Ethiopian airliner down in Africa

[SLF3]

Only The opinion of SLF, but the issue is not MCAS. The issue is the position of the engine relative to the wing. MCAS is a bandaid on an open wound to get around a rational regulatory requirement.

Boeing should not have proposed the Max, and the FAA should not have accepted it. It is a fundamentally flawed design.

i remember reading an article when the neo was announced which postulated that Boeing would not be able to match it with an upgrade of the 737 because it would require a redesign of the undercarriage to get the necessary ground clearance for the engines. So the design issue was obvious to that much maligned species, a journalist, from the start. Boeing and the FAA knew.

This goes way beyond MCAS. It is about the engineering conscience of Boeing and the independence and competence of the FAA.

[SMT Member]

Let's not forget why MCAS was born: To make the Max feel the same as the NG at the extreme end of the envelope, thus allowing for a common type rating and 1-hour CBT conversion course. This in turn allowed Boeing to use the common rating as a marketing tool.

There are rumours afloat, that the contracted Boeing signed with SW had a clause saying Boeing would pay SW 1 million USD for every aircraft delivered, if sim training was necessary to convert from NG to Max. That's 280 million good reasons why a bean counter and lawyer driven company would come up with an idea such as MCAS.

To my mind there is 'simple' set of possible solutions to this problem:

1: Ditch MCAS
2: Restore stability and stall characteristics to an acceptable level through sound aerodynamic means
3: Forget about the common type rating; this is not your grandfathers 737 so stop pretending it is

[Airbanda]

Originally Posted by LowObservable

Woof woof, it's dark here....

So the dog that hasn't barked, as far as I know, is this:

Aside from the three-crew Lion Air flight that preceded the mishap flight, where are all the crews who might have experienced an AoA failure that triggered MCAS at flaps-up, and handled the situation safely?

For this to happen means that one of the AoA sensors has to be bad from the start, that it has to be bad enough to call a spurious stall warning, and it has to be the sensor that is driving MCAS on this flight (the last being a 50:50 chance). How often has this happened in the MAX's history? I have not seen a single such account in this long thread (I stand corrected if I missed one).

Clearly, that number would provide some valuable context to the two occurrences when the result has been fatal.

Was about to post same question. Have other incidents been reported?

[bill fly]

Grounded Fleet

Can anybody report whether any kind of functionality checks are being performed on the grounded fleet?
eg. Wiring/ FOD/ AoA etc. Plenty of time now for that..

[Gegenbeispiel]

Originally Posted by George Glass

The B737 is a very simple aircraft with lots of bells and whistles, most of which are nice to have, not must have.

The original B737 may have been that, the MAX is not. If it were. you wouldn't need MCAS to certify.
AFAIK, the MAX is certified as a B737 amendment. That may be wrong. If MCAS is necessary to certify, the aerodynamics are radically different.

[Derfred]

Originally Posted by Airbanda

Was about to post same question. Have other incidents been reported?

Well, one was, just a few minutes ago:

Originally Posted by astonmartin

I’ve had a false stick shaker on the B737 during rotation at take-off once. I agree with others that this is a huge distractor. After confirming that it is false, and change of controls, it is not only distracting, but also annoying.

The poster hasn’t stated what caused the stick shaker at rotation, it could have been rogue AOA, but it could also have been something else.

Also didn’t state whether it was a MAX and caused MCAS.

[DaveReidUK]

Originally Posted by coaldemon

they went through VMO within about 2 minutes. From there they kept accelerating. All the way to 500 kts

No, they didn't "keep accelerating". They flew at or around Vmo for almost 3 minutes. It was only in the last 30 seconds of the flight, as they were rapidly losing altitude, that airspeed got anywhere near 500 kts.

[George Glass]

Gergen,
I beg to differ. MCAS is only there to ensure the control column force required to increase pitch does not decrease at high angles of attack.
It is a certification requirement. The aircraft will fly perfectly happily without it.
Disconnect and fly the aircraft.

[abdunbar]

Originally Posted by EDLB

+1

The 737 safety philosophy means that it turns into a conventional stick and rudder aircraft once you turn the AP off. And that with redundant left and right seat set of controls. The PF assumes in AP off mode that he has full authority on the flight controls and surfaces. There are automatic flap retract in over speed left but that does not reduce his controll over the aircraft.
If you brake that philosophy by introducing “features” overriding PF control inputs they need to be full FBW worth with all fail safe features needed for a FBW control.


With the two accidents it came out, that the manual trim wheel can not be actuated manually in a high elevator deflection and high speed situation.

Your first point is the heart of the matter. When faced with any aircraft control problem, the pilot needs to be able to quickly revert the aircraft to a configuration in which he knows what he is dealing with. In the old style mechanically controlled planes such as the 737, this was easily achieved with the autopilot disconnect button. Further, old guys like myself, grew up with these systems. I started flying transport category aircraft when an autopilot was simply a wing leveler and pitch or altitude hold. Manual flight was routine for climbs and descents. My generation needed to be encouraged to embrace auto flight as it matured. We were spring loaded to dump it and manually fly if we got behind. As the years moved on we started to have new/younger pilots whose only experience was systems, auto flight and flight management computers that could handle all phases of flight except initial takeoff. We were encouraged to use these systems fully to reduce workload and to increase our ability to maintain a lookout for traffic, terrain, volcanic cloud, cb, whatever. This advancement was wonderful but it also came with a problem. Over time, hand flying skill and instrument scan was degraded, especially in those who did not have a lot of experience hand flying in vertigo and anxiety inducing circumstances. This resulted in a disability where autoflight could, depending on the individual, become a crutch rather than a tool. The pilot with this disability needed, in any crisis, to first get auto flight operating. This is not a big problem in most circumstances but is a very big problem when the issue is basic aircraft control.

To your second point. I do not know if this is a fact and it seems like it should have been a certification issue if it is. I would not accept any simulator demonstration but would expect that it has been demonstrated in the actual aircraft that the manual, hand crank, stab trim is operable throughout the envelope of the aircraft, speed up to Vmo, altitude, thrust setting, g loading, Cg. If this was not done, it is a problem. If there is a speed limit to manual stab operation, the pilots should be told, even it is just a note that it was not demonstrated to work in excess of Vmo , or whatever speed it was tested to.

[Richard C]

Originally Posted by Derfred

Well, one was, just a few minutes ago:



The poster hasn’t stated what caused the stick shaker at rotation, it could have been rogue AOA, but it could also have been something else.

Also didn’t state whether it was a MAX and caused MCAS.

If you had the shaker on rotate, you wouldn't be raising the flaps in a hurry so at least MCAS wouldn't start retrimming the plane at low altitude.

[MemberBerry]

Originally Posted by Albino

You need to go and read step 2 again. It wasn't completed, at any point after the MCAS AND.

One could argue that you can skip step 2 when the A/P is not engaged.

I don't think the runway stabilizer memory items cover all possible runway situations properly, especially when MCAS is involved. A step 2.5 asking you to try to bring the trim back to neutral using the thumb switches, before applying the cutoff switches, wouldn't hurt, in my opinion.

And having in mind that the current version of MCAS will re-activate in 5 seconds, it should also tell you to use the cutoff switches as soon as possible after you bring the trim to neutral, in under 5 seconds after your last electric trim use. With the new MCAS version that will hopefully no longer be needed.

There are plenty of things the accident crew could have done better, and they clearly made mistakes. I think using the cutoff switches before bringing the trim to neutral was one of their smallest mistakes, if you can even consider it a mistake.

Boeing and the FAA claiming, after the Lion Air crash, that the existing procedures for dealing with a runway stabilizer are sufficient to address the MCAS issues is a much larger mistake, in my opinion.

And the elephant in the room is that manual trimming with the trim wheels can be extremely hard, or even impossible to do, when you apply a lot of nose up elevator depending on the airspeed.

In addition to the MCAS fixes, I think this is one of the problems the FAA and Boeing need to address, not only for the MAX, but for previous models as well.

Unfortunately I don't see an easy solution for that particular problem. Some complex changes might be needed. For example an additional electric trim circuit and motor as a backup for the main one.

[Richard C]

Originally Posted by George Glass

Gergen,
I beg to differ. MCAS is only there to ensure the control column force required to increase pitch does not decrease at high angles of attack.
It is a certification requirement. The aircraft will fly perfectly happily without it.
Disconnect and fly the aircraft.

That seems to be the problem - you can't disconnect MCAS without defeating the trim motors and there now appears (from the ET report) to be a problem in retrimming manually with a lot of back-stick. The other way would be to run down a stage of flap, which should stop MCAS interfering but it's hard to see a procedure which called for that getting approval.

[Derfred]

One could argue that you can skip step 2 when the A/P is not engaged.

Seriously?

Aircraft is trimming badly forward when you don’t want it to. Try trimming it back then trim cutout. If that doesn’t work then trim cutout anyway. You’re a pilot.

[MemberBerry]

Originally Posted by Derfred

Seriously?

Aircraft is trimming badly forward when you don’t want it to. Try trimming it back then trim cutout. If that doesn’t work then trim cutout anyway. You’re a pilot.

I'm not saying it's a correct argument, personally I don't think you should skip step 2, but I've seen some people arguing that. So there is some confusion about those memory items.

But, in any case, the problem is you have only 5 seconds to use the cutout switches before MCAS does it again. If you delay that by only a few seconds, you end up with an out of trim aircraft. No matter how you look at it, that is not ideal.

And the Ethiopian crew did trim it back partially before using the cutout switches. They probably felt the trim they applied was sufficient to make the aircraft controllable enough at that point, and didn't want to risk applying more with the stick shaker active.

And assuming it's not MCAS, but a regular trim runaway that can't be stopped or reversed with the thumb switches, you will be out of trim after using the cutout switches. Both on the MAX and also on older models. Not easily being able to then correct the trim with the trim wheels in that situation is a big problem.

My point is that, even if you don't skip step 2, and I don't think you should skip it, you can end up in the same situation they did, depending on the type of runaway you are experiencing.

[gmx]

Originally Posted by GordonR_Cape

2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?

​​​​​​A disconcerting mystery is why the crew of the preceding LionAir flight didn't feel like they had miraculously dodged an insidious malfunction, and instead handed the aircraft to the next crew with little warning of the mortal danger that lay ahead. And why the airline allowed the vehicle back into the air after an emergency had been declared on that preceding flight, without fully understanding the nature and source of the flight control issues experienced.

For some reason I'm less concerned about the automated flight control issue than the fragility of the safety processes enacted in the event of a declared emergency. If that Lion aircraft had been grounded immediately following the pre-accident flight ...

[Albino]

Originally Posted by MemberBerry

One could argue that you can skip step 2 when the A/P is not engaged.

Just to confirm, I'm talking about 'Control airplane pitch manually with control column and main electric trim as needed'

This is pretty basic stuff.

[Ian W]

Originally Posted by GordonR_Cape

I agree that such data would be very useful, but suggest two reasons why it has not been forthcoming:
1. If AOA fails nose down (50% odds), there will be no stick shaker or stall warning or MCAS activation, and it would probably be a non event, written up for maintenance, or reported to the NASA hotline. Conversely if AOA fails nose up on the 'non-MCAS' side (25% odds), there will be stick shaker activation, but it will not be flight critical, and the fault will be repaired. In neither case will the airframe be examined in any detail.
2. In the event of AOA failing nose up and MCAS activating (25% odds), there is an overwhelming fatality rate. There are no known survivors other than the preceding Lion air flight, and unfortunately that airframe was destroyed the very next day, so there is little evidence to strip down and examine (apart from the FDR).
Does this provide some context on the relative scarcity of such occurrences?

As was stated before the AoA vanes are not new equipment and are the same on all the NGs and probably the Classic. There are vast numbers of these flying and as you state they would be just maintenance issues, but all those issues go into analytics and Boeing would have known their failure rate on designing the Max. In knowledge of that failure rate they felt failures were improbable to highly improbable. They also felt that a crew given significant uncommanded nose down trim would immediately trim back nose up and a second uncommanded nose down would result in the crew trimming back nose up then switching off the Stab Trim. It was certainly not expected that a crew would attempt to fly with significant pull force and _not_ trim back. As someone upthread stated trimming is second nature. So add to your probabilities extremely rare failure of AoA vane and Full expectation that 99.9% of PF would trim back to in trim if MCAS did operate incorrectly giving significant uncommanded nose down trim and after 2 or at worst 3 trim back would switch off Stab Trim.

[Rananim]

The MCAS put the aircraft into an almost (or totally) unrecoverable situation at low altitude and no BS about untrained inexperienced pilots is worth a pinch of rocking horse poo.

Sunfish

I cannot concur here.
The Boeing software design error is proven and accepted. Thats not the point here though.This crew did not fly the plane. Single side UAS after takeoff is not difficult.The stick shaker is a huge distraction but they are commercial aircrew acutely aware of the Lionair precedent.They know about MCAS and how it can be triggered in manual flight with flaps UP.Like all good aircrew they will have formulated a plan of action which will help them focus and overcome the danger of the stick shaker and its effect on the human brain's ability to think.
They will brief on what they will do....for every departure!
ISFD and FO ASI are functioning and in agreement.The Captain need only hand control to the FO and instruct him to fly a manual visual pattern at 1500 keeping takeoff flap
setting and land immediately..Right hand on the stick,left hand on the thrust levers,feet guarding the rudders.Fly the plane.
Boeing UAS NNC not applicable here! Just land the plane.

[CodyBlade]

Good info here:

https://theaircurrent.com/aviation-s...nvestigations/

[Richard C]

Originally Posted by CodyBlade

Good info here:

https://theaircurrent.com/aviation-s...nvestigations/

Thanks for the link - very disturbing info.