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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

#31

Post by acqq »

Someone1234 wrote: post #14
frenchy wrote: post #9

Earlier quoted context omitted.

I doubt it would have been "out of control", it would have just been slow changes over time as trim increased. The pilots might not have been fighting it much either, if they thought that airspeed was the problem, and not pitch.

The graph on page 14 of this report[0] is pretty telling about how slow the changes were... Note Trim Manual, Trim Automatic, and Pitch Trim Position. [0] https://reports.aviation-safety.net/2018/20181029-0_B38M_PK-...

Thanks! Page 23 of the PDF or 14 as printed at the bottom. Sadly it's hard to compare with the previous flight (pg. 25 or 16) as for it they published the graph of the whole flight instead of only the part until the (at the time still secret) MCAS was turned off (or probably more correctly, the motor controlled by the MCAS, which actually steered the "trim").

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

#32

Post by neuronic »

piquadrat wrote: post #27
StreamBright wrote: post #20

Earlier quoted context omitted.

Flight augmentation systems work a different way. Those take into consideration all inputs and average it out. Same when two pilots give different instructions.

> Same when two pilots give different instructions. That's only true for Airbus (and probably contributed to the loss of Air France 447, https://en.wikipedia.org/wiki/Air_France_Flight_447 ). In Boeing airplanes, the movement of the two yokes is synchronized.

> 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.

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

#33

Post by losvedir »

dukoid wrote: post #30
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.

To my understanding, the trim wheels are moving frequently for small adjustments -- and it's possible to switch the wheel movement off if this becomes too annoying.

Also not a pilot but I don't think you can switch the wheel off. You can, however, disable the electric motors that spin the wheel, which is what the checklist for runaway trim tells you to do, and what was supposed to have been done here.

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

#34

Post by pishpash »

dannyw wrote: post #17
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).

Because MCAS never assumes the input sensors could be faulty.

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

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

#35

Post by acqq »

gojomo wrote: post #7
jve wrote: post #4

In the other news, on the previous day on the same plane there was a retired pilot flying in cockpit who correctly diagnosed problem & told how to disable malfunctioning system: https://www.bloomberg.com/news/articles/2019-03-19/how-an-ex...

That's the most amazing revelation to me so far. The same plane had an identical uncontrolled-dive problem the day before, which required an emergency power cut to the improperly-engaged motor, and somehow that incident didn't ground the plane or even result in any effective advisory to the next crew. Further, the Bloomberg story reports: "The Indonesia safety committee report said the plane had had multiple failures…

> 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 observers to recognize that just blaming the pilot or maintenance won't keep the planes from not crashing.

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

#36

Post by wikibob »

neuronic wrote: post #32
piquadrat wrote: post #27

Earlier quoted context omitted.

> Same when two pilots give different instructions. That's only true for Airbus (and probably contributed to the loss of Air France 447, https://en.wikipedia.org/wiki/Air_France_Flight_447 ). In Boeing airplanes, the movement of the two yokes is synchronized.

> 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 inputs, and some that are physically linked.

When controls are physically linked, if one pilot thinks he should nose up, and the other tries to nose down, they can yell “what are you doing” at each other and this create an accurate mental model of what the other is intending.

Think of this every time you fly Airbus.

It’s very similar to debugging a production technology issue. Imagine you decide to restore the database to a snapshot from 1 hour ago, and at the same time someone else tries to restore to an earlier snapshot from 12 hours ago.

Should the system average these inputs and restore from 6.5 hours ago? No, obviously not.

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

#37

Post by Tepix »

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.

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

#38

Post by kissickas »

neuronic wrote: post #32
piquadrat wrote: post #27

Earlier quoted context omitted.

> Same when two pilots give different instructions. That's only true for Airbus (and probably contributed to the loss of Air France 447, https://en.wikipedia.org/wiki/Air_France_Flight_447 ). In Boeing airplanes, the movement of the two yokes is synchronized.

> 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.

It sounds far more intuitive if you have a feedback mechanism in the form of a tangible demonstration of what the force is actually averaging out to.

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

#39

Post by cyberferret »

gojomo wrote: post #7
jve wrote: post #4

In the other news, on the previous day on the same plane there was a retired pilot flying in cockpit who correctly diagnosed problem & told how to disable malfunctioning system: https://www.bloomberg.com/news/articles/2019-03-19/how-an-ex...

That's the most amazing revelation to me so far. The same plane had an identical uncontrolled-dive problem the day before, which required an emergency power cut to the improperly-engaged motor, and somehow that incident didn't ground the plane or even result in any effective advisory to the next crew. Further, the Bloomberg story reports: "The Indonesia safety committee report said the plane had had multiple failures…

Or at the very least, entered into the aircraft maintenance log. Back in my flying days, we had to enter every issue, large or small, into the aircraft maintenance logbook, and we also had to check it before each new flight to see what other crews had experienced, and whether the fault was signed off as 'fixed' or an 'up' fault that we could take into the air with us on the next flight.

I believe the tighter turnaround times of flights these day may either mean this step is rushed too quickly or omitted altogether...

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

#40

Post by TheSpiceIsLife »

ahoka wrote: post #25
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.

If anyone wonders this is how it looks like: https://youtu.be/-X01uY0bJs0?t=48

And sounds?

The trim wheels moving also makes a sound?

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