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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 12th Mar 2019, 09:05
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Australia has suspended operations of all Boeing 737 Max aircraft

https://www.rte.ie/news/world/2019/0...irlines-crash/
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Old 12th Mar 2019, 09:06
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In fifteen years on the 737 I cannot remember using the stab trim cutout switches apart from in the sim and even then only very occasionally. If the pilot flying was confronted with a similar scenario to the Lion accident then the combination of startle, unfamiliarity with the aircraft and a very new co-pilot could plausibly lead to this kind of end result.

The statements from Ethiopian about ‚senior captains‘ with a couple of months experience on the airplane and first officers with 200 hours are not terribly reassuring. There is no ‚single size fits all‘ solution to minimum experience levels for pairing new pilots. But it would be surprising if this did not play a role.

Finally Boeing‘s experience with electronic systems and stabilizers has not been uniformly happy. The MD11 which they inherited from Douglas had well reported issues in this area. This looks to be quite unrelated. But if I was a Boeing lawyer, aside from leafing through new sailboat catalogues in anticipation of massive billable hours, I would be looking into who was responsible for the MCAS development and implementation.
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Old 12th Mar 2019, 09:10
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Originally Posted by Chesty Morgan
For clarity it was an option on Boeings (might be 737 only) to have it either way.
I've flown ex Lufthansa 737s one day and ex Ansett the next where switches operated in the opposite sense. Didn't take much getting used to.
I don’t think switch direction was a Boeing option. Ansett demanded the switches all be reversed, so that all their fleets had the switches operating in the same direction - to prevent the very confusions we are talking about. But I thought there were some hard negotiations about this - it was never a Boeing option.

Silver

Last edited by silverstrata; 12th Mar 2019 at 09:47.
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Old 12th Mar 2019, 09:21
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Its a long time since I flew. a 737, ( 200 and 300) but is it the case that the Max system is capable of driving the stab. to FULL deflection .
Time dims the memory but IIRC. The 73 75 and 76 and other types I have flown, that was not the case, in fact stick pushers only moved the elevators, stabs were not moved.

Surely switch direction of the stab trim cutout switches is irrelevant, if something is ON. to switch OFF. Simply move the switch(es) away from that position !
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Old 12th Mar 2019, 09:25
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Originally Posted by lederhosen
In fifteen years on the 737 I cannot remember using the stab trim cutout switches apart from in the sim and even then only very occasionally. If the pilot flying was confronted with a similar scenario to the Lion accident then the combination of startle, unfamiliarity with the aircraft and a very new co-pilot could plausibly lead to this kind of end result. The statements from Ethiopian about ‚senior captains‘ with a couple of months experience on the airplane and first officers with 200 hours are not terribly reassuring. There is no ‚single size fits all‘ solution to minimum experience levels for pairing new pilots. But it would be surprising if this did not play a role.
Ditto that. With more than two decades on the B737 I too have never had recourse to have to move the Stabiliser switches to CutOff. And total hours are not a measure of competence; e.g. thousands of hours poling about in a normally highly-reliable-where-nothing-ever-goes-wrong aeronautical chariot does not necessarily turn someone into a latter day Chuck Yeager,
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Old 12th Mar 2019, 09:28
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A few things noticed: MCAS seems to be a fast_put_together SW solution to a certification problem (stick force/g). Not a stall preventer directly. It also looks like B forgot to include data validity checks and "reasonables" checks that would return any trimming actions done after AoA returns to safe range.

A thought I had when reading what STS does, that sounds like SW augmented longitudinal stability. Meybe B thought that when that was acceptable other similar patching would be ok too.

Maybe they really should retire the 737 base and have a new one (yes, that does cost a lot), design methods have advanced a lot since the first flight of 737, which I understand was a good airliner in its first versions.
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Old 12th Mar 2019, 09:28
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Originally Posted by Callsign Kilo
.
Someone mentioned that the MCAS provides 10 secs of trim input when activated. Can that be correct/verified? 10 secs of trim input is massive on the 737.

Was this not the contributing factor in the FlyDubai 738 crash in Rostov?

Yes, that is correct - 10 seconds, or 2 degrees forward, for each operation of MCAS. And after 5 seconds, you get another 2 degrees of trim, until you end up with full forward trim. It was designed for slow speed, but if it happens inadvertently at high speed, you could be in the sh1t. Imagine this happening up in coffin corner, and you suddenly get 10 seconds of pitch - even the quickest of crews disconnecting the stab-trim would still result in an overspeed incident. And I can tell you the aircraft shakes a lot - we had an autopilot failure which pitched the aircraft down by 5 degrees. The recovery was smooth, but the high spoeed buffet was considerable.

But I still cannot imagine why or how this MCAS system was ever certified by the FAA. Even if MCAS operated at the right time, in a stall condition, who on earth would want full trim forward when pulling out of the subsequent dive? We tried it in the sim, and concluded it was impossible to recover from the dive. So the system that is supposed to save you, saves you and then kills you.

Rostov.

I have been wondering about Rostov. Is it possible that the Fly Dubai was fitted with a Max speed-trim computer? I bet they are compatible, because that is cheaper, and Boeing does everything on the cheap. So did an engineer not have the right spare unit, so fitted one from a Max instead? - Not realising that there was a fundamental software difference between the two units?

I wonder because the report said that the Fly Dubai pilots trimmed forward for 10 seconds. And everyone was aghast by that news, because no pilot would ever trim forward for 10 seconds. We were thinking in terms of a health issue, with someone freezing on the controlls. But as it happens, this is exactly what MCAS does - it trims forward for 10 seconds. So was the Fly Dubai fitted with a Max speed-trim computer?

Silver

P.S. If Boeing had fitted a stick-pusher, none of this would have happened. A stick push operates on the elevator, not the stab, and is more easily overcome with stick force. More importantly, when a stick-push relents (by either a stall recovery or a cutout), the aircraft is instsantly in trim. But with a trim-pusher you are way out of trim, and it will take you 30 seconds to trim back to the normal position. You may not have 30 seconds left. (But if course a stick-pusher would have cost money, and lots of certification time...)





Last edited by silverstrata; 12th Mar 2019 at 10:01.
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Old 12th Mar 2019, 09:28
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Originally Posted by jolihokistix
Interesting yes, but if they can write this with a straight face... "Malaysia Airlines, which the public viewed with misgivings after it lost two 777s in less than five months in 2014. Though it bore no obvious responsibility for either incident—one was shot down by Russia, the second was hijacked..." how deep will the rest of it be?
Pretty accurate. One was shot down by a Russian missile and the other was (almost certainly) hijacked by its captain .......
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Old 12th Mar 2019, 09:32
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A layman's explanation of MCAS

Originally Posted by cooperplace
yep, I sure as hell don't and I'd love to see it explained in a way so that a dimwit like me (LSA pilot) can understand.
In reference what people are discussing here it's fundamentally straightforward, albeit perhaps not easily explained without a piece of paper - let me see if I can provide a suitable analogy:

If you were to push a small (non power-steer) car somewhere near the middle of its boot (you're in Oz so I don't need to say 'trunk' :-) it would travel in a relatively straight line along a flat road without much input from the driver.

If you then moved that push/thrust off-centre (let's say to the right) and started pushing, the vehicle would want to drift gradually to the left if it weren't corrected by the driver via the steering wheel.

If you pushed harder, and/or you moved to the right-hand extremity of the boot then the vehicle would have a significantly greater left-hand drift which could require considerable correction by the driver, and even catch them unawares.

MCAS on the 73-MAX is a little as if you installed automatic centering power steer to this car so that an off-centre push wouldn't cause it to drift off-line significantly and wouldn't require much, if any, effort/correction by the driver.

To move from the analogy to the reality; as the MAX has significantly more thrust (push) than earlier 73 models, and that thrust is further out (down) from the centre of the aircraft (in elevation) it will want to pitch up significantly when power is applied. This is not a good thing and so without major re-design of the control surfaces or airframe MCAS is a system that takes data from an Angle-Of-Attack (AOA) sensor and corrects for this undesirable pitch up by trimming down, should it 'see' the aircraft deviating from its true path. It does this without specific input from the pilot.

There's clearly somewhat more detail around the actual operation/methodology of MCAS as we understand Boeing's implementation, but I think this gives the essence of it?

FP.
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Old 12th Mar 2019, 09:41
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U.S. to mandate design changes on Boeing 737 MAX 8 after crashes

U.S. to mandate design changes on Boeing 737 MAX 8 after crashes


WASHINGTON (Reuters) - The United States will mandate that Boeing Co implement design changes by April that have been in the works for months for the 737 MAX 8 fleet after a fatal crash in October but said the plane was airworthy and did not need to be grounded after a second crash on Sunday.

Boeing confirmed the Federal Aviation Administration’s announcement late Monday that it will deploy a software upgrade across the 737 MAX 8 fleet “in the coming weeks” as pressure mounted. Two U.S. senators called the fleet’s immediate grounding and a rising number of airlines said they would voluntarily ground their fleets.

The company confirmed it had for several months “been developing a flight control software enhancement for the 737 MAX, designed to make an already safe aircraft even safer.”

The FAA said the changes will “provide reduced reliance on procedures associated with required pilot memory items.”

The FAA also said Boeing will “update training requirements and flight crew manuals to go with the design change” to an automated protection system called the Maneuvering Characteristics Augmentation System or MCAS. The changes also include MCAS activation and angle of attack signal enhancements.
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Old 12th Mar 2019, 09:44
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Originally Posted by juice
Australia has suspended operations of all Boeing 737 Max aircraft

https://www.rte.ie/news/world/2019/0...irlines-crash/
This affects only two Fiji Airways aircraft after Silk grounded their six 737 MAX 8 aircraft that fly into Darwin and Cairns although it's really hard for Fiji Airways with 2 out their dozen aircraft grounded.
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Old 12th Mar 2019, 09:46
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Originally Posted by RetiredTooEarly
In great VMC conditions - as reported - even the very worst of pilots should surely be able to maintain some semblance of the old Straight and Level.

Seems inconceivable to me that even if this Max had the same airspeed/attitude problems as the last one that crashed, the pilots couldn't have controlled it.
I don’t agree at all.

If the f/o was flying, he only had 200 hours. After flaps up, the stick shaker goes off, which is mighty disconcerning, and MCAS bungs in a load of trim. The captain cannot see why the trim is trimming, and the low-hours f/o has no clue (seen that many times). The captian thinks he has an airspeed problem and is stalling, and tells the f/o to lower the nose - which the f/o does rather easily, because he is holding a load of back pressure. MCAS then bungs in another load of trim, and the f/o is now really struggling with the controls - never having felt an aircraft behave like this (at this stage, you need about 30 kg of force to hold the aircraft level).

The captain is still convinced the airspeed is wrong and they may be stalling (stick shaker still going), and shouts “I have control”, but does not realise so much pitch force is necessary, so the aircraft instantly pitches forward into a steep dive. Captain is mighty startled by this - is this pitch down the result of a stall? He has forgotten all about the previous trim episodes, and just hauls back on the stick. But MCAS now gives another load of forward trim, which makes the aircraft completely unflyable (60 kg of force necessary on the stick). And here comes terra firma....

Silver
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Old 12th Mar 2019, 09:51
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Originally Posted by silverstrata

I have been wondering about Rostov. Is it possible that the Fly Dubai was fitted with a Max speed-trim computer? I bet they are compatible, because that is cheaper, and Boeing does everything on the cheap. So did an engineer not have the right spare unit, so fitted one from a Max instead? - Not realising that there was a fundamental software difference between the two units?

I wonder because the report said that the Fly Dubai pilots trimmed forward for 10 seconds. And everyone was aghast by that news, because no pilot would ever trim forward for 10 seconds. We were thinking in terms of a health issue, with someone freezing on the controlls. But as it happens, this is exactly what MCAS does - it trims forward for 10 seconds. So was the Fly Dubai fitted with a Max speed-trim computer?

Silver
Given that accident was in Dec 2016 to an aircraft built in 2010 and the Max didn't enter service until Aug 2017 I think that's a pretty fanciful hypothesis.
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Old 12th Mar 2019, 09:51
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Originally Posted by silverstrata




Rostov.

I have been wondering about Rostov. Is it possible that the Fly Dubai was fitted with a Max speed-trim computer? I bet they are compatible, because that is cheaper, and Boeing does everything on the cheap. So did an engineer not have the right spare unit, so fitted one from a Max instead? - Not realising that there was a fundamental software difference between the two units?

I wonder because the report said that the Fly Dubai pilots trimmed forward for 10 seconds. And everyone was aghast by that news, because no pilot would ever trim forward for 10 seconds. We were thinking in terms of a health issue, with someone freezing on the controlls. But as it happens, this is exactly what MCAS does - it trims forward for 10 seconds. So was the Fly Dubai fitted with a Max speed-trim computer?

Silver
The issue with your theory is that the Rostov accident happened only two months after the Max first flew and at least a year before FZ took delivery of their first MAX, so it is pretty unlikely that a flydubai engineer happened to find a spare MAX component kicking around in a parts bin and then randomly fit it into an 800.
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Old 12th Mar 2019, 09:52
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Something else to ponder is that the 737 is controllable with the trim at either the forward or rear extreme. However, it's a two hands on the column job.
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Old 12th Mar 2019, 09:57
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Australia joins the list:

https://www.bbc.com/news/world-asia-47536502
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Old 12th Mar 2019, 09:57
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Originally Posted by silverstrata


I don’t agree at all.

If the f/o was flying, he only had 200 hours. After flaps up, the stick shaker goes off, which is mighty disconcerning, and MCAS bungs in a load of trim. The captain cannot see why the trim is trimming, and the low-hours f/o has no clue (seen that many times). The captian thinks he has an airspeed problem and is stalling, and tells the f/o to lower the nose - which the f/o does rather easily, because he is holding a load of back pressure. MCAS then bungs in another load of trim, and the f/o is now really struggling with the controls - never having felt an aircraft behave like this (at this stage, you need about 30 kg of force to hold the aircraft level).

The captain is still convinced the airspeed is wrong and they may be stalling (stick shaker still going), and shouts “I have control”, but does not realise so much pitch force is necessary, so the aircraft instantly pitches forward into a steep dive. Captain is mighty startled by this - is this pitch down the result of a stall? He has forgotten all about the previous trim episodes, and just hauls back on the stick. But MCAS now gives another load of forward trim, which makes the aircraft completely unflyable (60 kg of force necessary on the stick). And here comes terra firma....

Silver
Woah!! They should hire you for the inevitable National Geographic over-dramatization.
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Old 12th Mar 2019, 10:02
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Originally Posted by Jeps
I don’t drive the MAX but I think I understand what MCAS does and doesn’t do (maybe). Is it possible that two things could be true and that whilst Boeing have stuffed up on a few different levels as I see it could it also be the case that if training were appropriate neither of these incidents would’ve been fatal?
It is also possible this flight discovered a new failure mode for the software logic.
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Old 12th Mar 2019, 10:09
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Originally Posted by juice
Australia has suspended operations of all Boeing 737 Max aircraft

https://www.rte.ie/news/world/2019/0...irlines-crash/
Well that’s easy. Considering there are none operating in Australia.

Cheaply bought spine CASA!
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Old 12th Mar 2019, 10:10
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Originally Posted by Chesty Morgan
Something else to ponder is that the 737 is controllable with the trim at either the forward or rear extreme. However, it's a two hands on the column job.
and whilst you have two hands on the yoke, the FAA directive to follow the trim runaway memory checklist, requires you to operate the guarded stabilizer trim cut out switches. Maybe the FO can do this. Once done, you still have the aircraft out of trim but now your trim switches on the yoke wont work. You need to shout at the copilot, to operate the trim wheels manually. If way out of trim, he's got plenty of spinning to do. Too much speed? Will reducing thrust result in more pitch down or give more time for the copilot to save the aircraft?
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