Ethiopian Airways flight crashes (10/03) + 737 MAX grounding

Shaw S Hunter · 3 Apr 2019

Boeing's design resources have been largely tied up by the development of the 777x which has finally been rolled out this week. It is now considering whether to go ahead with the NMA (New Mid-market Aircraft) ie 757/767 replacement. At some point very soon it will have to make a final decision on that and in the process start to freeze the options for production. Unfortunately it's not getting the enthusiastic reaction from airlines that Boeing had hoped for though it would certainly win orders: the question is would the number of orders be big enough to justify the cost of development.

It's becoming clear that Boeing really does need to move on fairly swiftly to a clean-sheet design of narrow-body but the reality of modern day airliner design is that it's incredibly expensive and also relies on a significant commitment by engine manufacturers to produce something suitable. And all the major engine manufacturers are going through difficult times presently dealing with persistent niggles with their latest designs. Boeing may well find that its military output will form a rather larger proportion of its profits for a while.

As for Airbus while the failure of the A380 to make any real headway in the market may be a blow to its corporate pride at least the decision to terminate production will leave it free to consider its options in other sectors of the market. It would seem a big question is how it might react if Boeing proceeds with the NMA: one possible cheap win could be a further narrow-body stretch to produce an A322 which would potentially be an almost like-for-like replacement for the Boeing 757.

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Bletchleyite · 3 Apr 2019

Shaw S Hunter said:
Boeing's design resources have been largely tied up by the development of the 777x which has finally been rolled out this week. It is now considering whether to go ahead with the NMA (New Mid-market Aircraft) ie 757/767 replacement. At some point very soon it will have to make a final decision on that and in the process start to freeze the options for production. Unfortunately it's not getting the enthusiastic reaction from airlines that Boeing had hoped for though it would certainly win orders: the question is would the number of orders be big enough to justify the cost of development.

I suppose the thing there is that the 787 takes some of that market, making it smaller.

158756 · 3 Apr 2019

Bletchleyite said:
I suppose the thing there is that the 787 takes some of that market, making it smaller.

Plus there are now 737 MAXs and A321s with similar capacity to a 757 and capable of crossing the Atlantic - between those and the 787 how many jobs are there that really need a 757 or 767 now?

Shaw S Hunter · 3 Apr 2019

158756 said:
Plus there are now 737 MAXs and A321s with similar capacity to a 757 and capable of crossing the Atlantic - between those and the 787 how many jobs are there that really need a 757 or 767 now?

US airlines wanting a particular mix of range and capacity for trans-cons and Hawaiian services but also wanting improved economy ie latest tech engines. It would seem that the A330 NEO has been a failure in that specific market.

WatcherZero · 3 Apr 2019

Wall Street Journal is reporting a leak from unnamed sources that the Ethiopian jet pilots followed Boeing procedure and turned MCAS off, but struggling for control they turned it back on again. If true this flips the incident on its head and opens up whole new crash diagnosis and rectification issues for Boeing.

Some pilots are pointing out that the procedure after MCAS is turned off is to make manual trim control adjustments, however an advisory in the manual for the 737 Classic which was ommitted for the 737 NG and MAX versions was that pilots might experience difficulty moving the flaps via the stabiliser trim wheel if the stick is being pulled back due to counter forces acting on the stabiliser. They are speculating that the MAX stabalisers might be experiencing the same thing.

Also another detail emerging from the simulator tests was that the MCAS system would always win over the pilot in a tug of war because it adjusted by 0.27 units per second while the manual trim adjustment operates at 0.18 unit per second increments.

edwin_m · 4 Apr 2019

It would be several years before Boeing could complete and test a new design and obtain type approva,l particularly given the extra scrutiny they are likely to be under.

In the meantime I should imagine Airbus are looking at how quickly their A380 production lines can be turned over to more A320 series.

sng7 · 4 Apr 2019

The Preliminary Report is now available here: http://www.ecaa.gov.et/documents/20...AVJ).pdf/4c65422d-5e4f-4689-9c58-d7af1ee17f3e
It seems to support the earlier statements that one faulty angle of attack sensor caused the plane to pitch nose down and the pilots turned off the MACS system using the checklist from boeing but could not regain control of the aircraft.

TheEdge · 5 Apr 2019

sng7 said:
The Preliminary Report is now available here: http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+,(ET-AVJ).pdf/4c65422d-5e4f-4689-9c58-d7af1ee17f3e
It seems to support the earlier statements that one faulty angle of attack sensor caused the plane to pitch nose down and the pilots turned off the MACS system using the checklist from boeing but could not regain control of the aircraft.

If the pilots really were doing the right thing as advised by Boeing and still got nosedived into the ground it really is quite a horrifying situation for an airliner to be flying with that sort of fault.

Shaw S Hunter · 5 Apr 2019

TheEdge said:
If the pilots really were doing the right thing as advised by Boeing and still got nosedived into the ground it really is quite a horrifying situation for an airliner to be flying with that sort of fault.

While all the focus has been on the apparently poor implementation of MCAS it should be noted that in both the Lion Air and Ethiopian crashes the first event in the accident sequence was the failure of an Angle of Attack sensor. Given the importance of these devices there will surely need to be some attention paid to the design, installation and maintenance of them. But of course that still doesn't change the fact that MCAS as installed on the MAX puts the automation into an unequal arm-wrestle with the pilots, hardly a recipe for safe operation. Boeing is apparently talking in terms of getting the MAX airborne again within 3 weeks: will other safety authorities be quite so keen?

TheEdge · 5 Apr 2019

Shaw S Hunter said:
While all the focus has been on the apparently poor implementation of MCAS it should be noted that in both the Lion Air and Ethiopian crashes the first event in the accident sequence was the failure of an Angle of Attack sensor. Given the importance of these devices there will surely need to be some attention paid to the design, installation and maintenance of them. But of course that still doesn't change the fact that MCAS as installed on the MAX puts the automation into an unequal arm-wrestle with the pilots, hardly a recipe for safe operation. Boeing is apparently talking in terms of getting the MAX airborne again within 3 weeks: will other safety authorities be quite so keen?

From the information released to the public it sounds like the issue lies in the MCAS not acknowledging the disagreement between the two AOA sensors. The report up the thread details one of the sensors reading 75 degree nose up while the other was reading 15. As others have said it seems very surprising that the system doesn't either revert to pilot control with a disagreement or have some sort of voting logic.

No doubt Boeing and the FAA will be keen to get them airborne again, for both corporate and political pride if nothing else. While I don't doubt the various safety bodies around the world are just as thorough as each other I'm interest to see what it takes for the other, lets say more recognisable boards, like EASA or CAA have to say. Thinking like that is this the sort of thing that IATA or ICAO would ever get involved with?

Bald Rick · 5 Apr 2019

TheEdge said:
No doubt Boeing and the FAA will be keen to get them airborne again, for both corporate and political pride if nothing else. While I don't doubt the various safety bodies around the world are just as thorough as each other I'm interest to see what it takes for the other, lets say more recognisable boards, like EASA or CAA have to say. Thinking like that is this the sort of thing that IATA or ICAO would ever get involved with?

They will be keen to get them airborne again. However they will also be mindful that if they do re-enter service, and another one falls out of the sky, that will finish the type (and possibly the FAA). And given that the 737MAX represents 75% of Boeing’s forward order book, it would finish the company. So they will make absolutely sure it is ready.

ian959 · 5 Apr 2019

From Sky News: Boeing has admitted that a key sensor malfunctioned on two of its 737 Max 8 planes which crashed, killing all on board in separate incidents.

Well, that just opened the way for some serious payouts to the victims of the two crashes and heaps even more pressure on the FAA and their reliance of "self-certification"...

Bletchleyite · 5 Apr 2019

ian959 said:
From Sky News: Boeing has admitted that a key sensor malfunctioned on two of its 737 Max 8 planes which crashed, killing all on board in separate incidents.

There shouldn't be any single "key sensors". There should be three, so if two agree you've got a likely value, and also a "fail safe" situation if more than one fails. The more I hear about this, the more Boeing have blood on their hands through a combination of incompetence and poor management at multiple levels.

edwin_m · 5 Apr 2019

Bletchleyite said:
There shouldn't be any single "key sensors". There should be three, so if two agree you've got a likely value, and also a "fail safe" situation if more than one fails. The more I hear about this, the more Boeing have blood on their hands through a combination of incompetence and poor management at multiple levels.

I was thinking that. If the MCAS is so important then shutting it down would in itself be hazardous, so it needs to keep working in all credible situations but also not react to false sensor readings.

LOL The Irony · 5 Apr 2019

Bletchleyite said:
There shouldn't be any single "key sensors". There should be three, so if two agree you've got a likely value, and also a "fail safe" situation if more than one fails.

My dad is an aircraft engineer and when I told him there was only 1 MCAS sensor, his reply was; "There should be more than one". We also got talking about how the 737 didn't have computers and they were slapped in there unlike Airbus' which were designed to be computer operated from day 1. We also talked about the 15% increases and the fact the 737 needs replacing.

WatcherZero · 5 Apr 2019

I thought there were two sensors on the MAX but the MCAS only took data from one of them, hence the optional extra disagree warning light.

TheEdge · 5 Apr 2019

Boeing now reporting they are slowing MAX production.

Greybeard33 · 6 Apr 2019

There is a technical description of the MCAS at http://www.b737.org.uk/mcas.htm. This is based on Boeing documentation and contributions from pilots and engineers familiar with the aircraft.

There are two Angle of Attack (AoA) sensors, left and right. These are connected one to each of the two Air Data Inertial Reference Units (ADIRUs).

MCAS is implemented as a software function in both of the two Flight Control Computers (FCCs). The FCCs are operationally redundant and independent. FCC1 uses data from the left side sensors, including the left ADIRU, and FCC2 uses data from the right side sensors. MCAS is active in only one FCC at a time; if the active FCC fails, the standby FCC takes over. Normally the active FCC (and so the AoA sensor in use) alternates between successive flights.

If the AoA sensor used by the active FCC fails such that it gives an erroneously high output, it can trigger inappropriate MCAS nose down stabilizer trim. The same failure can concurrently cause inappropriate activation of one of the two stall warning stick shakers; the stall warning system (as on all 737 models) has two independent channels, each using data from one AoA sensor.

The ADIRUs use data from their respective AoA sensors to correct the sensed static pressure used in the computation of airspeed and altitude. So an erroneous AoA sensor can cause erroneous airspeed and altitude on one pilot's Primary Flight Display (PFD) and in the inputs to the related FCC. This causes IAS DISAGREE and ALT DISAGREE alerts on both pilots' PFDs; the pilots can then attempt to determine whose display is correct by comparison with the standby instruments.

The MCAS certification assumed that the pilots would recognise inappropriate MCAS nose down trim as a "Runaway Stabilizer" scenario, and carry out appropriate corrective actions according to the existing checklist applicable to all 737 models. However, the concurrent stick shaker and air data alerts created a high pilot workload that made the situation more challenging.

WatcherZero · 17 Apr 2019

Greybeard33 said:
The MCAS certification assumed that the pilots would recognise inappropriate MCAS nose down trim as a "Runaway Stabilizer" scenario, and carry out appropriate corrective actions according to the existing checklist applicable to all 737 models. However, the concurrent stick shaker and air data alerts created a high pilot workload that made the situation more challenging.

And the Ethiopian correctly followed the procedure and corrective actions for the runaway stabilizer scenario as set out in the checklist, however MCAS was still fighting the pilots.

cactustwirly · 17 Apr 2019

LOL The Irony said:
My dad is an aircraft engineer and when I told him there was only 1 MCAS sensor, his reply was; "There should be more than one". We also got talking about how the 737 didn't have computers and they were slapped in there unlike Airbus' which were designed to be computer operated from day 1. We also talked about the 15% increases and the fact the 737 needs replacing.

Exactly! The design dates from the 1960s, definitely needs replacing!

From what I've read, Boeing completely bodged the 737 MAX, and the corrupt FAA didn't stringently test the MAX, leaving it all to Boeing and their self certification, which was dodgy.

edwin_m · 18 Apr 2019

WatcherZero said:
And the Ethiopian correctly followed the procedure and corrective actions for the runaway stabilizer scenario as set out in the checklist, however MCAS was still fighting the pilots.

However there seems to be a suggestion that they were going too fast, not having reduced the thrust after take-off, and that this would have made the manual trim impossible to use because of the increased aerodynamic forces on the stabiliser. So it appears that as a last resort they re-activated the powered system which also re-activated the MCAS. I guess the speed might in turn have resulted from unfounded concerns about stalling.

Greybeard33 · 18 Apr 2019

The preliminary Ethiopian Accident Investigation Report can be downloaded from http://www.ecaa.gov.et/. It states that the pilots selected the STAB TRIM switches to CUT OUT in accordance with the Boeing checklist. This action killed power to the electric trim motor and prevented MCAS trimming any further nose down, as confirmed by no stabiliser movement in response to a subsequent MCAS command. However, it also disabled electric trim from the switches on both pilots' control yokes, which are the normal means of trimming during manual flight.

The pilots then found they were unable to raise the nose sufficiently by pulling back on the control columns, because the stabiliser was still trimmed nose down from the previous MCAS commands. By this time, with the engines still at takeoff power, the aircraft had accelerated to maximum operating speed (VMO) and the pilots could not trim up manually, using the mechanical trim wheels on the centre pedestal, because the aerodynamic forces were too high. It was physically impossible to rotate the wheels.

It appears that, as a last resort, the pilots moved the STAB TRIM switches back to NORMAL and attempted to trim up using their yoke switches. These inhibited MCAS commands as long as they were held in the Trim Up position. But, for whatever reason, it appears that the pilots only gave two short bursts of nose up trim, then released the switches. This allowed MCAS to kick in again with yet more nose down trim, which put the aircraft into an uncontrollable dive.

My understanding is that it would have been counter-intuitive for the pilots to reduce engine power while fighting to pull the nose up close to the ground, because the engine thrust vector provides a nose up pitching moment that would help counter the nose down moment from the stabiliser. It looks as though the autothrottle was engaged throughout the flight and did reduce thrust slightly when the speed reached VMO.

TheEdge · 30 Apr 2019

So Boeing are now trying to move the blame elsewhere. Meanwhile allegations claim that some safety equipment wasn't fitted or activated on the Southwests MAXs. And that whistleblowers had reported MCAS to regulators.

Boeing's boss has refused to admit that a system introduced in its 737 Max 8 aircraft was flawed following two fatal plane crashes.

Appearing in front of investors and the media, Dennis Muilenburg maintained the system was only one factor in a chain of events that led to the disasters.

But new reports have raised fresh questions about the plane's safety.

It has emerged that whistleblowers connected to Boeing contacted the US airline regulator about the system.

https://www.bbc.co.uk/news/business-47980959

ModernRailways · 30 Apr 2019

TheEdge said:
So Boeing are now trying to move the blame elsewhere. Meanwhile allegations claim that some safety equipment wasn't fitted or activated on the Southwests MAXs. And that whistleblowers had reported MCAS to regulators.

It would likely be even more damaging if they came out and said it was their fault. They are engaged in lawsuits over it and if they came out and said yes it was our fault then they are placing the blame entirely on their side. That would be devastating for Boeing. They likely know they're already partly to blame but coming out and saying it publically is a whole other thing. It's easier to wait for reports to come out into what has happened and then for them to go from there.

Peter Mugridge · 30 Apr 2019

I wonder if Mr Muilenburg would be willing to be on board when the first modified MAX takes off for the first time...?

AlterEgo · 3 May 2019

Peter Mugridge said:
I wonder if Mr Muilenburg would be willing to be on board when the first modified MAX takes off for the first time...?

Even the 737 MAX is safer than the taxi to the airport.

cactustwirly · 3 May 2019

AlterEgo said:
Even the 737 MAX is safer than the taxi to the airport.

Is it though? The 737s are clearly dangerous and they have a serious design flaw that makes crashing a lot more likely.
I'd rather take my chances with the Airport taxi, rather than a 737 Max.

YorkshireBear · 3 May 2019

I think it's the higher likelihood of a terrifying death that comes with the 737max rather than the actual risk of death for many I sense.

Bletchleyite · 3 May 2019

YorkshireBear said:
I think it's the higher likelihood of a terrifying death that comes with the 737max rather than the actual risk of death for many I sense.

The thing is, a car crash is probably survivable. Most plane crashes are also survivable, but the specific (and usually extremely rare) type the 737 MAX is prone to (falling out of the sky, basically) is not, and would be highly unpleasant as you'd know for a while beforehand that you were going to die. I don't fancy that, personally.

YorkshireBear · 3 May 2019

Bletchleyite said:
The thing is, a car crash is probably survivable. Most plane crashes are also survivable, but the specific (and usually extremely rare) type the 737 MAX is prone to (falling out of the sky, basically) is not, and would be highly unpleasant as you'd know for a while beforehand that you were going to die. I don't fancy that, personally.

Completely agree, you have made my point much better than I did.

Ethiopian Airways flight crashes (10/03) + 737 MAX grounding

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