Ethiopian airliner down in Africa

[FGD135]

calypso,

I think yours is a very good summation. I was just looking closely at the JT610 FDR data last night. The big difference between the Lionair accident flight and the previous flight was that the previous crew immediately disabled the electric stab trim.

[DaveReidUK]

Originally Posted by indigopete

A stick pusher is an emergency recovery system that basically assumes the pilot is effectively "dead" (or at least their brain is). Not dissimilar to a dead man's handle on a train in some limited respects. It's on all/most airliners regardless of their design and is independent of the manoeuvring characteristics of the particular type.

Do you mean a stick-pusher? Or a stick-shaker? They are two different things.

Incidentally, a poster earlier asked about the manufacturer of the 737 NG/Max AoA probe. I don't recall the question being answered.

Like the probes on many commercial airliners (not just Boeings), it's made by Rosemount, later part of Goodrich, subsequently absorbed into Collins Aerospace and nowadays part of United Technologies. So you are likely to see any of those names quoted as the manufacturer, depending on chronology.

[MemberBerry]

Originally Posted by FGD135

calypso,

I think yours is a very good summation. I was just looking closely at the JT610 FDR data last night. The big difference between the Lionair accident flight and the previous flight was that the previous crew immediately disabled the electric stab trim.

You should look again at that Lion Air FDR data. It clearly shows the pilots of the previous flight NOT immediately disabling electric trim, and instead fighting MCAS for at least 4 minutes before disabling it. On the time axis each grid unit has 11 minutes, and the fight with MCAS is represented over almost half a grid unit.

[Sublogic]

AoA sensors

The AoA sensor as such may deserve a closer look. First, it is difficult to google their physics and history in the first place. There is a NASA report from 2014 summarizing the historical development. Seems that these type of sensors are relatively new outside military planes. Feeding its output into automated systems may not be straight forward: “Sensor Fault” may come in many shades. As a good sensor, it certainly has DC voltage lines monitoring and AD well-being indicators and possibly an automated test signal insert with check functions. So the case of using several sensors, like in a Sub-Prime bond bundle, versus the good caring of one deserves attention.

With all this considered, it seems difficult to judge a system that takes a non-monitored output from one complicated sensor to drive a control loop.

[Dave Ed]

All very similar to the A400M crash in 2015.

https://www.reuters.com/article/us-a...-idUSKBN1D819P

I am CAA licenced engineer working on "clockwork" Bell 412 helicopters at present. When we disturb any part of the flight control and/or engine control systems, we carry out independent duplicate inspections. With these software driven aircraft, how are software changes to flight control / engine management systems certified after changes made. Do they require similar duplicate independent inspections? and by who?

[derjodel]

Originally Posted by Livesinafield

Guys, think people need to ease of the aircraft a little as if its got some huge design defect especially until we have some more facts, bear in mind many operators have been using this type for a fair while southwest nearly 3 years, with no such issues, also bear in mind that both operators here that have managed to "fly it into the ground" have very questionalble safety records as an operator.

Right, ET also managed to put 787 on fire while there were others flying about without an issue. Sheer incompetency!

Seriously, what is the data which leads to "questionable safety record" conclusion ET? And please adjust for hijackings, unless you are going to claim somehow those are also ET's fault.

In reality, if you take out the recent MAX crash and the 96 hijacking, they have about 200 fatalities since 1948. Questionable safety!?

[Piper J3]

Reuters Business News headline on my homepage - "Boeing 737 MAX software patch expected before end-March". Calling the proposed solution, a “software patch” isn’t going to enamor the flying public.

[Kerosene]

Originally Posted by FCeng84

MCAS is able to do its job with 2.5 degrees of stabilizer up to Mach 0.4 and less than 1/3rd of that at cruise. That MCAS can insert more stabilizer motion that this design limit is beyond its design requirements. There is not a control power deficiency as there is plenty of elevator to counter the design levels of stabilizer that MCAS needs.

This suggests a future MCAS software update will limit stabilizer motion to benign values sufficient to achieve design requirements, therefore excluding a scenario where MCAS could become the cause of inadvertent full stabilizer down trim. So far, so good.

However, I can't help wondering about this: if a system like MCAS is required to demonstrate flight handling characteristics in conformity with certification requirements throughout the flight envelope, without which the aircraft could not have been certified, how are those being met in the absence of MCAS after an in-flight event (following a reversion to manual trim due to e.g. erroneous activation or stabilizer trim malfunction)? Excuse the crude analogy, but this seems to compare with a normally aerodynamically sound and certified aircraft inadvertently losing a part of its structure, therefore not necessarily rendering it unflyable, but certainly outside its certified state into an emergency situation.

I'm surprised the aircraft was allowed to reach certification with this known possibility (to extend the analogy, accepting the likeliness of losing some part of the airframe in flight). Furthermore without mandating simulator training for dealing with the more unfavorable handling characteristics in approach to stall scenarios without MCAS (not even speaking of telling the flight crews about the system in the first place or training them for MCAS having under certain conditions authority to trim the stabilizer full nose down on a single sensor input - unthinkable!).

[pilotmike]

Originally Posted by canyonblue737

the fix has been in development for 5 months and was due now anyway, they aren't starting from scratch.

Not really. That was then. This is now.

They WERE working on a fix to what was hoped to be a very minor issue with an almost secret system, that they hoped nobody really knew about. And it was probably going to get about the same level of attention to detail and safety and testing that the original 'almost ok' system it was fixing - ie. just get it done and into service as quickly and cheaply as possible, without too much fuss.

Now, however, the task is somewhat bigger. It is a fix for a badly broken system which is unfit for purpose, which by all accounts has directly killed hundreds of innocent passengers and crew. Not only that, but it is being done under the scrutiny of the whole world, where EVERYBODY knows about it, and pretty much the whole World has lost faith in Boeing to do it properly. The FAA and all the other countries of the World's Regulatory bodies will be fully aware that the travelling public are unlikely ever to fully trust this, so the standards against which it will be judged will have to be set very high.

So I don't think we can expect the fix to be "due now", based on it having "been in development for 5 months". The task is far bigger than they hoped.

[infrequentflyer789]

Originally Posted by FGD135

FCeng84, are you saying the stab cutout switches won't stop the MCAS from acting?

FCeng84 was referring to the column cutout switches, which MCAS does override (it will trim nose down even when pilot is pulling up - unlike speed trim). The cutout switches on the throttle quadrant will (if working as designed) stop MCAS.

It seems that everybody here wants to bash Boeing for not training pilots at how to deal with the MCAS inadvertent activation. But Boeing have provided training and guidance. The problem is that this guidance wasn't followed by the Lion Air crew

Umm, Boeing didn't provide pilots with any information on MCAS until after Lion Air crashed, pilots were not supposed to need to know about it.

A large part of the problem is that Boeing wants the MAX to be just another NG (for commercial reasons) - MAX pilots can fly it without any MAX sim time (because there aren't many commercial MAX sims, and it isn't known if any of the have MCAS), the only training is apparently a powerpoint. Try "fixing" the problem by mandating an MCAS sim exercise for all MAX pilots and see how far you get - my prediction is the Boeing will fight it tooth and nail.

To repeat, the MAX is just another NG, it's just that with the same pilots same airlines same everything else, the MAX is a bit crashier...

[oldchina]

Originally Posted by indigopete

A stick pusher is an emergency recovery system that basically assumes the pilot is effectively "dead" (or at least their brain is). Not dissimilar to a dead man's handle on a train in some limited respects. It's on all/most airliners regardless of their design and is independent of the manoeuvring characteristics of the particular type.

Well not quite.
It's on around two thirds of all airliners. The rest are A318s, 319s, 320s, 321s, 330s, 340s, 350s and 380s

[Ian W]

Originally Posted by fdr

§ 25.672 Stability augmentation and automatic and power-operated systems

If the functioning of stability augmentation or other automatic or power-operated systems is necessary to show compliance with the flight characteristics requirements of this part, such systems must comply with § 25.671 and the following:

(a) A warning which is clearly distinguishable to the pilot under expected flight conditions without requiring his attention must be provided for any failure in the stability augmentation system or in any other automatic or power-operated system which could result in an unsafe condition if the pilot were not aware of the failure. Warning systems must not activate the control systems.

(b) The design of the stability augmentation system or of any other automatic or power-operated system must permit initial counteraction of failures of the type specified in § 25.671(c) without requiring exceptional pilot skill or strength, by either the deactivation of the system, or a failed portion thereof, or by overriding the failure by movement of the flight controls in the normal sense.

(c) It must be shown that after any single failure of the stability augmentation system or any other automatic or power-operated system -

(1) The airplane is safely controllable when the failure or malfunction occurs at any speed or altitude within the approved operating limitations that is critical for the type of failure being considered;

(2) The controllability and maneuverability requirements of this part are met within a practical operational flight envelope (for example, speed, altitude, normal acceleration, and airplaneconfigurations) which is described in the Airplane Flight Manual; and

(3) The trim, stability, and stall characteristics are not impaired below a level needed to permit continued safe flight and landing.

[Amdt. 25-23, [url=https://www.law.cornell.edu/rio/citation/35_FR_5675]35 FR 5675 Apr. 8, 1970]

It all depends whether you believe the AOA vanes and system are part of the MCAS. Its like using an ASI display spec to regulate the pitot/static systems. MCAS worked precisely as it should - it was given the incorrect inputs. Inputs that were also used for ADIRUs and those systems provided a cacophony of warnings - for some reason their logic does not include an AOA disagree and that warning light is an 'optional extra'.

As was stated repeatedly on the AF447 thread AOA should be considered a non-optional display and AOA disagree should also be non-optional. An AOA disagree should result in the disabling of any system would operate dangerously. However, as was stated up thread a lot more logic could be used to identify and isolate the incorrect AOA. Only validated AOA information should be fed to systems or those systems disabled.

[FGD135]

Umm, Boeing didn't provide pilots with any information on MCAS until after Lion Air crashed, pilots were not supposed to need to know about it.

I can see what Boeing were trying to do. From their point of view, the pilots are already trained (supposedly) to deal with the situation the MCAS may bring up, so why complicate things?

If the pilots had followed the prescribed procedure for inadvertent/inappropriate/runaway stabiliser trim (a procedure which has existed for decades, across all Boeing models) then these crashes would not have occurred and the pilots would be none the wiser about MCAS.

[edmundronald]

ET302 Stab jackscrew found , trimmed to dive

The smoking gun implicating MCAS ie. the stabiliser jackscrew has been found.

https://www.ndtv.com/world-news/piec...o-dive-2008100

In the light of physical evidence which is hard to suppress, I think we can now expect some resignations at the FAA, and a hard look at the airplane’s other possible failure modes. I don’t think the 737 Max-8 will get ungrounded as easily as it got certified the first time round.

Edmund

[deltafox44]

Originally Posted by FCeng84

MCAS is able to do its job with 2.5 degrees of stabilizer up to Mach 0.4 and less than 1/3rd of that at cruise. That MCAS can insert more stabilizer motion that this design limit is beyond its design requirements. There is not a control power deficiency as there is plenty of elevator to counter the design levels of stabilizer that MCAS needs.

There is plenty of elevator to counter MCAS, but has the pilot enough strength to pull the control column to do so, even when speed increases to 380 kts, given that the artificial feel increases with speed ?

It seems the only chance not to crash, if manual trimming was not possible due to elevator up forces, would have been reducing power, airbrakes out, to cut the speed, then flaps down to kill MCAS and use electric trim again...

[derjodel]

Originally Posted by deltafox44

So... it seems that Boeing confirms this procedure that I had taken for a joke : before trimming, push the stick forward :

Push forward for 2-3 seconds while 2000 AGL@300 knots...

[DaveReidUK]

Originally Posted by edmundronald

In the light of physical evidence which is hard to suppress, I think we can now expect some resignations at the FAA

You're probably right.

But what's really needed is an in-depth look at the (changed) relationship between the regulators and the industry (by no means confined to the USA).

[Rated De]

Originally Posted by DaveReidUK

You're probably right.

But what's really needed is an in-depth look at the (changed) relationship between the regulators and the industry (by no means confined to the USA).

Regulatory Capture.

Partnerships with regulators.
Steak dinners, self regulation.
Soft corruption abounds.

Revolving doors between the regulator and industry. Just look at Aii Barhrami

As Charlie Munger says, Show me the incentive, I show you the outcome.

[Smdts]

Originally Posted by deltafox44

So... it seems that Boeing confirms this procedure that I had taken for a joke : before trimming, push the stick forward :

That looks like they are admitting the jackscrew can be prone to binding right at the time when you can least afford it to, when it has an extreme load on it in the wrong direction.
Is it possible once the loads were too great the jackscrew locked up and they never had time/realisation to unload it enough to free it?
Non pilot here, studying for ppl though and very interested in electromechanical engineering.

[edmundronald]

Jackscrew found
https://www.ndtv.com/world-news/piec...o-dive-2008100

Edmund