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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 16th Mar 2019, 18:20
  #1621 (permalink)  
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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, 18:26
  #1622 (permalink)  
 
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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, 18:38
  #1623 (permalink)  
 
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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, 18:51
  #1624 (permalink)  
 
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Originally Posted by Chesty Morgan View Post
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, 18:59
  #1625 (permalink)  
 
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Originally Posted by UAV689 View Post
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, 19:12
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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 19:45. Reason: edited for clarity
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Old 16th Mar 2019, 19:18
  #1627 (permalink)  
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Originally Posted by MPN11 View Post
Am I right?
Doh, yes of course! I claim distraction by the Calcutta Cup (FFS!).
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Old 16th Mar 2019, 19:50
  #1628 (permalink)  
 
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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, 19:59
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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, 20:00
  #1630 (permalink)  
 
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Originally Posted by reamer View Post
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 Boeing’s 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 ‘safety system’ (MCAS).
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Old 16th Mar 2019, 20:02
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Originally Posted by donal r james View Post
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. (There’s a REALLY long thread somewhere about that).
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Old 16th Mar 2019, 20:10
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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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Old 16th Mar 2019, 20:11
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Originally Posted by esoterex View Post
What about the 2010 737 crash in Lebanon? Looking at that accident report it does not put ET in a good light.
You can‘t draw conclussions on cherry-picked data. This way you introduce bias to the sample and of course data confirms your bias!

that said, ET409 final report is a fascinating read. I‘m just going over it and what standa out is:
- captains behavior seems to indicate he was somehow incapacitated (eg slow and wrong reactions to bank angle); what‘s more, he complained he could not sleep due to evening meal! It could be he was totally zombied due to insomnia
- twice on cvr recording he‘s asking about „what‘s that“ to which FO doesnt even react... insomnia induced hallucinations? Report offers no explaination
- he hand flew which was against SOP for IMC

now for the interesting part:
- TO trim selection was wrong for unexplained reasons(??)
- period of 3” a trim up which resulted in an increase of pitch trim from 7.9 to 8.8 units and an airspeed of 196 Kts. That manual trim command was the last one commanded by the crew during the flight and resulted in the aircraft computer memorizing that speed as the one the crew wanted to maintain, despite the different speed selected on the MCP19.- AP could not be engaged due to column forces against trim
- toga was selected
- At the same time, as the speed started to increase beyond 195 Kts, the speed trim commanded a nose up trim input increasing the pitch trim from 8.2 to 9.3 units at 00:40:37, resulting in a further increase in the aircraft pitch up tendency. The crew did not take any action to re-trim the aircraft to the desired speed, so, once the nose down pressure was released on the control column, the aircraft pitch started to increase again and became close to 30° up

in essence, possibly very similar to mcas, but in reverse: sts remebered a certain speed and stalled the airplane trying to maintain it. With toga selected sts had to compensate plenty of power with trim.

Wow.

I don‘t know if last manual trim also sets target speed for mcas? In case of ET with full thrust, wouldn’t that set higher target sped with every manual up trim? And as soon as you pull up and reduce speed you’d get hit with more trim to get to the target speed? That certainly would escalate very quickly once speed starts building up and could explain why the crews could not handle the plane. But this could also be nonsense, I don’t know how the systems behave.
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Old 16th Mar 2019, 20:11
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Originally Posted by reamer View Post
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.
What an ignorant comment. From a systems perspective, if aircraft design results in a situation that is 100% reliant on crew to flick the stab trim switches off, in a time critical, startling, highly dynamic scenario, the fault is almost entirely with the design of the aircraft. I thought we'd moved on a bit from the 'blame the human at the end of the error chain' mentality, but clearly some among us still have some way to go.
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Old 16th Mar 2019, 20:19
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Question from an SLF: Is it normal that you can trim an aircraft so far that you could not counteract the trim with the yoke, or is it a special feature of the 737?

What's the point of having a trim range exceeding the elevator authority? Are there any situations where this is needed?
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Old 16th Mar 2019, 20:21
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The ELT (Emergency Location Transmitter) is completely independent emergency equipment system. Nothing to do with the two main electrical system batteries that have ended up in a stainless steel fire proof box. The initial fix there was to remove the ELT or the battery.
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Old 16th Mar 2019, 20:34
  #1637 (permalink)  
 
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stainless steel fire proof box
Nothing is fire proof - it may be fire resisting but everything melts at some point. The point is, does a burning battery have the heat to melt stainless steel?

Last edited by A. Muse; 16th Mar 2019 at 20:36. Reason: quote in wrong place
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Old 16th Mar 2019, 20:39
  #1638 (permalink)  
 
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Thought Experiment

Your lined up on the runway. All normal. Advance power. Liftoff. Now your initial climbing out. “STALL STALL” HORN STICK SHAKER

Firewall the throttles
Pitch to respect stick shaker
Look around. What’s going on?

So my question is what do you do?

???
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Old 16th Mar 2019, 20:39
  #1639 (permalink)  
 
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I had wondered about a pitot issue given the IAS problems reported, and wondered at the chances of additional hardware failure w AoA vane tripping MCAS....

...but does this show that IAS Disagree can in fact be caused by the AoA failure?
https://hackaday.com/2019/03/14/mcas...-consequences/

So instead of pitot issue AND AoA issue we are back to all being caused by a bad alpha vane?
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Old 16th Mar 2019, 20:42
  #1640 (permalink)  
 
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Originally Posted by cockpitvisit View Post
Question from an SLF: Is it normal that you can trim an aircraft so far that you could not counteract the trim with the yoke, or is it a special feature of the 737?

What's the point of having a trim range exceeding the elevator authority? Are there any situations where this is needed?
That's essentially a function of pitch moment range (i.e. the extremes of nose-up and nose-down pitch moment), elevator effectiveness across the relevant speed range, and elevator force required to achieve full displacement throughout the speed range. As has been discussed ad nauseam, the pitch moment range in the 737 has expanded significantly as the engines have become more powerful and the thrust arm has lengthened (larger engines, thrust arm moved further below CG). Add to that the effect of moving the now quite impressively sized engine nacelles further forward just so they'll fit, which has the effect of reducing dynamic pitch stability in a high AoA situation, and you absolutely have the potential to find yourself in an area of the envelope where elevator control alone is not sufficient, particularly when you take into account the force required to move the elevator at high speeds.

As you've alluded to, the above is not an ideal situation, and one of the many reasons why it's not a good idea to hang on to common type certification by the skin of your teeth as you redesign an aircraft to within an inch of what's 'acceptable'. Now we'll likely see 'what's acceptable' being pulled back into line, leaving the 737 MAX sitting out there on it's own, essentially uncertifiable in it's current state. No doubt a quick fix will be rustled up, but it obviously won't fix the underlying issues.
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