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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 16th Mar 2019, 16:21
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Originally Posted by ernst_mulder
A (possibly stupid) question from SLF,

What I am wondering about is why, after a struggle with MCAS, the plane ends up in a nosedown dive. Wouldn't the pilots in principle be able to keep fighting the unwanted trim commands indefinitely? Also earlier in this thread I read that it is possible to fly an airplane even with a full downward trimmed HS. Could another mechanical problem be the cause, i.e. elevator(s) breaking off after too much stress trying to compensate for the full downward trimmed HS?
The faster that the plane is going the greater the force required to oppose it and the more violent the reaction of the plane to the control surface, At low altitude and high speed it would be just about impossible to either overcome the stick force or to recover even if you could do so. The two obvious questions are why didn't the plane gain altitude along the way and why was it going so fast at low altitude if in fact it couldn't climb.
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Old 16th Mar 2019, 16:22
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This from Avweek Flash Report
Investigators probing the wreck of Ethiopian Airlines Fight 302 have reportedly recovered the airplane’s trim jackscrew and found it set to a nose-down position. This is similar to the jackscrew position found in the Lion Air crash last October and may be the additional evidence that convinced the FAA to ground the Boeing 737 MAX 8 and 9 series aircraft.

The Ethiopian MAX 8 crashed Sunday shortly after takeoff from Addis Ababa, killing all 159 people aboard. On Oct. 29, 2018, Lion Air JT 610, a nearly new MAX 8, crashed into the Java Sea under what appear to be strikingly similar circumstances. All 189 people aboard that aircraft were also killed.

NBC News reported Friday that the jackscrew was recovered by investigators in sufficiently intact condition to determine the aircraft was trimmed nose-down when it impacted in an open field southeast of Addis Ababa. This may confirm that the flight crew was struggling with a runaway condition.

Whatever brought down the flight apparently developed right after takeoff. On climbout, one of the pilots, possibly the captain, radioed the tower “Break break, request back to home.” He requested an immediate vector back to the departure airport. Controllers noticed that the flight was flying wide altitude excursions and ADS-B data released a day after the crash revealed similar vertical speed excursions and excessive airspeed for such a low altitude.

The flight data and cockpit voice recorders have been sent to Paris where the French BEA is reviewing the data.j
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Old 16th Mar 2019, 16:53
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Originally Posted by ernst_mulder
A (possibly stupid) question from SLF,

What I am wondering about is why, after a struggle with MCAS, the plane ends up in a nosedown dive. Wouldn't the pilots in principle be able to keep fighting the unwanted trim commands indefinitely? Also earlier in this thread I read that it is possible to fly an airplane even with a full downward trimmed HS. Could another mechanical problem be the cause, i.e. elevator(s) breaking off after too much stress trying to compensate for the full downward trimmed HS?
Yes, the pilot could keep counteracting the MCAS input with equal and opposite trim, and get into a trim cycle where, while the ride is wild, control is never lost until the electric trim is shut off or by flap selection for landing. Remember the MCAS function uses the high trim rate and can put in up to 2.5 degrees each cycle, so the pilot's trim inputs counteracting each cycle need to be fairly large. That is what the crew apparently successfully did in the flight prior to the Lion Air accident flight. Remember, by putting in opposite trim, the pilot interrupts the MCAS function and causes it to re-arm for another cycle, which will be triggered five seconds after trim switch release if the MCAS logic is still satisfied (manual flight, flaps up, same side AOA sensed beyond some threshold). However, if on repeated successive cycles of MCAS input, the pilot fails to fully reverse the amount of trim MCAS has put in, the nose down trim will continue to build until the column input can no longer override its effect. This can happen in just a few MCAS cycles.

Think of this in terms of the total scenario that results from an erroneous high AOA input to the flight control computer that is in control as opposed to imagining flying along just fine and MCAS starts acting up. The stick shaker activates on rotation, and the airspeed difference between the left and right side increases as speed builds due to the AOA correction in the air data computation logic. The pilot recognizes he has unreliable airspeed, and is getting stick shaker and possibly other aural warnings about speed (not sure about that last part), so he flies manually and never engages the autopilot He thinks he's on the verge of stalling, and despite keeping the nose down and accelerating, the stick shaker remains on and he has unreliable airspeed. After a minute or two he gets to the speed where he's getting cues to pull the flaps up, so he does, and now MCAS starts putting in trim inputs on top of his already high workload and stress. Apparently an assumption was made that the population of crews flying the 737 Max could consistently handle this situation correctly given the additional information put out by Boeing after the Lion Air accident.
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Old 16th Mar 2019, 17:30
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IMHO that makes a lot of sense, on several levels. Certainly the ‘persistence’ of MCAS demanding nose down would require a LOT of persistent winding of manual trim if MCAS was not disabled. That incessant input (5 seconds?) is hardly helpful if it takes more than 5 secs to wind it off ... while struggling with everything else ... and then have to do it all again!
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Old 16th Mar 2019, 17:41
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Originally Posted by MPN11
IMHO that makes a lot of sense, on several levels. Certainly the Ďpersistenceí of MCAS demanding nose down would require a LOT of persistent winding of manual trim if MCAS was not disabled. That incessant input (5 seconds?) is hardly helpful if it takes more than 5 secs to wind it off ... while struggling with everything else ... and then have to do it all again!
Well until you flip the stab trim cutout switches and all become right with the world. So simple, so quick IF you know what you are doing!

Boeing felt this procedure was enough, especially after all MAX pilots worldwide were given specific information on how to deal with inadvertent MCAS activation to allow the plane to continue to fly until their comprehensive fix was implemented by April of 2019 but having it happen again (assuming this was an MCAS issue) clearly demonstrates that some pilots qualified in the MAX canít handle the task loading and intrepret the situation well enough to apply the simple fix so hence the plane remains grounded until the plane itself can be smarter so as to not require pilots to interpret their own jet. Iím conflicted about many things in this accident: the engineers who couldnít see the danger in allowing a system to apply overwhelming trim in response to a single sensor input, Boeing management deciding before Lion Air we didnít need to know about MCAS, and yes the pilots who absolutely should be able to diagnose a trim issue and how to stop it in 7-12 minutes of time before crashing their jet even if they didnít know WHY the trim was misbehaving. Lots of blame to go around but letís get a good airplane fixed and flying again.
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Old 16th Mar 2019, 17:54
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Originally Posted by Dave Therhino
Yes, the pilot could keep counteracting the MCAS input with equal and opposite trim, and get into a trim cycle where, while the ride is wild, control is never lost until the electric trim is shut off or by flap selection for landing. Remember the MCAS function uses the high trim rate and can put in up to 2.5 degrees each cycle, so the pilot's trim inputs counteracting each cycle need to be fairly large. That is what the crew apparently successfully did in the flight prior to the Lion Air accident flight. Remember, by putting in opposite trim, the pilot interrupts the MCAS function and causes it to re-arm for another cycle, which will be triggered five seconds after trim switch release if the MCAS logic is still satisfied (manual flight, flaps up, same side AOA sensed beyond some threshold). However, if on repeated successive cycles of MCAS input, the pilot fails to fully reverse the amount of trim MCAS has put in, the nose down trim will continue to build until the column input can no longer override its effect. This can happen in just a few MCAS cycles.
Absurd design philosophy as I said before. A workaround of the worst sort... and naive in concept. Worse than a bodge* which can be seen for what it is !

* from Chiltern Beechwood Chairmakers (bodgers)
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Old 16th Mar 2019, 18:16
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Originally Posted by ernst_mulder
A (possibly stupid) question from SLF,

What I am wondering about is why, after a struggle with MCAS, the plane ends up in a nosedown dive. Wouldn't the pilots in principle be able to keep fighting the unwanted trim commands indefinitely? Also earlier in this thread I read that it is possible to fly an airplane even with a full downward trimmed HS. Could another mechanical problem be the cause, i.e. elevator(s) breaking off after too much stress trying to compensate for the full downward trimmed HS?
The pilots of Lion Air kept trimming up, but the manual trim bursts were shorter, which was apparently enough for the trim to completely run away. Perhaps busy with something else? Without cvr transcription we (the public) don't know, but the investigators and Boeing probably do.

Originally Posted by MPN11
IMHO that makes a lot of sense, on several levels. Certainly the ‘persistence’ of MCAS demanding nose down would require a LOT of persistent winding of manual trim if MCAS was not disabled. That incessant input (5 seconds?) is hardly helpful if it takes more than 5 secs to wind it off ... while struggling with everything else ... and then have to do it all again!
Same as above, look at the lion air FDR data. It's a horrible situation to be in.

Originally Posted by Dave Therhino
Yes, the pilot could keep counteracting the MCAS input with equal and opposite trim, and get into a trim cycle where, while the ride is wild, control is never lost until the electric trim is shut off or by flap selection for landing.
The Lion Air crew briefly extended the flaps and got the situation under control, but then they retracted them agin :-(
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Old 16th Mar 2019, 19:10
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... which comment takes me back to a post I made ages ago ... a BIG button that says “I have control” and stops all the trim and autopilot automacity at a stroke. Then the guys at the front have a chance to fly the aircraft.

Or is that a “Bad thing”?
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Old 16th Mar 2019, 19:20
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I don't think it's necessarily a bad thing but in this case MCAS is a certification requirement. Is it allowed to be deactivated? I don't know.
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Old 16th Mar 2019, 19:26
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I read somewhere in the thread that MCAS was only needed to pass parts of the certification requirements, specifically stall prevention during turns at steep bank angles. Is this correct assumption? If true, would it be possible for Boeing to just add bank angle limits to the list of MCAS "engagement" prerequisites like flaps up and AP off? It would solve the cert. problem and maybe the presumed (because not clear yet) causes of both accidents.

If so, what would your view as prof. pilots be to such a "fix"
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Old 16th Mar 2019, 19:38
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Does the max have the EFS module that the NG has? Where by control forces double with hydraulics when approaching the stall! Been reading it in Fcom, and it is vague like most stuff in fcom..

if they had nose down trim from mcas, and efs was adding control forces, they would not stand a chance...
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Old 16th Mar 2019, 19:51
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Originally Posted by Chesty Morgan
I don't think it's necessarily a bad thing but in this case MCAS is a certification requirement. Is it allowed to be deactivated? I don't know.
As I’m understanding things, yes ... it can be deactivated by two guarded switches on the pedestal, provided the crew know about it and have time and hands free to use them whilst both also hauling on the yoke and fighting trim with the yoke switches or the trim wheel which get over-ruled every 5 seconds by Stab Trim through MCAS and wondering what’s going on. Or by dropping a notch of flap. Or autopilot on (or was that off?). Simple, isn’t it!

Am I right?

Anyway, back to the professionals who fly these things. But the various inputs here have been fascinatingly instructive.
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Old 16th Mar 2019, 19:59
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Originally Posted by UAV689
Does the max have the EFS module that the NG has? Where by control forces double with hydraulics when approaching the stall! Been reading it in Fcom, and it is vague like most stuff in fcom..

if they had nose down trim from mcas, and efs was adding control forces, they would not stand a chance...
Yes, the EFS is present in the Max.
And it is 4 times the normal forces, in both models.
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Old 16th Mar 2019, 20:12
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Originally posted by 'derjodel' #1588

Right, ET also managed to put 787 on fire while there were others flying about without an issue. Sheer incompetency!

Seriously, what is the data which leads to "questionable safety record" conclusion ET? And please adjust for hijackings, unless you are going to claim somehow those are also ET's fault.

In reality, if you take out the recent MAX crash and the 96 hijacking, they have about 200 fatalities since 1948. Questionable safety!?




What about the 2010 737 crash in Lebanon? Looking at that accident report it does not put ET in a good light.

Last edited by esoterex; 16th Mar 2019 at 20:45. Reason: edited for clarity
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Old 16th Mar 2019, 20:18
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Originally Posted by MPN11
Am I right?
Doh, yes of course! I claim distraction by the Calcutta Cup (FFS!).
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Old 16th Mar 2019, 20:50
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If it turns out to be mcas for this flight loss and the stab trim switches are found to be in the on position then the pilots are 100% to blame for all those lost lives.
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Old 16th Mar 2019, 20:59
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The ET B787 fire in LHR? thought that was due to a ELT battery shorting out.
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Old 16th Mar 2019, 21:00
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Originally Posted by reamer
If it turns out to be mcas for this flight loss and the stab trim switches are found to be in the on position then the pilots are 100% to blame for all those lost lives.
Tosh. The manufacturer has produced a sub-standard product, pushing enhanced responsibility on aircrews. There are many layers of responsibility here, the first being Boeingís insistence on polishing-off a 50+ year-old aircraft by adding bigger engines bringing questionable stability and mitigating it all with a poorly thought-through Ďsafety systemí (MCAS).
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Old 16th Mar 2019, 21:02
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Originally Posted by donal r james
The ET B787 fire in LHR? thought that was due to a ELT battery shorting out.
Indeed, poorly implemented risk assessments at design level. As for the firproof box and exhaust solution, one needs to ask the FAA whty they basically accepted that an airborne fire scenario was suddenly acceptable. (Thereís a REALLY long thread somewhere about that).
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Old 16th Mar 2019, 21:10
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AvHerald reporting the CVR has been read out and the data given to theEthiopian authorities without being listened to by the French. The work on the FDR is ongoing.
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