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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

#61

Post by foldr »

philpem wrote: post #43
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.

If they're mechanically linked, the captain would at least feel the first officer countering their inputs -- giving a prompt that they need to communicate their intentions more clearly! I'll defer to a pilot to say whether they are mechanically linked -- it sounds like they are on Boeing aircraft but possibly not on Airbus?

No, the captain would not, because only one pilot has their hands on the controls in any given instance (with the possible exception of rotation at takeoff).

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

#62

Post by verytrivial »

RidingPegasus wrote: post #3
cjbprime wrote: post #2

This appears to answer the question of why, given that there is a "memory item" for dealing with runaway trim that would have helped, it wasn't followed by the crew: > “They didn’t seem to know the trim was moving down,” the third source said. “They thought only about airspeed and altitude. That was the only thing they talked about.” If this is true, not only did the pilots not realize the trim was the cause of the d…

Was the trim wheel not visibly spinning out of their control? Simply because the symptoms are different should mean that stopping it via taking manual control is a recurring option.

The Lion Air directive has instructions on page 41 of their preliminary report that include:

5. If the runaway continues after the autopilot is disengaged:

   STAB TRIM CUTOUT switches (both)  ... CUTOUT
   If the runaway continues:
      Stabilizer trim wheel  .... *Grasp and hold*
This may be an overabundance of caution, or to cover other runaway events, but it reads like "you may need to physically fight the computer even when it has been disabled". Not exactly heartening.

EDIT: A comment below points out haptic feedback to disengage as a reason to grab-and-hold.

https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...

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

#63

Post by sean-duffy »

programmer_dude wrote: post #15

What I don't understand whenever I read anything related to the MCAS system is why does it not check if the plane is in a dangerous nose dive using other sensors the plane might have? Does the average plane not have a gyroscope? My sub 500 dollar phone has both a gyroscope and an inertial measurement unit (accelerometer).

Probably because entering a "dangerous nose dive" is the correct way to avoid an impending stall, which is what MCAS is supposed to do.

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

#64

Post by oasisbob »

crooked-v wrote: post #12
RidingPegasus wrote: post #3

Earlier quoted context omitted.

Was the trim wheel not visibly spinning out of their control? Simply because the symptoms are different should mean that stopping it via taking manual control is a recurring option.

Part of the problem is that the MCAS system has a 20-second delay after the last time the pilot touched controls for the flaps, and it adjusts itself to a new position and then stops. There are no other indicators that it's happening, and since it's noncontinuous and has a delay, it would be easy to miss the only visual sign of the trim wheel readjusting itself once, especially since the wheel itself is by the pilot'…

I'm not sure that's accurate. Other descriptions of the MCAS system state that it will continually modify the trim on the horizontal stabilizer for up to 10 seconds at a time.

http://www.b737.org.uk/mcas.htm

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

#65

Post by mjburgess »

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 think this perspective on accidents needs far more emphasis.

Many accidents are unavoidable and not the result of some person failing to do some thing.

The world isn't a story, people don't have much agency, and events do not happen because people want them to.

These "narrative explanations" are mythological just-so stories that attribute the complex interaction of systems to individuals, organizations, etc. in naive agency-based ways.

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

#66

Post by acqq »

icebraining wrote: post #56
acqq wrote: post #35

Earlier quoted context omitted.

> Lots of blame to go around here. Only if the faulty sensor was listed as "critical." Boeing didn't declare it as such and reported to nobody the way it was used in the unreported MCAS. That the MCAS even exists and that a single faulty sensor was enough to mess with the flight erratically enough to confuse the pilots was somehow acknowledged by Boeing only after the first crash. It took the second crash for most ob…

Even if they didn't know about the MCAS, they still knew the plane had had an uncontrolled-dive problem from an unknown cause. How is it responsible to fly it without understanding the issue? Boeing is still fully culpable, but the airline should have debugged the issue before using the plane again.

> How is it responsible to fly it without understanding the issue?

There is not only "the issue" there are a lot of "issues" happening all the time. The problem is even knowing which are "too serious." That the single faulty sensor which didn't affect anything on the previous planes could mean the difference between the life and death was specifically not reported by Boeing.

How it is responsible to certify the plane without properly analyzing the MCAS implementation?

https://www.nytimes.com/2019/03/19/business/boeing-elaine-ch...

And how it is responsible to claim "everything is OK everywhere" after the two crashes?

https://www.barrons.com/articles/faa-not-grounding-boeing-73...

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

#67

Post by rusk »

mjburgess wrote: post #65
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 think this perspective on accidents needs far more emphasis. Many accidents are unavoidable and not the result of some person failing to do some thing. The world isn't a story, people don't have much agency, and events do not happen because people want them to. These "narrative explanations" are mythological just-so stories that attribute the complex interaction of systems to individuals, organizations, etc. in nai…

Yes, but, its no excuse for relaxing operational rigor. Those who fail to learn from history are doomed to repeat it. And if you repeatedly ignore the lessons of experience then you are to blame.

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

#68

Post by ethelward »

Tepix wrote: post #37
programmer_dude wrote: post #15

What I don't understand whenever I read anything related to the MCAS system is why does it not check if the plane is in a dangerous nose dive using other sensors the plane might have? Does the average plane not have a gyroscope? My sub 500 dollar phone has both a gyroscope and an inertial measurement unit (accelerometer).

Gyroscopes by themselves can not sense the orientation of a body moving through three dimensions.

What is that[0] then?

https://en.wikipedia.org/wiki/Attitude_indicator

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

#69

Post by inferiorhuman »

oasisbob wrote: post #64
crooked-v wrote: post #12

Earlier quoted context omitted.

Part of the problem is that the MCAS system has a 20-second delay after the last time the pilot touched controls for the flaps, and it adjusts itself to a new position and then stops. There are no other indicators that it's happening, and since it's noncontinuous and has a delay, it would be easy to miss the only visual sign of the trim wheel readjusting itself once, especially since the wheel itself is by the pilot'…

I'm not sure that's accurate. Other descriptions of the MCAS system state that it will continually modify the trim on the horizontal stabilizer for up to 10 seconds at a time. http://www.b737.org.uk/mcas.htm

To summarise; MCAS will trim the Stabilizer down for 10 seconds (2.5 deg nose down) and pause for 5 seconds and repeat if the conditions (high angle of attack, flaps up and autopilot disengaged) continue to be met. Using electric pitch trim will only pause MCAS, to deactivate it you need to switch off the STAB TRIM SUTOUT switches.
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