B737 Max : CAA bans from UK airspace; Comair aircraft grounded
Mar 11, 2019, 2:50 pm
#46
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the memory actions for a runaway stabiliser trim are very clear and short and include disengaging the autopilot (if engaged), moving both stab trim cutout switches to cutout, and trimming manually.
i haven’t see anything which suggests the auto throttle system was malfunctioning for the lion air incident so no reason to touch that.
Mar 11, 2019, 3:04 pm
#47
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my understanding is that it does not operate once the switches are at cutout. I haven’t read pprune so not sure what has been said on there.
Mar 11, 2019, 3:09 pm
#48
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comair have announced on Reuters they are grounding their 737max aircraft (so following China, Indonesia, Caymans, Ethiopia. Royal Air Maroc’s slso grounded).
Mar 11, 2019, 3:34 pm
#49
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My understanding is that MCAS is only enabled when a) the autopilot is not engaged and b) the flaps are retracted. Whilst it does command a nose down attitude and that will not be affected by yoke inputs, it should be overridden by either a) disabling the system or b) manual trim input.
The idea behind the system is eminently sensible to counteract unexpected changes in the pitch of the aircraft.
However, the main issue (based solely on Lion Air) is that it is reliant on the AoA sensors and there are only 2 of them. If one of he sensors provides erroneous information you would expect that the system would deactivate. It appears this is not the case and requires manual deactivation. The sensible fix would be to amend the system such that disagreement between the 2 sets of data provided automatically deactivates MCAS.
This would, I believe, be similar to Airbus whereby if 1 (of 3) systems is in disagreement it is ignored and if 2 (out of 3) fail then “Normal Law” is deactivated and it is for the pilots to manually control the aircraft.
There’s a bit more on MCAS here
The idea behind the system is eminently sensible to counteract unexpected changes in the pitch of the aircraft.
However, the main issue (based solely on Lion Air) is that it is reliant on the AoA sensors and there are only 2 of them. If one of he sensors provides erroneous information you would expect that the system would deactivate. It appears this is not the case and requires manual deactivation. The sensible fix would be to amend the system such that disagreement between the 2 sets of data provided automatically deactivates MCAS.
This would, I believe, be similar to Airbus whereby if 1 (of 3) systems is in disagreement it is ignored and if 2 (out of 3) fail then “Normal Law” is deactivated and it is for the pilots to manually control the aircraft.
There’s a bit more on MCAS here
Mar 11, 2019, 4:04 pm
#50
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Oh, dammit, I've posted that on PPRuNe. I wonder how long that will last!
https://www.pprune.org/10414149-post460.html
https://www.pprune.org/10414149-post460.html
Please let us know what reaction you get over there.
Mar 11, 2019, 4:13 pm
#51
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Mar 11, 2019, 4:13 pm
#53
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It's rather like software. You can add patches, new code and whatever else over an old system, or you can write something completely new from scratch. Both will achieve the same result but (assuming you write it properly) one will be far simpler, easier to troubleshoot and less likely to go wrong every time you add something new to it.
Mar 11, 2019, 4:41 pm
#54
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Mar 11, 2019, 6:17 pm
#56
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As you will see if you read my post, I have already acknowledged the possibility of a type substitution on this sector. Given the relative numbers in the Comair fleet, I think your advice (given you have zero knowledge of the overall itinerary, purpose of travel, number of travellers etc.) is, let me put this politely, ill-founded, extreme and unlooked-for.
Last edited by cauchy; Mar 11, 2019 at 6:27 pm
Mar 11, 2019, 6:35 pm
#57
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News just in: MEXICO'S AEROMEXICO SAYS HAS DECIDED TO SUSPEND THE OPERATION OF ITS SIX BOEING 737 MAX 8 PLANES UNTIL IT HAS CLEAR INFORMATION ABOUT ETHIOPIA INVESTIGATION
Mar 11, 2019, 7:41 pm
#59
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For me, the question is can we at this point say, for sure, it’s not caused or contributed to by aircraft malfunction? If not, I’d personally rather wait until that point arrives before flying on one.
Mar 11, 2019, 8:24 pm
#60
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The disturbing part of this from the pprune thread is that with runaway trim during takeoff, both pilots need to pull back with considerable force (60kg I think) AND find and follow a checklist AND flick a switch, while heading groundwards fast. it seems a difficult situation to manage to put it mildly.
If this crash turns out to be similar to Lionair (which itself hasn't been proved to be MCAS yet) then it's a serious design defect. I imagine the FDR and CVR will be looked at very expeditiously and we'll be told soon. Personally I'd be very wary of getting onto a 737 max until this has been done.
If this crash turns out to be similar to Lionair (which itself hasn't been proved to be MCAS yet) then it's a serious design defect. I imagine the FDR and CVR will be looked at very expeditiously and we'll be told soon. Personally I'd be very wary of getting onto a 737 max until this has been done.