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Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

reuters.com

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Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#191

Post by achandlerwhite »

pishpash wrote: post #34
dannyw wrote: post #17

Earlier quoted context omitted.

Because MCAS never assumes the input sensors could be faulty.

Sounds like a shitty and incompetent design. Grounding the plane was the right decision.

I agree, but I see the reasoning. MCAS failure leads to runaway trim for which there is an established and well known procedure to fix--in the checklist almost 50 years. For a problem with trim you flip the trim cutout switch. Doesn't matter if the problem stems from MCAS, autopilot, crossed wires, the magentic pole flipping, jammed electric motor, whatever.

It's like explaining to a computer user that rebooting will fix aproblem--they don't need to know the exact cause but just how to recover from it.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#192

Post by cjbprime »

achandlerwhite wrote: post #186
t0mas88 wrote: post #84

Earlier quoted context omitted.

The same applies to the trim in a 737 and any other transport class aircraft. If you move the control column in the opposite direction of trim, the electric trim and autopilot trim will cut out. The same applies to the autopilot in all types I've flown, it disconnects if you override it manually (except for CWS mode, but that's known and expected) I don't fly the 737, so I haven't read the aircraft specific books and…

Since MCAS and autopilot are two different things and MCAS is only active when autopilot is off I think it is faulty to assume that something that disables autopilot would disable MCAS--but in the heat of the moment I can see room for confusion.

The point in that the Lion Air pilots had no way to know of the very existence of MCAS, and therefore thought that the autopilot is the only system on the plane capable of issuing intentional trim changes, and therefore that disabling it would stop them.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#193

Post by dmix »

salawat wrote: post #167
bookofjoe wrote: post #55

Best book I've ever read on the root cause ("tight coupling") of accidents: https://en.wikipedia.org/wiki/Normal_Accidents From its Wikipedia entry: >"Normal Accidents: Living with High-Risk Technologies" is a 1984 book by Yale sociologist Charles Perrow, which provides a detailed analysis of complex systems from a sociological perspective. It was the first to "propose a framework for characterizing complex technolog…

See the post mortem of the THERAC-25 debacle. The consequences of reckless software interlocks and poorly trained operators has been known for a long time now.

The wiki for this incident: https://en.wikipedia.org/wiki/Therac-25

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#194

Post by achandlerwhite »

lawlessone wrote: post #71

>The manufacturer has said there is a documented procedure to handle the situation. A different crew on the same plane the evening before encountered the same problem but solved it after running through three checklists, according to the November report. They shouldn't have to do this routinely.

Agree, if the AoA sensor had been properly maintained and/or the MCAS was able to better handle a faulty sensor this could be mitigated.

Also pilots should be made aware of the characteristics of the resulting mode of stabilizer trim runaway.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#195

Post by achandlerwhite »

peteradio wrote: post #116

I'm becoming most curious about these AoA sensors. What is going on with them? Is there a problem in the manufacturing process?

I believe it was installed incorrectly and poorly maintained by the airline.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#196

Post by cjbprime »

wikibob wrote: post #36
neuronic wrote: post #32

Earlier quoted context omitted.

> In Boeing airplanes, the movement of the two yokes is synchronized. So in case of two equally strong and equally determined pilots you still get averaging of opposing control inputs.

No, the failure mode is not two pilots consciously fighting against each other. The failure mode is two pilots who are UNAWARE they are commanding contradicting inputs. Airbus negligently averages these inputs. This is legacy tech debt because the physical design didn’t leave room to link the two controls. Now they are stuck because they feel they can’t change and have some planes that (dangerously) average the input…

Or you could think of this: the A330 has fewer total fatalities than the MAX, despite being in service for over 25 years instead of under 2 years.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#197

Post by lsh123 »

_s wrote: post #177
zaroth wrote: post #150

The previous flight had exactly the same issue. This is what that pilot wrote in the logs; After parking, the PIC informed the engineer about the aircraft problem and entered IAS (Indicated Air Speed) and ALT (altitude) Disagree and FEEL DIFF PRESS (Feel Differential Pressure) light problem on the Aircraft Flight Maintenance Log (AFML). The PIC also reported the flight condition through the electronic reporting syste…

It probably is a memory item, but it's not something they got to immediately, and I'm guessing here because runaway trim symptoms are slightly different to what MCAS was doing. This happened to me a while ago involving trim, and I'll try and go through my thought process and why it takes a little while in the cockpit to figure things out: - Autopilot is engaged, holding a heading of X, altitude of Y and I've got a po…

I had an autopilot/trim issues once on the approach right after FAF in solid IMC (later turned out that one of wires got loose). Similar symptoms as above. I didn’t debug anything, simply killed AP, and hand flew the rest of the approach. It was exactly the response my instrument instructor trained me to do and he was very happy when I discussed it with later.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#198

Post by petilon »

achandlerwhite wrote: post #189
petilon wrote: post #185

Earlier quoted context omitted.

So in other words they designed it this way in order to make the 737 MAX is cheaper to operate, and therefore easier to sell. That's terrible. Boeing traded off safety for profits.

Yes cost is a factor. The alternative might not be feasible economically. I don't think the failure here was reusing the 737 design, but the downstream due diligence of implying no significant changes. I also think airline training is a factor--both Boeing for the new systems and the airliners because runaway stabilizer trim has been in the aircraft emergency checklist for over 50 years and every pilot should know it…

Sacrificing safety in order to reduce cost is unjustifiable. When you design a multi-layer system, the higher layers should be for enhanced functionalities, not for fixing flaws in lower layers. Boeing designed flawed hardware (yes, it was intentional but that doesn't mean it is not a flaw) and tried to fix the flaw in software.

Then Boeing supplied a flight manual that a pilot described as 'inadequate and almost criminally insufficient', in order to convince customers that moving from older 737s to the MAX does not require extensive retraining. All in all, there is ample evidence that Boeing put profits above safety.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#199

Post by js2 »

Someone1234 wrote: post #165
zaroth wrote: post #150

The previous flight had exactly the same issue. This is what that pilot wrote in the logs; After parking, the PIC informed the engineer about the aircraft problem and entered IAS (Indicated Air Speed) and ALT (altitude) Disagree and FEEL DIFF PRESS (Feel Differential Pressure) light problem on the Aircraft Flight Maintenance Log (AFML). The PIC also reported the flight condition through the electronic reporting syste…

MCAS problems weren't a memory item for any pilot, the memory item is Runaway Stabilizer and exhibits different behaviour to MCAS. Which is to say that they'll be receiving sim training for Runaway Stabilizer, learn what to expect (wheel moves continuously, hard nose down, etc), and then in real life have MCAS cause the same issue but in a substantively different way (change, delay, change, delay, etc). Without the b…

I agree it is a training problem, but it also seems the case that some pilots understand the fundamentals of flight and how a plane operates than others. So when a plane misbehaves, some pilots may have an intuitive sense of what to do, while others are stuck pattern matching and running through checklists.

To make a terrible analogy that trivializes the complexity of flying a jet (because I can't think of a better one), it's like the difference between a chef who knows how to combine ingredients to get the desired result and a cook who only knows how to follow a recipe.

Re: Cockpit voice recorder of Lion Air jet depicts pilots' frantic search for fix

#200

Post by js2 »

_s wrote: post #188
js2 wrote: post #183

Earlier quoted context omitted.

Thank you for a pilot's perspective. Here's my bit of confusion though. Once you realized the stab trim was the issue, you were able to reset it and get back to normal flight. Had the problem recurred that flight, you'd probably have recognized it immediately. In the Lion flight, the pilots realize the stab trim is off because they correct it. Once they realize that, regardless of what keeps setting the stab trim to…

I think context is what helps - - I’ve just taken off, and am going through the after take off checklist: Set the airspeed, power, climb rate, heading, talking to ATC, planning the next stage of the flight - Perhaps I’ve just raised the flaps and the plane starts behaving erratically - My first / immediate thought is that my previous action led to an undesired aircraft state. - I work from that point on - I touch the…

I think that, not being a pilot, I can't really understand, but thank you again for the perspective.

Edit: one last thing though - when the plane isn’t behaving as expected, why isn’t the first thing to check that all the control surfaces and the throttle are where you expect them to be?

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