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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 14th Mar 2019, 00:07
  #1221 (permalink)  
 
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Originally Posted by Recidivist View Post
AoA says nose is high
AoA doesn't tell you anything about pitch attitude, nor vice versa. Ask Air France.

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Old 14th Mar 2019, 00:08
  #1222 (permalink)  
 
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Looks like the last U.S. MAX to land with pax today is WN2569 OAK-EWR.

The other MAX's still up are two Air Canada's, three WestJet's and three Sunwings.


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Old 14th Mar 2019, 00:09
  #1223 (permalink)  
 
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Please sit back and relax - nothing could possibly go wrong go wrong go wrong ( that was in vogue in the 1960's on the Boeing SST program ...

meanwhile back at the ranch

Boeing 737 MAX - Differences

Maneuvering Characteristics Augmentation System (MCAS)

MCAS (Maneuvering Characteristics Augmentation System) is implemented on the 737 MAX to enhance pitch characteristics with flaps UP and at elevated angles of attack. The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors and during flaps up flight at airspeeds approaching stall. MCAS is activated without pilot input and only operates in manual, flaps up flight. The system is designed to allow the flight crew to use column trim switch or stabilizer aislestand cutout switches to override MCAS input. The function is commanded by the Flight Control computer using input data from sensors and other airplane systems.The MCAS function becomes active when the airplane Angle of Attack exceeds a threshold based on airspeed and altitude. Stabilizer incremental commands are limited to 2.5 degrees and are provided at a rate of 0.27 degrees per second. The magnitude of the stabilizer input is lower at high Mach number and greater at low Mach numbers. The function is reset once angle of attack falls below the Angle of Attack threshold or if manual stabilizer commands are provided by the flight crew. If the original elevated AOA condition persists, the MCAS function commands another incremental stabilizer nose down command according to current aircraft Mach number at actuation.
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Old 14th Mar 2019, 00:10
  #1224 (permalink)  
 
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SLF here, please be gentle!
Too many pages, not enough time, but it seems to me that the MCAS is functioning solely on inputs about the attitude (AoA) of the airframe in one direction only. No attention appears to be paid to the position of the airframe in space - i.e. is altitude decreasing? AoA says nose is high but longitudinal gyro disagrees and says flight is level? Inertial Nav Systems have been around for a long time - back when I worked in the aviation industry. OK, that might be too expensive, but my yacht had a gyrocompass that cost about $100 as part of the autohelm. Why are these simple technologies not used for cross-checking of something mission critical like AoA? Before pushing the nose down, it would be helpful to know where it was pointing beforehand. And how could an automated system be allowed to drive the nose down while the altimeter shows altitude decreasing and acceleration increasing - the end result is inevitable!
It is not as easy, remember there are a bunch of certification rules that basically require the algorithms to be simple enough and predictable enough.
The altitude does not change anything to the problem, you could be stalling when recovering from a descent if you pull the stick too much, in that case the airplane is still in descent. So you have to rely on the AOA. You cannot rely on the gyro because the angle of attack and the attitude are not the same thing, for example if you get a sudden strong updraft your angle of attack increases but your gyro does not show that change.

It is a complex problem. There are no easy solutions.
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Old 14th Mar 2019, 00:15
  #1225 (permalink)  
 
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I wonder why MCAS is the only system in the aircraft that bypasses the Control Column Cutout Switches (and therefore the STAB OVRD switch). Normally a pilot pulling back on the control column couldn't trim nose down even if he tried. And vice-versa for push-down. However MCAS can freely trim down even if pilot is pulling back.



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Old 14th Mar 2019, 00:19
  #1226 (permalink)  
 
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Originally Posted by DaveReidUK View Post
AoA doesn't tell you anything about pitch attitude, nor vice versa. Ask Air France.
Ah, sorry, poor wording. I was imputing nose high from high AoA - not necessarily so, but layman language.
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Old 14th Mar 2019, 00:21
  #1227 (permalink)  
 
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Originally Posted by positiverate20 View Post
I know there's little evidence at this stage for this tragedy, but to elaborate and hypothesise about MCAS function:

1. MCAS activated by errant AoA vane data. (This same data may also lead to warnings such as stall etc.)

2. So, by the time you run through checklist, source the problem and stop the MCAS from further inputs by flicking the Stab trim cutout, the stab is already at X nose down.

3. At relatively low speed you're able to manage this by pulling back on the yoke, and the now fixed stab angle may even go unnoticed and forgotten about for a while

4. Additional engine power may already have been applied, but, if not, you do so now as you need some height, especially with advancing terrain and the loss of altitude that you'd suffered.

5. The effects of the engine cowling on aerodynamics, as stated in the comment above, helps lift, as does the thrust moment created by the engines

6. You think you have the problem somewhat under control compared to the situation you were in a minute ago. You've now been able to climb and seem to have relatively stable manual control.

7. Now you're at Y feet, (still with X nose down stab trim) with an increased airspeed of Z, up until now has been controllable due to your elevator inputs being assisted by thrust moment and engine aerodynamics, but, at this new increased airspeed and increased altitude the yoke is becoming even more difficult to keep holding back. The stab is still in the same X nose down it was when you switched the cut-outs, and up until now you mightn't have thought about it because you'd disabled it- in accordance with the checklist.

8. You think about returning and getting this back on the ground

9. Once you level off, or even before then, with that stab STILL at X nose down (now with a much higher airspeed component) there's only one place you're going. Once this vertical direction change has momentum there's now no chance, no elevators in the world are going to help you.

Look at the memory item for stab runaway- i.e.- not told to manually wind back trim wheel, the instruction is to "grab and hold".

All this could be caused by one errant sensor? Madness that it was certified.
What happened to one of your first priorities on an airplane that requires the pilot to manage pitch trim? If steady column forces are present, pitch trim should be used to drive the stabilizer so that those column forces are relieved. I concur with the criticism that with MCAS as currently implemented we can get headed down this path as a result of one errant sensor, but I don't see that the eventual result should put the airplane so far out of trim that pitch control power via the column is exhausted. MCAS moves the stabilizer, but does not interfere with the pilots ability to override and move the stabilizer back to the proper trim position.
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Old 14th Mar 2019, 00:26
  #1228 (permalink)  
 
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Compared to the 1979 Chicago DC-10 crash when it took 12 days for the FAA to ground the DC-10, 3 days is much faster.

If I were a Boeing manager, I'd much rather deal with a temporary grounding than a third crash.

Corporate memory fades over time, engineers with scar tissue retire and MBAs pinch harder on pennies.

The 787 battery wake up call seems to have been treated as a one off without a deeper look into how that design snuck past the DERs.
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Old 14th Mar 2019, 00:26
  #1229 (permalink)  
 
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Originally Posted by jagema View Post
I wonder why MCAS is the only system in the aircraft that bypasses the Control Column Cutout Switches (and therefore the STAB OVRD switch). Normally a pilot pulling back on the control column couldn't trim nose down even if he tried. And vice-versa for push-down. However MCAS can freely trim down even if pilot is pulling back.
The requirement compliance that MCAS was introduced to address can involve the column being further aft than the position of the column cutout switch. Were MCAS subject to being interrupted by that switch, it would not be able to do the job for which it was designed.
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Old 14th Mar 2019, 00:29
  #1230 (permalink)  
 
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I think that reaction time plays a big factor in this case.

You jump in an airplane thet flew in, and rght after rotation ( if all posted data are correct) you get an airframe that does not want to climb.
Meters above ground you soldier on fighting and throubleshooting untill you loose it after a mere 6 minutes of pure surprice/panic.

In this case( again if all info posted is correct) you have no room, no time, no "spare" altitude.
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Old 14th Mar 2019, 00:30
  #1231 (permalink)  
 
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Originally Posted by jagema View Post
I wonder why MCAS is the only system in the aircraft that bypasses the Control Column Cutout Switches (and therefore the STAB OVRD switch). Normally a pilot pulling back on the control column couldn't trim nose down even if he tried. And vice-versa for push-down. However MCAS can freely trim down even if pilot is pulling back.
Not quite correct, the Speed Trim System (STS) will trim in opposition to control column movement. B737 pilots get used to seeing the trim wheel move without a trim input and accept this as normal. I believe this is a very subtle form of conditioning and normalization that is likely to be relevant to at least the Lionair JT610 accident.
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Old 14th Mar 2019, 00:31
  #1232 (permalink)  
 
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Corporate memory fades over time, engineers with scar tissue retire and MBAs pinch harder on pennies.

The 787 battery wake up call seems to have been treated as a one off without a deeper look into how that design snuck past the DERs.
His name was Ali Bahrami, at the FAA. Retired shortly after and hired by a lobbyist group funded by Boeing. Surprise!

Last edited by Rated De; 14th Mar 2019 at 00:50.
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Old 14th Mar 2019, 00:32
  #1233 (permalink)  
 
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Originally Posted by RatherBeFlying View Post
Compared to the 1979 Chicago DC-10 crash when it took 12 days for the FAA to ground the DC-10, 3 days is much faster.

If I were a Boeing manager, I'd much rather deal with a temporary grounding than a third crash.

Corporate memory fades over time, engineers with scar tissue retire and MBAs pinch harder on pennies.

The 787 battery wake up call seems to have been treated as a one off without a deeper look into how that design snuck past the DERs.
Big difference between 787 battery issue and 737MAX Lion Air event. With the battery a subsystem component had a failure that was thought to have such a low probability as to not require consideration. With the 737MAX system the expected/assumed pilot response to a failure that was considered during design did not hold true. No pilot involvement with the battery failure consequences. Flight crew very much involved in the MCAS with errant AOA sensor consequences.
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Old 14th Mar 2019, 00:35
  #1234 (permalink)  
 
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Originally Posted by CurtainTwitcher View Post
Not quite correct, the Speed Trim System (STS) will trim in opposition to control column movement. B737 pilots get used to seeing the trim wheel move without a trim input and accept this as normal. I believe this is a very subtle form of conditioning that is likely to be relevant to at least the Lionair JT610 accident.
STS is subject to column cutout such that large column motion in opposition to STS stabilizer command will stop STS command. Not true with MCAS. This is an important differnce between these two automatic stabilizer control functions.
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Old 14th Mar 2019, 00:39
  #1235 (permalink)  
 
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The 787 battery wake up call seems to have been treated as a one off without a deeper look into how that design snuck past the DERs.
IF i recall- at that time the DER " system" had been changed within Boeing as to who really had the last word and the DER as such had a new 3 or 4 letter designation.

With more a** covers needed.

And the 787 was neasrly immediately grounded despite no injuries.
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Old 14th Mar 2019, 00:44
  #1236 (permalink)  
 
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Originally Posted by Rated De View Post
His name was ALi Bahrami, at the FAA. Retired shortly after and hired by a lobbyist group funded by Boeing. Surprise!
He's back at the FAA, in charge of safety.
https://www.ainonline.com/aviation-n...viation-safety
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Old 14th Mar 2019, 00:49
  #1237 (permalink)  
 
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Originally Posted by brak View Post
He's back at the FAA, in charge of safety.
https://www.ainonline.com/aviation-n...viation-safety
Revolving doors and all.....
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Old 14th Mar 2019, 00:50
  #1238 (permalink)  
 
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Originally Posted by FCeng84 View Post
STS is subject to column cutout such that large column motion in opposition to STS stabilizer command will stop STS command. Not true with MCAS. This is an important differnce between these two automatic stabilizer control functions.
Thank you for the clarification. Again, this highlights insidious nature of system's subtlety.
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Old 14th Mar 2019, 00:54
  #1239 (permalink)  
 
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I think Boeing's ballsed this up - and the FAA have a lot of reflecting to do on the overwhelming power of public sentiment versus the facts.
There comes a point in crisis management where you must address the perceptions, arguing the facts is useless.
Few if any will likely share this sentiment, but I feel for Boeing's PR team at the moment.
As a former corporate spin doctor these crises are horrific to manage.
The public baying for your blood.
Investors trashing your stock.
Politicians jumping on the bandwagon.
And nearly always - panicked and agitated senior managers, and others right up to Board level, jumping in, trying to do your job for you, ignoring advice and only making a bad situation worse.
Seen it and lived it so, so many times - and it's always the same.
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Old 14th Mar 2019, 00:54
  #1240 (permalink)  
 
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Originally Posted by atakacs View Post
As for the Ethiopian crash we are way too early to draw any conclusion. An immediate airspace ban of the whole fleet is utter madness.
Nobody has drawn any conclusion from the ET-302 crash.

However the Lion Air crash and investigation has revealed not only a failed part but also a possibility of a serious design problem with the 737 MAX. Now that another 737 MAX of a similar age has crashed in not only the same phase of flight but from what information we do have, in a similar way (unreliable airspeed and difficulty gaining height) we have to take seriously the possibility that the same thing caused both crashes. Added to that, the short life of the model gives it a very high 'fatal crashes per million flights' statistic.

Given all of the above along with the fact that this isn't simply a batch of dodgy AoA sensors, but a possible design fault that could affect every aircraft in the fleet, it would be an act of sheer folly not to ground the entire fleet.

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