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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

Old 3rd Apr 2019, 07:08
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Originally Posted by Derfred
There has been very little discussion here on the subject of false stick shaker on rotation.

Lion Air had it on two flights. That we know.

Whilst we don’t yet know anything about Ethiopian, the initial flight profile looks to me like a pilot reaction to a false stick shaker - very slow/erratic climb and rapidly increasing airspeed. Assuming they took off with flaps extended, MCAS would not have contributed to the early part of this profile. The rapidly increasing airspeed may have led them to pull flaps up during the confusion, which may have then led to an MCAS activation.

Identifying false stick shaker on rotation has not formed part of any simulator training I have experienced.
I think that is an excellent description of the sequence of events, and the interaction between the computer and the crew in both events. AFAIK most checklists are not aimed at instantaneous diagnosis of the underlying fault, but rather a patchwork of responses to different flight control situations.

IMO false stick shaker activation (in isolation) is a hazardous condition, because of the additional stress imposed on the crew during a high workload situation. The fact that it cannot be turned off, means it is an ongoing source of distraction, which then becomes a factor for subsequent events.

I would speculate that false MCAS activation on its own (in the absence of any distractions) could have been a more survivable situation, because the crew could focus all their attention on that one single failure. The reality may be that they were already in a 'tunnel vision' hazard evaluation mode, and the MCAS activation was too insidious to be immediately recognised. The 3rd pilot in the earlier Lion Air flight was able to be more objective, outside this process.

I cannot think of any other scenario where false stick shaker activation would present an immediate hazard, which might be why it has not been a training issue. The situation with AF447 was the opposite kind of fault, where the aural stall warning (not stick shaker) was valid but only intermittently active (due to software inhibition), which led to additional confusion.

Edit: My post was drafted before the WSJ article was posted.
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Old 3rd Apr 2019, 07:31
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Originally Posted by fgrieu
So according to the WSJ (paywalled, but regurgitated by Reuters) the pilots of ET302 applied the 2018-23-51 EAD to some degree, flipped the trim switches off, could not correct the nose down condition (or is it move the trim wheel nose up), then flipped the trim switches back on (contrary to the EAD), to no avail.

I ask (because I don't know):
- How hard it is to manually trim nose up, depending on airspeed, current elevator position, AoA..? I have read about an elevator blowback issue, but do not know the details.
- If standard simulator training prepares to that procedure, complete with simulation of how hard it is to turn the wheel. This is critical: If pilots are not well trained to trim up by manual action on the wheel, then mandating them to make it the only way to trim up was nonsense.
>230 knots seem to be an issue according to this article in the Sydney Morning Herald: Regulators knew before crashes 737 MAX trim control could be confusing

Regulators knew before crashes 737 MAX trim control could be confusing

1 April 2019
Singapore: US and European regulators knew at least two years before a Lion Air crash that the usual method for controlling the Boeing 737 MAX's nose angle might not work in conditions similar to those in two recent disasters, a document shows.

The European Aviation and Space Agency (EASA) certified the plane as safe in part because it said additional procedures and training would "clearly explain" to pilots the "unusual" situations in which they would need to manipulate a rarely-used manual wheel to control, or "trim", the plane's angle.

Those situations, however, were not listed in the flight manual, according to a copy from American Airlines seen by Reuters.The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said.
It specifically noted that at speeds greater than 230 knots (425 km/h) with flaps retracted, pilots might have to use the wheel in the cockpit's centre console rather than an electric thumb switch on the control yoke.


EASA and the US Federal Aviation Administration (FAA) ultimately determined that set-up was safe enough for the plane to be certified, with the European agency citing training plans and the relative rarity of conditions requiring the trim wheel.


In the deadly Lion Air crash in October, the pilots lost control after initially countering the Maneuvering Characteristics Augmentation System (MCAS), a new automated anti-stall feature that was pushing the nose down based on data from a faulty sensor, according to a preliminary report from Indonesian investigators released in November.

The flight conditions were similar to those described in the EASA document, a source at Lion Air said. The source said that training materials before the crash did not say the wheel could be required under those conditions but that Boeing advised the airline about it after the crash.

Boeing declined to comment on the EASA document or its advice to Lion Air, citing the investigation into the crash.

Ethiopia's Transport Ministry, France's BEA air accident authority and the FAA have all pointed to similarities between the Lion Air crash and an Ethiopian Airlines disaster last month. But safety officials stress that the Ethiopian investigation is at an early stage.'

Not physically easy'


The crashes have also heightened scrutiny of the certification and pilot training for the latest model of Boeing's best-selling workhorse narrow-body, now grounded globally.

In the EASA document, the regulator said simulations showed the electric thumb switches could not keep the 737 MAX properly trimmed under certain conditions, including those of the Lion Air and Ethiopian Airlines crashes, according to the Indonesian preliminary report and a source with knowledge of the Ethiopian air traffic control recordings.

The trim system adjusts the angle of the nose. If the nose is too far up, the jet risks entering a stall.

Additional procedures and training needed to "clearly explain" when the manual wheel might be needed, according to the document. The EASA spokesman said that was a reference to the Boeing flight crew operations manual.

An American Airlines Group Inc flight manual for 737 MAX pilots dated October 2017 said the thumb switches had less ability to move the nose than the manual wheel.

The manual, which is 1400 pages long, did not specify the flight conditions in which the wheel might be needed.

The trim wheel is a relic of the Boeing 737's 1960s origins and does not appear in more modern planes such as the 787 and Airbus SE A350. It is not often used, several current and former 737 pilots told Reuters.

"It would be very unusual to use the trim wheel in flight. I have only used manual trim once in the simulator," said a 737 pilot. "It is not physically easy to make large trim changes to correct, say, an MCAS input. You - or more than likely the other pilot - have to flip out a little handle and wind, much like a boat winch."

The EASA document said that after flight testing, the FAA's Transport Airplane Directorate, which oversees design approvals and modifications, was concerned about whether the 737 MAX system complied with regulations because the thumb switches could not control trim on their own in all conditions.

FAA declined to comment on the European document. A trim-related "equivalent level of safety" (ELOS) memorandum listed in its 737 MAX certification document is not available on the FAA website. The agency declined to provide it to Reuters.

Confusing signals

The night before the Lion Air crash, different pilots on the same plane faced a similar problem with MCAS and tried to use electric trim to counteract it, according to the preliminary report from Indonesian investigators.

After the third time MCAS forced the nose down, the first officer commented that the control column was "too heavy to hold back" to counter the automated movements, the preliminary report said.

Former FAA accident investigator Mike Daniel said that to prevent stalls, the control column was designed to require more force for a pilot to pull back than to push forward.

Boeing on Wednesday said software changes to MCAS would provide additional layers of protection, including making it impossible for the system to keep the flight crew from counteracting it.

On the 737 MAX, Boeing removed the "yoke jerk" function that enabled pilots to disable the automated trim system with a hard pull on the control column rather than hitting two cut-out switches on the centre console.

In a blog post on his personal website, former Boeing engineer Peter Lemme said that could make things harder for a pilot in a crisis.

"In the scenario where the stabiliser is running away nose down, the pilot may only fixate on pulling the column back in response," he said. "They may not be mentally capable to trim back or cut out the trim - instead they just keep pulling."

Ultimately, the crew the evening before the Lion Air crash stopped the automated nose-down movement with the cut-out switches and used the wheel to control trim for the remainder of the flight, the preliminary report said.

That was the proper procedure to deal with a runaway stabiliser, according to Boeing.

However, current and former pilots told Reuters that the way the trim wheel and other controls behaved in practice compared with in training may have confused the Lion Air crews, who were also dealing with warnings about unreliable airspeed and altitude.

"MCAS activation produces conditions similar to a runaway trim, but the training is not done with a stick shaker active and multiple other failures, which make the diagnosis much more difficult," said John Cox, an aviation safety consultant and former commercial pilot. The stick shaker alerts pilots to a potential stall by vibrating the control column.

Reuters this month reported that an off-duty pilot in the cockpit on the night before the Lion Air crash spotted the runaway stabiliser problem, according to two sources familiar with the matter.

Boeing on Wednesday said changes to the MCAS software would help "reduce the crew's workload in non-normal flight situations".
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Old 3rd Apr 2019, 07:46
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Originally Posted by fgrieu
So according to the WSJ (paywalled, but regurgitated by Reuters) the pilots of ET302 applied the 2018-23-51 EAD to some degree, flipped the trim switches off, could not correct the nose down condition (or is it move the trim wheel nose up), then flipped the trim switches back on (contrary to the EAD), to no avail.

I ask (because I don't know):
- How hard it is to manually trim nose up, depending on airspeed, current elevator position, AoA..? I have read about an elevator blowback issue, but do not know the details.
- If standard simulator training prepares to that procedure, complete with simulation of how hard it is to turn the wheel. This is critical: If pilots are not well trained to trim up by manual action on the wheel, then mandating them to make it the only way to trim up was nonsense.
IMO the critical factor in both crashes (and the difference from the previous Lion Air flights), may have been that the pilots (unintentionally) allowed the speed to rise excessively before trying to intervene with the cutoff switches. Since the auto-throttles were still engaged (they are not disabled by AOA errors and unreliable airspeed), and the aircraft was in the climb phase, application of normal thrust would have led to excessive speed instead of increasing altitude. In either scenario this would also have led to an urgent requirement to retract flaps due to overspeed limitations, allowing MCAS to activate (if it had not already done so).

Nowhere in the Boeing/FAA emergency AD was the requirement to disable auto-throttles, particularly in the event of MCAS activation immediately after takeoff. This may have been because auto-throttles still provide protection in other flight regimes. IMO this inadvertently led both sets of crews down a 'box canyon', where they could not regain control nor pull-up, due to excessive loads on the horizontal stabiliser. As the WSJ article and recent simulator tests imply, all of the well-meaning advice may have been nonsense in the light of actual events.

Edit: CurtainTwitcher gives a better explanation of the speed issues.

Edit: Peter Lemme made this point last week as well: https://www.satcom.guru/2019/03/aoa-...oeing-fix.html
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Old 3rd Apr 2019, 08:25
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Originally Posted by fgrieu
So according to the WSJ (paywalled, but regurgitated by Reuters) the pilots of ET302 applied the 2018-23-51 EAD to some degree, flipped the trim switches off, could not correct the nose down condition (or is it move the trim wheel nose up), then flipped the trim switches back on (contrary to the EAD), to no avail.

I ask (because I don't know):
- How hard it is to manually trim nose up, depending on airspeed, current elevator position, AoA..? I have read about an elevator blowback issue, but do not know the details.
- If standard simulator training prepares to that procedure, complete with simulation of how hard it is to turn the wheel. This is critical: If pilots are not well trained to trim up by manual action on the wheel, then mandating them to make it the only way to trim up was nonsense.
once you trip the cut out switches you remove ALL electric trim, whilst there is no NNC that directs you switch them back on again it would be the only way to regain electric trim, by that stage they were probably point at the ground and assuming pulling in the yoke for dear life, the problem is that if you have full back pressure the electric stops anyway, it will restart trim if you release the back pressure but thatís counter intuitive when pointing at the ground.
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Old 3rd Apr 2019, 08:58
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Originally Posted by Pearly White
On 'sailplanes' lowering the nose is really your ONLY available technique to recover from a stall. Take a glider pilot and put her/him into light single, stall it and their reaction will always be to point the nose at the ground before reaching for the throttle lever.

But on a jet, adding thrust will also change AoA by increasing speed which will change the angle of the airflow over the wings, will it not? I'm not advocating a thrust-only recovery approach, but surely you can do two things at once, lower the nose AND increase thrust? It's not a binary choice.
Of course you can, and should , do both at once. That is why I clearly stated reducing A of A ( to a value just below stalling angle judged by cessation of buffet or stick shaker) by use of elevator and SIMULTANEOUSLY adding full power. Any pilot who cannot do that simple and but vital technique should not be flying anything let alone a jet transport.

When acting as a gliding instructor I have not noticed students from powered flight reaching for the non existent throttle or vice versa when instructing in light aircraft.

Last edited by RetiredBA/BY; 3rd Apr 2019 at 11:23.
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Old 3rd Apr 2019, 08:59
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Originally Posted by EIFFS
assuming pulling in the yoke for dear life, the problem is that if you have full back pressure the electric stops anyway,
The way I understand the books, including the AMM diagrams, the column cutout switches stop opposing electric trim only. Pull back, can't trim forward, push forward, can't trim back.

But like I say, that's just from the books, if you've tried it on the real thing and it is the way you say, then I'll defer to that.
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Old 3rd Apr 2019, 09:05
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FAA declined to comment on the European document. A trim-related "equivalent level of safety" (ELOS) memorandum listed in its 737 MAX certification document is not available on the FAA website. The agency declined to provide it to Reuters.
In a way this was a statement that I was waiting for. This based on my earlier question about what the effect of ODA was on the public availability of certification process documents.

In my view a set of core certification documents should be publicly available, this not depending on who is the operational party doing the certification. There are multiple reasons for that. So in the special case that an accident happens such documents should be directly available in the public domain. And such documents should not be withdrawn from the public domain in the case of accidents. Transparency is key in aviation safety. So declining to provide a document to a reputable agency like Reuters should be accompanied by a very well founded explanation by the certifying authority involved.

In my view it would be unacceptable to hide behind 'the investigation' in such 'public document' cases.
It would also be unacceptable to decline for proprietary reasons if the document would be defined as a public document.
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Old 3rd Apr 2019, 09:30
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Somewhere further back in this thread I thought read that pulling full back on the MAX did not cut out the electrics to trim motor? . This is different from the 737 NG.
I this correct ?
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Old 3rd Apr 2019, 09:59
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Apart from still being in shock after reading those last few truly frightening posts...
A question:
Where in the certification requirement is the overlaying and stacking of both warning, activation of and/or inhibition of, flight control safety systems discussed ?
This surely is covered in detail since the (discovery/understanding) of cognitive overload issues.
Also 2nd an 3rd segment climb phase seems to have been given insufficient cockpit workload attention for combinations of crew and systems errors.

E.G. Stick shaker activation surely should at least have precluded the need for repetitive MCAS intervention...
this combination MUST have been foreseen and particularly for this early flight regime.

And on a panoramic overview scale, if MCAS implementation, let alone its Certification, once 2.5į chunks of stab trim were first proposed, every single authority and engineer involved should have had their hackles raised; better sleepless nights and fractious debate back then...
than regrets now!

"Where have all the good men gone ?

Up where the mountains meet the heavens above
Out where the lightning splits the sea
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Through the wind, and the chill, and the rain
And the storm, and the flood
I can feel his approach in my blood "

Apologies for that...
But 'The Hero' was needed and either MIA or possibly found wanting ☹

Last edited by HarryMann; 3rd Apr 2019 at 10:14. Reason: Improvement
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Old 3rd Apr 2019, 10:10
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@A0283 , post 555

The document can be found on EASA site > documents library > B 737 MAX > IM.A.120 Boeing 737 TCDS appendix ISS 10
Page 15.
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Old 3rd Apr 2019, 10:33
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Originally Posted by VNAV PATH
@A0283 , post 555

The document can be found on EASA site > documents library > B 737 MAX > IM.A.120 Boeing 737 TCDS appendix ISS 10
Page 15.
FYI, it is possible to embed a link to a document directly into a forum post: https://www.easa.europa.eu/sites/def...20ISS%2010.pdf
The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts.

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Old 3rd Apr 2019, 11:52
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Originally Posted by joig
Somewhere further back in this thread I thought read that pulling full back on the MAX did not cut out the electrics to trim motor? . This is different from the 737 NG.
I this correct ?
Partially. Over on tech-log someone posted a diagram for MAX vs NG column switch modules, I cannot vouch for the authenticity, but it appears to show quite clearly that:

IF (only if) MCAS is engaged
___THEN for the aft column cutout switch (only)
______BYPASS the switch (and therefore make it ineffective)
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Old 3rd Apr 2019, 14:25
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Originally Posted by infrequentflyer789
Partially. Over on tech-log someone posted a diagram for MAX vs NG column switch modules, I cannot vouch for the authenticity, but it appears to show quite clearly that:

IF (only if) MCAS is engaged
___THEN for the aft column cutout switch (only)
______BYPASS the switch (and therefore make it ineffective)
i can see their logic there....but believe it ignores the fact that (presumably) such heavy aft stick forces would be used that no sensible pilot would continue exerting them... if they thought they were anywhere near the stall !
So justify leaving the Bypass alone... it's only yet another alteration to a known existing system, fingers off!!
Happy to be corrected...
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Old 3rd Apr 2019, 15:44
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Originally Posted by infrequentflyer789
The way I understand the books, including the AMM diagrams, the column cutout switches stop opposing electric trim only. Pull back, can't trim forward, push forward, can't trim back.

But like I say, that's just from the books, if you've tried it on the real thing and it is the way you say, then I'll defer to that.
what you state is also correct, but in the sim ( level D FFS) at full back you canít trim back unless you release the back pressure, then it starts to trim again ( obviously with cut out switches in normal position)
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Old 3rd Apr 2019, 15:51
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Added to which if AT sesnses a low speed ( real or false) it will increase thrust if engaged further adding to your problems if you are already pointing at the ground
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Old 3rd Apr 2019, 22:23
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Sydney Morning Herald from CurtainTwitchers's post above: "On the 737 MAX, Boeing removed the "yoke jerk" function that enabled pilots to disable the automated trim system with a hard pull on the control column rather than hitting two cut-out switches on the centre console. In a blog post on his personal website, former Boeing engineer Peter Lemme said that could make things harder for a pilot in a crisis. "In the scenario where the stabiliser is running away nose down, the pilot may only fixate on pulling the column back in response," he said. "They may not be mentally capable to trim back or cut out the trim - instead they just keep pulling."
Is there any way to bring the "yoke jerk" back to the Max? Maybe with a harder pull, so normal MCAS response isn't affected?

AoA vanes keep failing, https://www.heraldnet.com/nation-wor...-had-problems/ Got to handle that in Fault Detection & Isolation software well. Even when 2 AoA vanes freeze up to about the same AoA reading! --> 2014 Lufthansa 1829 - Bilbao.

Looking at several accidents like these Max ones, incidents including Qantas 72 (
), etc., what's needed is an easy, quick, one-button (shielded) way to tell the airplane: Turn off all automatic movements of any aero control surface and throttles. Pilot only, proportional control, direct and quickly done.
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Old 4th Apr 2019, 13:59
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I am not able to post URLs so i suggest a search on the term

Incident: Sunwing B38M near Washington on Nov 14th 2018, multiple system failures

Hope this helps
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Old 4th Apr 2019, 14:09
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Arydberg: Was it this one:
Incident: Sunwing B38M near Washington on Nov 14th 2018, multiple system failures
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Old 4th Apr 2019, 15:17
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Yes , That is the one. i cannot post the URL
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Old 4th Apr 2019, 15:21
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Originally Posted by Arydberg
I am not able to post URLs so i suggest a search on the term

Incident: Sunwing B38M near Washington on Nov 14th 2018, multiple system failures

Hope this helps
I did not find any detailed information in the article when I previously read it.

IMO it is perfectly possible to have AOA disagree with all the alarms, but without MCAS activation, if the faulty AOA data is nose down rather than nose up.
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