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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 18th Mar 2019, 14:30
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Boeing tumbled early Monday on heightened scrutiny by regulators and prosecutors over whether the approval process for the company’s 737 Max jetliner was flawed.

A person familiar with the matter on Sunday said that the U.S. Transportation Department’s Inspector General was examining the plane’s design certification before the second of two deadly crashes of the almost brand-new aircraft.

Separately, the Wall Street Journal reported that a grand jury in Washington, D.C., on March 11 issued a subpoena to at least one person involved in the development process of the Max. And a Seattle Times investigation found that U.S. regulators delegated much of the plane’s safety assessment to Boeing and that the company in turn delivered an analysis with crucial flaws.

737 Max Is Turning Into a Major Problem for Boeing | Time
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Old 18th Mar 2019, 14:35
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Originally Posted by Sailvi767
Climbing controls speed? Only if you leave the thrust at a high power setting! Yes they should have adjusted power to maintain a reasonable speed. Itís called piloting!
You're mistaken, "climbing" (or, put more precisely) elevator/AOA control always controls speed. Of course, under the likely MCAS scenario discussed, they did not have AOA control and the airspeed was running away from them.

And thrust always controls vertical flight path, so if they reduced thrust they would have only hit the ground sooner. In a desperate fight for altitude, "piloting" would dictate maximum thrust.
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Old 18th Mar 2019, 14:48
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Originally Posted by Vessbot
You're mistaken, "climbing" (or, put more precisely) elevator/AOA control always controls speed. Of course, under the likely MCAS scenario discussed, they did not have AOA control and the airspeed was running away from them.

And thrust always controls vertical flight path, so if they reduced thrust they would have only hit the ground sooner. In a desperate fight for altitude, "piloting" would dictate maximum thrust.
But more speed when your stab trim is too nose down is your enemy. Reduction in speed would reduce the force to counter the nose down trim so 'piloting' would dictate reducing speed.
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Old 18th Mar 2019, 14:49
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Originally Posted by Vessbot
You're mistaken, "climbing" (or, put more precisely) elevator/AOA control always controls speed. Of course, under the likely MCAS scenario discussed, they did not have AOA control and the airspeed was running away from them.

And thrust always controls vertical flight path, so if they reduced thrust they would have only hit the ground sooner. In a desperate fight for altitude, "piloting" would dictate maximum thrust.
Having taught out of control flight in high performance aircraft I can tell you we never taught that. It’s also not taught in current airline simulator training. It is not what Boeing puts out. The last thing you want with trim stuck or running nose down is excessive speed. You control that with thrust. Again it’s called piloting. Had they reduce thrust and kept the speed back below 250 they would not have hit the ground at all. Control forces would have been much lighter. You have to establish the aircraft in a regime where it is controllable. Max thrust is the worst thing you could do in a nose down trim situation.
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Old 18th Mar 2019, 14:50
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Originally Posted by sky9
The 757 and 767 both have 3 channels.

If there are only 2 channels on a 737 A/P how does it do a CAT3 A and B autoland or is this another delegation of certification by the FAA?
Fail operation versus fail passive.
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Old 18th Mar 2019, 14:59
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Originally Posted by Ian W
But more speed when your stab trim is too nose down is your enemy. Reduction in speed would reduce the force to counter the nose down trim so 'piloting' would dictate reducing speed.
Yes but reducing thrust on the 737 creates a large nose down moment (pitch/power couple) so as Vessbott stated they would have just hit the ground sooner.

My experience of this is unusual attitude recovery during manual reversing air tests. Reducing thrust, if you're already using everything you have to keep the nose up, WILL result in a further nose down moment and no reduction in speed. They'd have been better off sticking the speed brakes up.

And in fact Boeing DO publish this in the QRH.
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Old 18th Mar 2019, 15:01
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Originally Posted by Sailvi767


Having taught out of control flight in high performance aircraft I can tell you we never taught that. Itís also not taught in current airline simulator training. It is not what Boeing puts out. The last thing you want with trim stuck or running nose down is excessive speed. You control that with thrust. Again itís called piloting. Had they reduce thrust and kept the speed back below 250 they would not have hit the ground at all. Control forces would have been much lighter. You have to establish the aircraft in a regime where it is controllable. Max thrust is the worst thing you could do in a nose down trim situation.
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In your proposed solution, had they reduced thrust what would have prevented them from diving into the ground at the high speed commanded by their low AOA?
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Old 18th Mar 2019, 15:07
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Originally Posted by Chesty Morgan
Fail operation versus fail passive.
I think here is a missunderstanding.
It's about channels not number of AP.

To my limited knowledge the 737 has no AP YAW CHANNEL, only roll and pitch.

Stand to be corrected.
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Old 18th Mar 2019, 15:08
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Originally Posted by gearlever
I think here is a missunderstanding.
It's about channels not number of AP.

To my limited knowledge the 737 has no AP YAW CHANNEL, only roll and pitch.

Stand to be corrected.
Yes you're quite right. My bad.
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Old 18th Mar 2019, 15:11
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Fail-operational autopilot is a customer option on the NG and MAX since 2003. Not many airlines have taken the option though...
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Old 18th Mar 2019, 15:15
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Originally Posted by Chesty Morgan
Yes but reducing thrust on the 737 creates a large nose down moment (pitch/power couple) so as Vessbott stated they would have just hit the ground sooner.
You're right about the thrust pitch couple, but I'm not even talking about that yet, I'm only taking talking about the basic effect of excess thrust on flight path angle.

And to that end, I'm afraid spoilers won't help either, but they'll certainly be a lot less harmful than a thrust reduction with underslung engines.

Unless the pitching moment they add is nose up, which is an answer I don't know. But a nose up pitching moment is what we want, both for the instantaneous normal acceleration upward, and the energy-state perspective on reducing airspeed.
[/QUOTE]
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Old 18th Mar 2019, 15:22
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Originally Posted by Judd
It seems both aircraft were porpoising before going in. Is it possible the crews were trying to overcome excessive aerodynamic loads on the stabiliser which had gone towards the forward limit, after cutting electrical power to the stab trim motor and were now trying to wind manual trim during the unloading maneuver called roller coasting? See extract from a Boeing 737-200 PTM date 1982 and migrated from Tech Log
Extract from the Boeing 737-200 Pilot Training Manual February 1982 page 04.80.31. Edited for brevity
Runaway and Manual Stabiliser - Recovery from Severe Out-of-Trim
"In an extreme nose-up out-of-trim condition, requiring almost full forward control column, decelerate, extend the flaps and/or reduce thrust to a minimum practical setting consistent with flight conditions until elevator control is established. Do not decrease airspeed below the minimum maneuvering speed for the flap configuration. A bank of 30 degrees or more will relieve some force on the control column. This, combined with flap extension and reduced speed should permit easier manual trimming.

If other methods fail to relieve the elevator load and control column force, use the "roller coaster" technique. If nose-up trim is required, raise the nose well above the horizon with elevator control. Then slowly relax the control column pressure and manually trim nose-up. Allow the nose to drop below the horizon while trimming. Repeat this sequence until the airplane is trim.
Will it worked in such time critical at 1000 ft with 360 knot airspeed with extreme full down trim?
maybe neutralized with up with column electrical trim first than kill the 2 switches like jt043. Itís already proven
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Old 18th Mar 2019, 15:27
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Originally Posted by Aloha_KSA
This should be boxed as a memory item, like runaway stab trim.
It is runaway stab trim...
Maybe not all at once, but if it is not doing what you want, then it is out of control.
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Old 18th Mar 2019, 15:31
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Originally Posted by Vessbot
And to that end, I'm afraid spoilers won't help either, but they'll certainly be a lot less harmful than a thrust reduction with underslung engines.

Unless the pitching moment they add is nose up, which is an answer I don't know.
[/QUOTE]
They do cause a pitch up.
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Old 18th Mar 2019, 15:46
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Originally Posted by flyingchanges
It is runaway stab trim...
Maybe not all at once, but if it is not doing what you want, then it is out of control.
That is not what Boeing states in its condition for the memory items:

"Condition: Uncommanded stabilizer trim movement occurs continuously."
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Old 18th Mar 2019, 15:48
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VESBOT states:
You're mistaken, "climbing" (or, put more precisely) elevator/AOA control always controls speed. Of course, under the likely MCAS scenario discussed, they did not have AOA control and the airspeed was running away from them.

And thrust always controls vertical flight path, so if they reduced thrust they would have only hit the ground sooner. In a desperate fight for altitude, "piloting" would dictate maximum thrust.


If the above is true, when you are ready for take off, try this:

Pump the elevators up and down until you has reached VR, then when you reach VR, shove the throttles to maximum to rotate.
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Old 18th Mar 2019, 15:49
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Originally Posted by Vessbot
In your proposed solution, had they reduced thrust what would have prevented them from diving into the ground at the high speed commanded by their low AOA?
They were at high speed, reducing thrust would have had almost no effect on pitch. Itís done every single day on every airline flight. The stabilizer at high speeds is extremely powerful in control of pitch. Engine thrust is negligible. Pulling the power from takeoff power to cruise power for 250 would not even be noticed. In normal ops maybe 1 click of trim moving the stab .01.
I think you are getting confused with recovering from flight near stall with a nose up attitude and high AOA. In that specific situation slamming the power to max will cause the nose to pitch up further because the stabilator has far less control authority.
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Old 18th Mar 2019, 15:51
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Originally Posted by warbirdfinder
VESBOT states:
You're mistaken, "climbing" (or, put more precisely) elevator/AOA control always controls speed. Of course, under the likely MCAS scenario discussed, they did not have AOA control and the airspeed was running away from them.

And thrust always controls vertical flight path, so if they reduced thrust they would have only hit the ground sooner. In a desperate fight for altitude, "piloting" would dictate maximum thrust.


If the above is true, when you are ready for take off, try this:

Pump the elevators up and down until you has reached VR, then when you reach VR, shove the throttles to maximum to rotate.
You ever try taking off at idle thrust?
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Old 18th Mar 2019, 16:01
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Does anyone know ETs procedure for Airspeed Disagree? Experiencing that error due to AoA vane failure, would they have simply gone for ex 80% N1, and then Flaps Up to keep bits from coming off?

At which point theyíre soon rocketing along, MCAS kicks in, and they canít climb?
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Old 18th Mar 2019, 16:03
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Originally Posted by Chesty Morgan
Yes but reducing thrust on the 737 creates a large nose down moment (pitch/power couple) so as Vessbott stated they would have just hit the ground sooner.

My experience of this is unusual attitude recovery during manual reversing air tests. Reducing thrust, if you're already using everything you have to keep the nose up, WILL result in a further nose down moment and no reduction in speed. They'd have been better off sticking the speed brakes up.

And in fact Boeing DO publish this in the QRH.
In fact the forward and higher placement of the engines that required MCAS because of their aerodynamic lift at high AoA, has also significantly reduced the pitch/power couple as the engines are closer to the vertical midline. In any case the idea is not to get to the full thrust position in the first place. As stated up thread the aircraft might have been controllable in pitch at a reduced speed.
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