Ethiopian Airlines plane crashes on way to Nairobi

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CarlGrobler58
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by CarlGrobler58 » Fri Oct 18, 2019 8:48 am

So this system will override the pilot's uptrim being held on the yoke. So while you are trimming up the system trims down?
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by richard C » Fri Oct 18, 2019 9:25 am

CarlGrobler58 wrote:
Fri Oct 18, 2019 8:48 am
So this system will override the pilot's uptrim being held on the yoke. So while you are trimming up the system trims down?
That is the sole purpose of the system -

- to continuously feed in nose-down pitch to prevent a stall, irrespective of the pilots actions, this state being determined by a single AOA sensor that had in both cases, failed.

So I go back to my precis of Sully's take on this:
It's not the pilots job to decode a complex fault on the hoof - he expects to be given a reliable and predictable machine to operate, whose reliability and predictability has been certified by a trustworthy authority.
In this case the system was neither reliable nor predictable, and apparently not certified by a 'trustworthy' authority.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by jimdavis » Fri Oct 18, 2019 9:52 am

richard C wrote:
Fri Oct 18, 2019 9:25 am
So I go back to my precis of Sully's take on this:
It's not the pilots job to decode a complex fault on the hoof - he expects to be given a reliable and predictable machine to operate, whose reliability and predictability has been certified by a trustworthy authority.
In this case the system was neither reliable nor predictable, and apparently not certified by a 'trustworthy' authority.
I hear you loud and clear Christopher, but anyone can handle reliable and predictable - our job is to handle things when they stop being reliable and predictable.

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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by richard C » Fri Oct 18, 2019 10:03 am

Fair enough - but I think that responsibility stops short of an aircraft that seems intent on flying itself into the ground !!

Thanks for the new moniker, Jim - I like it !
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by heisan » Fri Oct 18, 2019 10:08 am

richard C wrote:
Fri Oct 18, 2019 8:25 am
"Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT."

That is what they did. What the instruction does not seem to take cognizance of is what if the MCAS has already lowered the nose significantly whilst very close to the ground. If you have resorted to the electric trim to try and rectify this, should your action take more than 5 seconds to sort itself out, the MCAS is going to start spooling the trim down again. Now what ?

Remember, nowhere does it mention the existence of the MCAS system, what its function is, and how it integrates into the system.
Wrong in every respect.

1) They did *not* before 'neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT' - the trim was still around 5 degrees out when the hit the CUT-OUTs.

2) The nose was not lowered in any way - they were still in a climb attitude - but they were pulling hard to maintain it (refer point #1).

3) You have to stop using manual trim for 5 seconds before MCAS switches on.

4) Although not mentioned by name, the AD gives enough of a functional description to know what it happening:
Note: The 737-8/-9 uses a Flight Control Computer command of pitch trim to improve longitudinal handling characteristics. In the event of erroneous Angle of Attack (AOA) input, the pitch trim system can trim the stabilizer nose down in increments lasting up to 10 seconds.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by richard C » Fri Oct 18, 2019 10:17 am

:oops: :oops:

Was working from memory and did not go through the whole thread to try and dig out the sequence.

They weren't climbing when they hit the ground, so I can't be completely wrong.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by heisan » Fri Oct 18, 2019 10:26 am

richard C wrote:
Fri Oct 18, 2019 10:17 am
They weren't climbing when they hit the ground, so I can't be completely wrong.
That was because:
1) they turned the cut-out switches off again (which is prohibited by the AD), and
2) when they turned the cut-outs off, rather than using manual electric trim to neutralise the trim forces, they spent what time they had trying to turn on the A/P (which the AD expressly says will not be available).

Once they did that, control forces became too great, and the aircraft pitched down (and too much to recover).
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Ugly Duckling » Fri Oct 18, 2019 11:17 am

Test pilots are the ones who are best qualified to mess around with the unpredictable flight characteristics of aircraft.
By the time it is in airline service the bugs and gremlins should have been clearly identified and the responses of the crew should be in muscle memory or at least a familiar item in the QRH. These 4 crewmembers were at best passengers with a view when the horns and lights started up.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Thermalator » Fri Oct 18, 2019 2:33 pm

richard C wrote:
Fri Oct 18, 2019 9:25 am
CarlGrobler58 wrote:
Fri Oct 18, 2019 8:48 am
So this system will override the pilot's uptrim being held on the yoke. So while you are trimming up the system trims down?
That is the sole purpose of the system -
- to continuously feed in nose-down pitch to prevent a stall, irrespective of the pilots actions, this state being determined by a single AOA sensor that had in both cases, failed.
Negative negative what heisan says deserves reiteration - all it needed was fly the plane & flick the trims while looking out the window setting throttles / pitch / airspeed to normal range - & don't fiddle/debug with anything until 15kft

Question what situations to they train crew not to DO NOTHING other than climb to safe altitude

**note I do realise the AD says trim cutout proc....BUT think about it, that is Boeing CYA because they are trying to bring it back to trim runaway procedure because that is their legal crutch in this mess. It is obvious that using trim runaway is suboptimal - I wonder if any operator thought about that.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Antman » Fri Oct 18, 2019 3:51 pm

rather than using manual electric trim to neutralise the trim forces
What manual electric trim???????
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by heisan » Fri Oct 18, 2019 4:08 pm

Antman wrote:
Fri Oct 18, 2019 3:51 pm
rather than using manual electric trim to neutralise the trim forces
What manual electric trim???????
The trim buttons on the yoke.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Antman » Fri Oct 18, 2019 4:18 pm

heisan wrote:
Fri Oct 18, 2019 4:08 pm
Antman wrote:
Fri Oct 18, 2019 3:51 pm
rather than using manual electric trim to neutralise the trim forces
What manual electric trim???????
The trim buttons on the yoke.
Ok here’s how it works, there are 2 trim rocker switches under your thumb.
Both are electric trim
1 Autopilot electric trim
2 Electric trim which the pilot uses to trim the stab electrically.

If the Stab Trim Cutout switches are turned off these two switches do not work, the only way you
Can trim the stab with the Cutout switches off is by manually rotating the big trim wheel on the pedestal.

Therefore
2) when they turned the cut-outs off, rather than using manual electric trim to neutralise the trim forces
Is not possible!
they spent what time they had trying to turn on the A/P (which the AD expressly says will not be available).
With the Cutout switches off no AP is available, any rated B737 pilot does not need an AD to tell them this.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by heisan » Fri Oct 18, 2019 4:25 pm

By 'cut-out switches off', i meant 'not cut-out' - sorry if I was unclear.

As I was trying to explain it:
'turn on cut-out switch' = activate cut-outs (deactivate electric trim)
'turn off cut-out switch' = deactivate cut-outs (activate electric trim)
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by Antman » Fri Oct 18, 2019 4:40 pm

heisan wrote:
Fri Oct 18, 2019 4:25 pm
By 'cut-out switches off', i meant 'not cut-out' - sorry if I was unclear.

As I was trying to explain it:
'turn on cut-out switch' = activate cut-outs (deactivate electric trim)
'turn off cut-out switch' = deactivate cut-outs (activate electric trim)
Then what you said is correct 8)

As I mentioned earlier, if you look at the ET crash out of Beirut
https://www.bea.aero/docspa/2010/et-b10 ... 125.en.pdf
You’ll also see the attempt to engage the autopilot as a remedy to there problem.

This points to a strong reliance on the autopilot at Ethiopian, which is probably reinforced in there S.O.P.S
and training. This is a very worrying modern trend at airlines.

Even Garmin are promoting this with the blue button on there latest autopilots which as I understand bring the aircraft
Back to strait and level at the push of a button.

Like other Elephants in the room the industry is aware of this problem.
https://www.flightglobal.com/news/artic ... ti-461057/

Yet the MPL is heavily promoted as means to crew the ever increasing number of aircraft.
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Re: Ethiopian Airlines plane crashes on way to Nairobi

Unread post by jimdavis » Fri Oct 18, 2019 6:21 pm

richard C wrote:
Fri Oct 18, 2019 10:03 am
Thanks for the new moniker, Jim - I like it !
Ha ha ha - sorry Richard. I was having a blonde moment! :lol:

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