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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

#211

Post by bdamm »

jcims wrote: post #208
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…

Are the logs you're referencing a public resource? Would be interesting to look at. >This implies it took almost three minutes for the previous crew to figure out the STAB TRIM needed to be CUT OUT after finding the trim is so wrong that they can’t hold the stick back. I've seen a number of references to difficulty that pilots encounter managing forces of the flight controls in airliners. It seems strange to me that…

The scaled assistance you're referring to is the hydraulic system.

Airplanes are supposed to be light-touch because you need very fine movement control to balance the aircraft while landing. Think of the work required to move a pencil. That's about the level of effort a plane is supposed to require. But with the trim working against the pilot, the control required could be more like lifting a 50lb sack.

Yes, most pilots can lift a 50lb sack. Can you lift and hold a 50lb sack for, say, an hour? Not many people can.

(Without hydraulics, the forces would simply toss the pilot's body around. No possibility of control.)

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

#212

Post by kevin_thibedeau »

_archon_ wrote: post #123
dannyw wrote: post #17

Earlier quoted context omitted.

Because MCAS never assumes the input sensors could be faulty.

It's worse than this. MCAS is designed to only look at one of the two AoA sensors. If this happens to be faulty, it doesn't know, because it's not comparing the sensor to the other one. Instead of a system which can notice and account for disagreeing sensors and fail gracefully, we have a system which is a designed single point of failure and fails... lethally.

You can't handle faults with only two sensors since you won't know which one to trust. At least three would be needed for a minimal level of redundancy.

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

#213

Post by foldr »

livatlantis wrote: post #205
jandrese wrote: post #174

Earlier quoted context omitted.

Did AF447 not have this warning? One of the contributing factors to the crash was the copilot continuing to pull back on the stick even as the pilot attempted to push the nose down to get out of the stall.

I answered further up but: yes, it did. The DUAL INPUT alarms were audible in the cockpit voice recording. However, unbeknowst to the captain, the co-pilot used priority takeover on his side. (This was always visible on the panel + there was an audible "Priority right" warning around the end) Source: https://www.vanityfair.fr/actualites/articles/vol-af-447-rio...

I'm not sure where you're getting the "unbeknownst" from. In the cockpit voice recorder transcripts attached to the official accident reports, it seems that the pilots were aware of who had control at any given point in time.

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

#214

Post by foldr »

_archon_ wrote: post #120
LoSboccacc wrote: post #99

Earlier quoted context omitted.

> why it would continue to drive the nose of the plane down even when the pilot is reefing on the stick to pull up well this other crash was caused by a pilot puling up a plane all the way to its ceiling and stalling it, so there's that, so things can go wrong whether if you do and if you don't allow for easy control overrides. https://en.wikipedia.org/wiki/Air_France_Flight_447#Third_in... the trick seems to find th…

The AF 447 crash is one of the reasons MCAS was created. It's the exact scenario MCAS was designed to prevent: High altitude, high-speed, nose-up stall. This was more likely than the NG and dinosaur generations of 737 due to the engine relocation forward and up (causing a pitch-up moment due to thrust). AF 447 should never have happened. The copilot crashed the plane, and the pilot and pilot on break had no indicatio…

>There was no feedback, and the controls deferred to his inputs when the pilot was trying the opposite command (which would have saved the flight).

I've never seen a reliable source for the claim that the two pilots at the controls were pushing the stick in opposite directions for any extended period of time. What's the primary source for this info?

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

#215

Post by VBprogrammer »

bdamm wrote: post #211
jcims wrote: post #208

Earlier quoted context omitted.

Are the logs you're referencing a public resource? Would be interesting to look at. >This implies it took almost three minutes for the previous crew to figure out the STAB TRIM needed to be CUT OUT after finding the trim is so wrong that they can’t hold the stick back. I've seen a number of references to difficulty that pilots encounter managing forces of the flight controls in airliners. It seems strange to me that…

The scaled assistance you're referring to is the hydraulic system. Airplanes are supposed to be light-touch because you need very fine movement control to balance the aircraft while landing. Think of the work required to move a pencil. That's about the level of effort a plane is supposed to require. But with the trim working against the pilot, the control required could be more like lifting a 50lb sack. Yes, most pil…

Also worth noting that the reason we don't simply scale the forces down to the point a pilot could easily handle them is that above manouvering speed an aircraft can be damaged by full control deflection.

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

#216

Post by kayfox »

acqq wrote: post #11
cjbprime wrote: post #6

Earlier quoted context omitted.

The spin was not visible to these pilots presumably because it was happening in small increments with a delay between them.

Exactly. It was not "runaway" in the sense of "continuously doing the same." Something was happening, from the point of view of the pilot and co-pilot "at random." (Not to mention that on the previous models exactly such pattern was effectively impossible to happen). The faulty non-redundant sensor was producing false reading and that was the input to the to the pilots completely unknown MCAS which then moved the nos…

"Runaway" in the sense of "its moving in a undesired and unexpected direction and continues to do so despite attempts to stop it".

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

#217

Post by iron0013 »

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…

I can see how a single instance of a particular accident type might be unavoidable, but every subsequent accident attributable to the same cause(s) is absolutely avoidable.

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

#218

Post by Someone1234 »

sgc wrote: post #210
Someone1234 wrote: post #171

Earlier quoted context omitted.

Maintenance attempted a repair between those two flights. They flushed the AoA system after replacing it previously.

They should have given the incoming pilots a thorough briefing of: this is what went wrong, this is how the previous pilots worked around it, this is what we did to remedy.

That's what this comment chain is about, the log book. Maintenance would have added comments after the previous pilot's above.

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

#219

Post by jandrese »

foldr wrote: post #213
livatlantis wrote: post #205

Earlier quoted context omitted.

I answered further up but: yes, it did. The DUAL INPUT alarms were audible in the cockpit voice recording. However, unbeknowst to the captain, the co-pilot used priority takeover on his side. (This was always visible on the panel + there was an audible "Priority right" warning around the end) Source: https://www.vanityfair.fr/actualites/articles/vol-af-447-rio...

I'm not sure where you're getting the "unbeknownst" from. In the cockpit voice recorder transcripts attached to the official accident reports, it seems that the pilots were aware of who had control at any given point in time.

I remember right before the impact with the water the captain finally realizing why his controls aren't doing anything and asking the co-pilot to finally let go of his stick. IIRC they never did throttle up however. Ultimately the co-pilot got tunnel vision and thought for some reason they were in an overspeed condition for most of the incident and failed to communicate that effectively with the rest of the crew. He made a couple of comments about it, but nobody else realized that he was attempting to correct for an overspeed condition in the middle of a dead stall, even when the airspeed indicator came back it seemed wrong to him because he thought they were going too fast.

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

#220

Post by __turbobrew__ »

kevin_thibedeau wrote: post #212
_archon_ wrote: post #123

Earlier quoted context omitted.

It's worse than this. MCAS is designed to only look at one of the two AoA sensors. If this happens to be faulty, it doesn't know, because it's not comparing the sensor to the other one. Instead of a system which can notice and account for disagreeing sensors and fail gracefully, we have a system which is a designed single point of failure and fails... lethally.

You can't handle faults with only two sensors since you won't know which one to trust. At least three would be needed for a minimal level of redundancy.

You can handle faults by disabling the MCAS system which is a lot better than the current solution of diving the nose into the ground.
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