my question; which is basically what caused ET 302 to be unable to get above 1000 feet? Minimum flap retraction altitude for B737 is 400 ft so possible MCAS-activation at low altitude. Also there seems to be an assumption that the MCAS would bug them continuously after that unless they switched trim off. In the LionAir crash prel report a difference of 20 deg throughout the flight and stick shaker active for most of the rest of the flight. I e there seems to be a systematic error in one of the AoA sensors that would only activate shaker when they flew with an actual AoA above a certain level. Same would then hold true for MCAS-activation. With just the "right" systematic error in one of the AoA-sensors ET302 could have been perfectly trimmable flying at constant altitude with AoA below the threshold. As soon as they tried to ascend increasing true AoA to proper MCAS-activation angle minus systematic offset they would have been "pushed down" but could have trimmed out again. So they are in a "perfectly good airplane" as long as they zoom along at breakneck speeds at a constant altitude above sea level. If ground level (above sea level) increases they would be destined to meet with terra firma sooner or later...unless they used the elevator...and got hammered by MCAS again. And for the complaints about their speeding: Thrust reduction? No go. You'd sink unless you increased AoA above the threshold...and got hammered again.´´´´´´´ |
Originally Posted by edmundronald
(Post 10426273)
Gums,
But there is one interesting question though which is why those who survived such MCAS incidents prior to the Lion Air crash did not document them and raise a stink. Was it because they thought they had made an operational mistake? Edmund |
Originally Posted by PaxBritannica
(Post 10426233)
I can't see that a quick fix for MCAS is going to reassure the travelling public, ie me. If MCAS was a bodge, how many other bodges were found acceptable? If this was the only place in the design where engineers were asked to take a 'small' risk, I suspect whispers would have gotten around long before the plane flew. Therefore, it's likely that it was just one of many other design 'solutions' where the idea of tolerable risk was normalised.
No software patch will fix systemic management hubris. |
Originally Posted by HarryMann
(Post 10426289)
Yes, though that Bob is why you as a manufacturer should Tell them what the heck you've done to the stab trim circuit... which it sounds ominously like was poorly or undocumented. Nor we are told, was much if anything made of it as a 'difference' feature in any training (?).
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Originally Posted by Kerosene
(Post 10424795)
Suppose MCAS becomes unavailable during flight e.g. due to Stab trim deactivation. The MAX’s flight characteristics in approach to stall scenarios proved not certifiable without MCAS as a fix. I’d like to ask the ones in the know (FcEng and others) how critical the loss of MCAS in flight would be in real life. For example, encountering a flight upset with approach to stall, how easily can this be recovered without MCAS? How was the risk of such an event assessed? Was it demonstrated in test flights? Why was it determined there would be no need to train flight crews on the simulator for the changed handling outside the certification parameters? In a previous post I assumed such a scenario to be critcal, but perhaps it isn’t? Thanking you in advance for shedding light on this issue. Is there any recorded valid activation of MCAS? Is it even possible that we have a tick box implementation for certification purposes that has achieved nothing other than promote accidents? |
But, how do you design for an airline that flies an aircraft for three days with unreliable airspeed, maintenance that then compounds the problem with a bad AOA installation, & flight crews that still try to complete the flight with a continuous stick shaker? We don't know yet about Ethiopian, but if it was the same malfunction after all the warnings & publicity worldwide from Lion Air, then that is the height of incompetence. Life isnt black and white like that. Its not all Boeings fault.Its not all the pilots fault for not cutting out those 2 switches. I think it was mentioned by FCENG84 that designers design safe in the knowledge that airline pilots have a minimum standard of airmanship and that line engineers know their job and follow the MEL.Lionair's reputation is not a good one. And frankly speaking,neither is Ethiopian.So its a difficult.situation to analyse.Do I think either accident could have happened in Southwest?No,I do not. Boeing obviously considered the consequences of a faulty sensor and its effect on MCAS prior certification.They knew this would occur at flap retraction at low altitude and would result in stick shaker,unreliable airspeed and considerable and unexpected nose down trim all at once.They decided that this failure scenario was one step shy of "catastrophic". and that a crew would cope.Maybe they under-rated the effect of the stick shaker on the pilots ability to react in the correct manner.Those shakers can scramble your brain and degrade reaction time and pilot response.They can cause startle factor which I know is sometimes derided as an excuse for poor airmanship.But it can happen and it can affect quite a few crews. Whats not okay is if they deliberately downgraded it below "catastrophic" to rush certification and avoid further analysis and fine-tuning of the design.If they genuinely miscalculated the effect of unwanted MCAS at low altitude and so designed it to work off one sensor only,then its just an error. However,if they downgraded it below "catastrophic" to rush certification then it was a cynical decision and thats negligence. |
Originally Posted by Rananim
(Post 10426330)
Boeing obviously considered the consequences of a faulty
sensor and its effect on MCAS prior certification.They knew this would occur at flap retraction at low altitude and would result in stick shaker,unreliable airspeed and considerable and unexpected nose down trim all at once. |
Originally Posted by Rananim
(Post 10426330)
Boeing obviously considered the consequences of a faulty sensor and its effect on MCAS prior certification.They knew this would occur at flap retraction at low altitude and would result in stick shaker,unreliable airspeed and considerable and unexpected nose down trim all at once. |
SLF here, but with a background in experimental physics dealing with personnel and equipment safety in large-scale, hazardous experimental situations.
Assuming that both 737 MAX crashes were the result (in large part) of faulty AOA probe data, then we already know, from sad experimental evidence, that relying on one probe is unacceptable. With 2 hull losses in N (? - not a terribly large number) flights of this aircraft, the reliability statistics are hardly at the flight-safety-critical level. Having an "AOA disagree" warning or AOA readouts for pilots is not necessarily going to help. I suggest that as a minimum, with only two AOA probes (and that should be the minimum number), that MCAS should shut itself down in an AOA disagree situation (with notification to the pilots). The principle here is "primum non nocere". The aircraft is not going to have an upset just because MCAS is not there on these rare occasions. Furthermore, if AOA data is going to be used in this way (possibly killing people if it is wrong), further sanity checks should be applied to the probe data (e.g., AOA pre-rotation on take-off, consistency with inertial and other air data, whatever). MCAS as currently implemented seems like a horrid kluge to a non-pilot, but I'm inclined to believe, from what I've read here, that with better engineering (and not too drastic a change) the 737 MAX could be restored to safe service. |
Rananim, a faulty AOA that would activate MCAS would produce a continuous stick shaker at rotation, not on flap retract. Why would any right-thinking pilot ever attempt to retract flaps & continue the flight with an active stick shaker, even if unaware that MCAS exists? Yes you are of course correct but that doesnt alter the fact that crews who elect to retract flaps and climb to MSA as per SOP would face all 3 concurrently with flaps up.You assert that no crew would retract flaps and climb to MSA to perform checklists and I hope you are right.I agree with not retracting flaps and just landing from circuit height but I dont assume thats what all crews would do,especially if unfamiliar with MCAS. |
Originally Posted by Rananim
(Post 10426347)
BobM2
Yes you are of course correct but that doesnt alter the fact that crews who elect to retract flaps and climb to MSA as per SOP would face all 3 concurrently with flaps up.You assert that no crew would retract flaps and climb to MSA to perform checklists and I hope you are right.I agree with not retracting flaps and just landing from circuit height but I dont assume thats what all crews would do,especially if unfamiliar with MCAS. |
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