Ethiopian airliner down in Africa

[FCeng84]

Originally Posted by CurtainTwitcher

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.

[CONSO]

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.

[brak]

Originally Posted by Rated De

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

[Rated De]

Originally Posted by brak

He's back at the FAA, in charge of safety.
https://www.ainonline.com/aviation-n...viation-safety

Revolving doors and all.....

[CurtainTwitcher]

Originally Posted by FCeng84

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.

[tartare]

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.

[Speed of Sound]

Originally Posted by atakacs

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.

[Recidivist]

I understand - what I was thinking of was not the complexities of flight as the pilot sees them, but purely focussing on the automation aspect - why allow an automatic system to operate the airplane when AoA and pitch gyro are indicating different things? Sure, it's possible both are correct, but the pilots are there to make those decisions. Why allow the automation to continue to pitch down when the altimeter is showing accelerating loss of height? A pilot may indeed do this to recover from a stall, but surely it would be rare to rely on autopilot to get you out of a stall?
I gather there are situations where the pilots are presented with a message that indications disagree, and the automatics effectively hand the matter over to the pilot - I'm just exploring why that isn't the case when to continue with the automatics could result in catastrophe.

Edit: Replying to predictorM9

[hunbet]

“Evidence we found on the ground made it even more likely that the flight path was very close to Lion Air’s,”

I suspect they located the stab trim jackscrew and could tell it's position.

Also :“The FAA is ordering the temporary grounding of Boeing 737 MAX aircraft operated by U.S. airlines or in U.S. territory. The agency made this decision as a result of the data gathering process and new evidence collected at the site and analyzed today. This evidence, together with newly refined satellite data available to FAA this morning, led to this decision," the FAA said.

[Matt48]

Originally Posted by weemonkey

'cos it's nothing more than a deep hole in the ground. That's why.

It's more than 'a deep hole in the ground', it's also full of potential evidence, have they recovered the stabiliser jack screw mechanism for instance, also ground witness reports smoke and debris issuing from plane before impact, all the bits need to be recovered, the whole site has been grossly mismanaged.

[jimtx]

Originally Posted by weemonkey

"The thrust line has changed from the NG because the engines had to be moved forward and up to accommodate the larger fan diameter. Any handling differences as a result of this have beentuned outby Boeing in the flight control system to make the types feel the same to crew. This was necessary for certification under the same type certificate."

From
Boeing 737 MAX - Differences

The handling differences due to thrust line may have been tuned out but it wasn't by MCAS. Windup turns are done with set thrust.

[mickjoebill]

Have we passed the point in modern aviation where it is not possible to (quickly) switch off all these pilot and performance aids and fly “manually”?

At very least, the last resort if flying in VFR conditions?


Mjb

[mm43]

Originally Posted by Speed of Sound

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.

I can't disagree. There is a perception that the two incidents being dealt with happened "elsewhere", and the importance of protecting the credibility of the FAA and Boeing is paramount
.
May be its time for the NTSB to assess what has led to this shambles.

[jimtx]

Originally Posted by FCeng84

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.

Just trying glean what flight regime MCAS needs to protect. So, they didn't want the column cutout switch to work because they envisioned pulling hard and not trimming. Trimming would normally return the column to neutral. Two things come to mind. Windshear escape in the clean config and steep turns with guys that don't trim. I (having the T-38 training mantra embedded, "trim trim trim") would trim during steep turns so that would not be a problem for me or MCAS. Of course steep turns are a simulator exercise so not really relevant. Again I ask why put out the original AD and not caution about being careful when pulling with the loss of MCAS.

[FIRESYSOK]

I think the satellite data *could* refer to any ACARS maintenance information transmitted to Boeing and/or GE and/or Ethiopian. Just like the AF accident, there were ample maintenance fault messages received well before the FDR was recovered that might have given the precipitation of events

Regarding the larger picture here, an average crew, newly aware of the newly-revised MCAS ‘warnings’ could still be easily saturated by stick-shaker, air data miscomps, and ever-increasing stick forces in that scenario.

Disconect stab trim trim, pitch and power for a safe climb-away...may have been too much for a crew of certain caliber. Simulator training may have mitigated an accident of an afflicted crew, but time will tell what went wrong, and how.

[predictorM9]

Originally Posted by Recidivist

I understand - what I was thinking of was not the complexities of flight as the pilot sees them, but purely focussing on the automation aspect - why allow an automatic system to operate the airplane when AoA and pitch gyro are indicating different things? Sure, it's possible both are correct, but the pilots are there to make those decisions. Why allow the automation to continue to pitch down when the altimeter is showing accelerating loss of height? A pilot may indeed do this to recover from a stall, but surely it would be rare to rely on autopilot to get you out of a stall?
I gather there are situations where the pilots are presented with a message that indications disagree, and the automatics effectively hand the matter over to the pilot - I'm just exploring why that isn't the case when to continue with the automatics could result in catastrophe.

Edit: Replying to predictorM9

For the AoA sensor and the pitch angle, these are not the same and so they disagree in general (the difference between the two is the angle of climb or descent, which is not always zero).
Even if you have an accelerating loss of height, you can not know if you are out of the stall or not, so the automation relies only on the measurement of the angle of attack to determine that. They don't reconciliate the data from all sensors to check what sensor is ok and what sensor is faulty, the logic to do that would be a bit complex and probably not certifiable.

[Trackmaster]

Originally Posted by tartare

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.

Well said. The grounding was inevitable and the delay just added to the reputation damage.

[positiverate20]

Originally Posted by FCeng84

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.

I agree with you on the sensor problem, but entirely disagree with the perception that a failure of the system would have minimal risk to the aircraft.

In the scenario given, hundreds of feet above ground, stick shaker, the captain is in a pretty tough situation and is trouble shooting- does stab memory item, switches stab cut-out. Alarms off, and thanks to yoke and increased thrust returns to some form of climb. At this stage, despite your argument that the pilot should be able to return trim to normal, he has just followed the procedures that Boeing themselves have instructed. Checklist complete, some stability back and now focus on safely trying to get back to ground.

Now, throughout this next phase, with the stab having X° nose down, it may not present itself as a problem due to the additional engine power, because, at increased thrust, as you've explained, the Max set-up has a tendency toward a higher AoA, which is why MCAS is required in the first place! So, in a sense, the characteristics of the MAX set-up will be masking the trim. MCAS is required for certification to counteract the increasing rotation around the CG caused by the both the thrust moment and aerodynamic behaviour of the engine cowling of the Max engine. So, in this precise stage of the hypothetical flight the PIC may not actually notice the plane being out of trim, and if he does, will surely not realise just how much out of trim he actually is. Any other time in normal MAX operation the autotrim or the MCAS trim would be operating anyway. MCAS, as you've said, is a certification requirement for MAX aircraft because of it's specific aerodynamic characteristics. What I'm portraying in this scenario is that if the pilot functioned perfectly during the emergency at 190, but in doing so cut-off the trim at X° nose down. That trim hasn't changed and the checklists didnt require the crew to make any manual trim wheel changes. By the time he actually realises how out of trim he is, he's doing 350, and despite the stab still being at the same X° nose down since cut-out, the forces have multiplied. Now if there is any nose down attitude or reduction in power then there's absolutely no chance to recover.

Obviously all hypothetical, an airspeed disagree on takeoff could lead to circumstances similarly, or a multitude of other possible reasons, however, in the situation that I've hypothesized, it would almost certainly always end in a similar steep nose down attitude.

[gums]

Salute MJB !!

On most airliners it is possible to fly "manually" with good training and practice/experience. Landings and takeoffs by the carbon-based life forms are good examples. Even then, many planes have pitch and yaw dampers to keep the planes really stable and predictable when not using the autopilot.
The Airbus that went down years ago over the Atlantic was a very stable and predictable aerodynamic machine. It handled so well that the crew flew it into a stall and did not realize that they had done so. Most pilots could prolly fly that type in the backup control laws with just a bit of practice.
The basic 737 used to be that way, but the basic design was modified time and again until it no longer exhibited the same aerodynamics as the one certified 40 or 50 years ago. Just look at a classic version and then the MAX. Who would think that the two shared the same original designation? Boeing added this and that to avoid an expensive "start over" cetrtification process, plus, the FAA allowed Boeing to "build upon" the existing certification. A new process/designation for the MAX would have not been allowed to add another kludge to preserve longitudibnal stability and handling requirements. The plane would have been required to demonstrate traditional control force and pitch moments at high AoA without the MCAS kludge.

A pure FBW control system has all the "protections" and limits/warnings and such as part of the basic design. But no FBW commercial airliner has failed to meet the basic aerodynamic requirements for stability and control if they all had ropes, levers, pulleys, cables, torque tubes, etc to move the ailerons, rudder and elevator. They are not the military or utility platforms and do not haul 200 folks about to visit aunt Clara.
So Boeing adds another thingie besides the STS speed stability doofer to meet Part 25 requirements and it gets signed off. Most of we pilots would handle the new thingie if and a BIG IF we knew it was added AND we were told what possibel failure indications existed AND we practiced a bit. GASP!! None of that was done.
My experience was in military planes and before each flight we had to sign off every little notice, directive and change and such before flying. On some mods we had to fly with an instructor before being cleared "solo". The MCAS mod required none of those things, and I have problems with not having seen a revolt by a thousand 737 pilots that only discovered MCAS after Lion 610 pranged.

'nuff bitching, and I close for now

Gums

[wrench1]

Interesting article:
https://www.theatlantic.com/notes/20...37-max/584791/