Boeing 737 Max8 Aircraft Crashes and Investigations [Part 3] 36

[Sparweb]

This is the continuation from:

thread815-445840
thread815-450258

This topic is broken into multiple threads due to the long length to be scrolled, and many images to load, creating long load times for some users and devices. If you are NEW to this discussion, please read the above threads prior to posting, to avoid rehashing old discussions.


Some key references:

Ethiopian CAA preliminary report

Indonesian National Transportation Safety Committee preliminary report

The Boeing 737 Technical Site

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[LionelHutz]

All 737's have an electric motor on the stabilizer so all of them could potentially suffer from a runaway trim event that drives the stabilizer to one extreme. It's silly of anyone to claim the manual trim system on the MAX must be built differently because it's the only variant that could suffer such a fate.

It's just a knee jerk reaction since the plane has suffered from trim runaway when that's something that almost never happens and something they generally aren't concerned about or do much training on. I'm doubting very many simulator sessions include trim runaway when there are so many other more likely to occur scenarios to use.

 

[Alistair_Heaton]

I think it's more because there is a system which generates input to the trim system which you have no indication when itsactive or not.

So before you had an extremely rare trim runaway event which you are correct is very rarely visited in the SIM. And now you have none pilot input to the system which if you don't spot something is wrong inside 5 seconds you have no chance of manually trimming it without doing some pretty hairy control inputs.

So either you give a method of killing the mcas without disabling the electric trim and give it enough power to do the job. Or you enable the ability with the manual trim. Or you get rid of the mcas.

 

[3DDave]

The FAA cleared a commercial pilot with 300 hours? That's where collusion investigations need to be focused.

Also, you have 9-10 seconds. At which time the yoke is pulling hard. And the PIC/PF pushes the trim switch button** until the trim is back to neutral before cutting out the trim motors. And the other pilot is pulling back the power and calling out both the trim and the pitch so the PIC/PF can deal with the controls. Isn't CRM taught anymore?

**Trim switch has higher priority and the main time problem is because of letting the speed get away from the pilots.

 

[LionelHutz]

I simply don't buy the claim that it must require a minimum of 8000 ft available to be able and manually trim a 737.

Of course, it could require dropping 8000 ft in altitude to manually trim a 737 depending on the flight conditions when you're attempting it. But, it likely shouldn't be attempted during those conditions.

 

[SwinnyGG]

I simply don't buy the claim that it must require a minimum of 8000 ft available to be able and manually trim a 737

That 8000 ft. number is based on a situation where the trim runaway has advanced unadressed for such a long time that:

1) control forces are too high for the pilots to manually trim using the wheels without maneuvering to reduce control forces

2) The elevator is so far out of trim that this procedure must be repeated many times to get the aircraft back into trim

The 8000 ft. scenario is the case where trim runaway starts, the pilots don't notice for many minutes, and finally realize they need to 'yo-yo' to re-trim.

In other words, 'it takes 8000 vertical feet to manually re-trim a 737' is not a wholly accurate statement. 'It may take 8000 vertical feet to re-trim a 737 under very specific conditions when a trim runaway or failure has gone unadressed for a long time' is more accurate.

 

[VEBill]

"...trim runaway....something that almost never happens..."

Unfortunately, it's happened several times in recent months.

 

[Alistair_Heaton]

I fly with pilots with 195 hours total. I presume under Ethiopian rules 300 is enough for a First officer cpl. Internationally you need 1500 hours and 500 hours multi crew to be an ATPL holder to be a Captain.

The test is not for a FAA license so the FAA will do the test.I believe the 1500 hour restriction in the us is only for commercial transport there is nothing stopping you getting the type rating on a ppl with less hours.

And you forget the stick shaker has gone off and triggered the stall recovery procedure which involves pitching the nose down which is going with the mcas trim change.

So give it 30 seconds Sully delay to figure out what the problem is and your dead. Have a separate warning that mcas is active and AoA mismatch and you might have a reasonable chance that your average crew will pick it up after undergoing SIM training. 45 mins on an iPad no chance.

Stick shaker is something that they are trained to act instantly for and it takes priority over egpws warnings. To get them to first check the trim system before recovery would be fighting against basic training.

As I said if you don't want the locals crashing the machines your going to have to design the machines to the local minimum standard of pilot. If you don't people die and your reputation gets trashed. If you don't want your reputation trashed don't sell them the machines.

Moaning the pilots didn't do the right thing you can get away with once. Two down in 6 months your stuffed.

 

[Alistair_Heaton]

https://youtu.be/rxPa9A-k2xY

Here is the screw Jack in action full range in 90 seconds.

 

[3DDave]

I'd think it trashes the airline's rep more.

In the case of ET302, the stall warning was with flaps extended and autopilot on, so no MCAS.

That was 90 seconds before they retracted the flaps, so triple Sully's time.

Soon after, the autopilot disengaged and 5 seconds later the first trim-down happened.

It moved down 2.4 units and they trimmed up .3 units. When it later trimmed down another 2 units, they interrupted it when they trimmed up 1.9 units, leaving them 2.2 units nose down from trim.

Which part of that is covered in training? That's when they decided to cut the power to the trim motors.

In roughly 3 minutes they never seem to have monitored airspeed which ran through Vmo.

I'm missing the quality that a commercial airline crew should have before an airline lets them in the front row seats.

Ethiopian Air has greatly expanded recently; I suspect the way they did that was to jettison the former standard of quality that they had.

 

[LionelHutz]

That 8000 ft. number is based on a situation where

It was based on a simulation of the Ethiopian flight where the plane speed exceeding Vmo and the throttles were left at 95% or whatever it was.

And you forget the stick shaker has gone off and triggered the stall recovery procedure which involves pitching the nose down which is going with the mcas trim change.

So give it 30 seconds Sully delay to figure out what the problem is and your dead. Have a separate warning that mcas is active and AoA mismatch and you might have a reasonable chance that your average crew will pick it up after undergoing SIM training. 45 mins on an iPad no chance.

Stick shaker is something that they are trained to act instantly for and it takes priority over egpws warnings. To get them to first check the trim system before recovery would be fighting against basic training.

There was minutes, something like 3 or 4, with the stick shaker going off. How long do the pilots need before determining that it's wrong and should be ignored?

Ask your 737 flying buddies how much runaway stabilizer training, which includes having to manually trim the plane, they have taken. Ask them if they sim train for it. I'm betting there is not much if any training since other failure scenarios are much more likely making them the ones that would get training priority.

Lack of trim runaway training, indicator or not, would be my guess as the root cause behind why the pilots couldn't recover from it.

 

[Alistair_Heaton]

You can't really get more trashed than Lion Air anyway.

The quality is hugely variable around the world.

You just have to look at the Colgan Air Flight 3407 which was a 1st world nation home grown crew. Didn't respond correctly to a stall warning which is definately is trained for.

You can't generate that number of pilots locally especially Captians. They have done it with expats mostly western with a few Saffas and some Kiwis and Auzzies. Two mates have just gone there to fly the Q400.

The strange thing for me is the AP stayed in when the stall warning triggered. It normally disconnects as soon as the stick shaker goes off.

We shall see, Boeings image is getting trashed by more than just the two crashes, that documentary is pretty good at rubing the salt into the raw wound. The FAA isn't looking good either. To behonest most of us in Europe think EASA is a bunch of lawyers and paper pushers without a clue and looked at the FAA as something we could only dream of. Now it seems they are as useless as our own regulators.


The stuff I have seen says it was likely a bird strike just after the gear came up. ASI mismatches, stick shakers and then the third issue with the MCAS. All crew will be able to deal with 1 issue most can deal with two if both are experenced on type and there is no rush to deal with them. Three issues will over load the majority of crews and become fatal.

We can all sit back and in hind sight say why didn't they do xyz.

I still think that the max will be flying in US airspace by about September/oct. Rest of the world earlest Jan/Feb 2020. If any of the others systems are deemed unacceptable for certification which is even chances then it could be into 2021.


you are correct its not part of the training cycle for the systems training. Our type rating syllabus has it in it for intial. Anyone that joins the company who already has a type rating if they haven't done it before they won't during induction.

 

[Alistair_Heaton]

https://www.aerotime.aero/clement.charpentreau/22670-no-boeing-737-max-for-the-summer?

 

[waross]

I remember a overhearing a construction foreman give his crew a morning pep talk;
"Be real careful out there today.
The Push is on and Safety's gone!"


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Alistair, Thank you for your explanation of the interaction between the flaps and the elevator trim.
I have seen a couple of times a reference to an instruction;
"Turn the trim switches off and leave them off for the remainder of the flight."
In this event, will the co-pilot be manually cranking the trim wheel as the pilot extends the flaps for landing?



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alistair_Heaton]

I don't know for the 737. If possible in the west we stick to one pilot flying and one monitoring. Unless it's physicaly impossible to not control the aircraft with just one. Russians it tends to be normal. In fact you can have two on the stick and the flight engineer on the power levers. This is historical due to russian design giving extremely heavy flight controls and the engine management being a full time job for one person. The old turbo props had 5 levers per engine and X that by 4 engines one person's hands weren't big enough to adjust them all symmetrically.

 

[waross]

All 737's have an electric motor on the stabilizer so all of them could potentially suffer from a runaway trim event that drives the stabilizer to one extreme. It's silly of anyone to claim the manual trim system on the MAX must be built differently because it's the only variant that could suffer such a fate.

I agree. But this raises an interesting point.
Is this another design flaw that slipped past the regulators?
For that reason there may be a lot of reluctance to make any changes to the hand-wheel trim hardware.
It may be seen as an admission that the original design was flawed and that the whole 737 fleet should be upgraded.
That is not going to happen is it?


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alistair_Heaton]

Once you know the aircraft the trim amount is instinctively set so if you flight idle from cruise to decend you know it's three spins of the wheel.

But automation removes this from a swept wing jet pilots contious actions. Turbo prop we adjust the power constantly ourselves. The jets the autothrottle is in and the fms controls the target speed and engine settings to minimise fuel burn depending on the cost index.

When people come onto the dash for command upgrade from the jets it can be rather traumatic for them loosing the autothrottle. Which maybe the reason why the power was left on in both the accidents. They are just used to flying with two hands on the stick and the aircraft looking after the power. Where us tp drivers it's definitely one hand on the stick and one on the power levers at all times while flying manually

 

[Alistair_Heaton]

It hasn't slipped through. Its a 1960's design when such details were not considered important. 50 years later lessons had been learnt and a different opinion is held. And to be fair it hasn't caused alot of fatalities until recently

But due grandfather rights it's never been required to modernise it's design or philosophy. The 777 and 787 certainly don't have this feature.

 

[LionelHutz]

The strange thing for me is the AP stayed in when the stall warning triggered. It normally disconnects as soon as the stick shaker goes off.

The pilot engaged the autopilot while the stick shaker was going off.

 

[Alistair_Heaton]

Normally you can't engage it with it running, you have to press the yoke disconnect button for 3 seconds which resets the system. Then with the stick shaker going, press the engage button again, it will then come up with mode inhibit on your PFD and it will stay out. This I believe is common on Honeywell EFIS fits.

http://www.737ng.co.uk/737-800 Quick Reference Handbook (QRH).pdf

There doesn't seem to be a spurious stick shaker QRH card either. If we have it going off we can kill the system by pushing the annunciator light. After doing the AP reset 3 seconds you can then engage it again. Which again seems weird because you really don't want it running while trying to land the aircraft, for noise and communication and for the annoyance of the stick waggling while you trying to land. Again I am pretty sure modern certification standards require you to be able to kill the system.