Ethiopian Airlines Crash/ B737MAX grounding

troyzer

OSI wrote: »

So apparently they've replicated the Lion Air flight in a sim and found the pilots effectively had 40 seconds to discover the root cause of their issue and fix it.

Is that a lot? I have no idea.

murphaph

troyzer wrote: »

Is that a lot? I have no idea.

I would say it is not a lot at all. As I posted previously, Boeing gave the flight crews of that flight no chance. It's 40 seconds while desperately trying to pull the stick back in a doomed effort to fight against the MCAS trimming the stab. It's disgraceful this whole business.

odyssey06

murphaph wrote: »

I would say it is not a lot at all. As I posted previously, Boeing gave the flight crews of that flight no chance. It's 40 seconds while desperately trying to pull the stick back in a doomed effort to fight against the MCAS trimming the stab. It's disgraceful this whole business.

It might have been enough if they'd put it into the flight manual.

Nijmegen

I go back to an earlier point I made re US 1549 - Some (but not all) post-accident sims got the aircraft back to the field when they turned immediately after the simulated bird strike. But when they introduced a 35 second delay for real world figuring out status and options, they ended up dead. 40 seconds is not a lot of time to go from normal takeoff to -> unknown deadly things happening -> resolving the problem while you're fighting with the stick and trying to interpret alarms.

Raging_Ninja

OSI wrote: »

So apparently they've replicated the Lion Air flight in a sim and found the pilots effectively had 40 seconds to discover the root cause of their issue and fix it.



https://www.nytimes.com/2019/03/25/business/boeing-simulation-error.html

Well that's not necessarily accurate. The "40 seconds" was only reproduced if the pilots didn't press the electric stabilizer trim thumbswitch on the control yoke to override MCAS. The Lion Air pilots pressed it 24+ times, buying themselves a few-second reprieve each time before MCAS kicked in again.

bryangiggsy

Raging_Ninja wrote: »

Well that's not necessarily accurate. The "40 seconds" was only reproduced if the pilots didn't press the electric stabilizer trim thumbswitch on the control yoke to override MCAS. The Lion Air pilots pressed it 24+ times, buying themselves a few-second reprieve each time before MCAS kicked in again.

Can MCAS be turned off all together in flight?

Raging_Ninja

bryangiggsy wrote: »

Can MCAS be turned off all together in flight?

Yup, if you know how to which - since Boeing didn't tell anyone about it in their training documentation - few people did at the time of the Lion Air crash.

What documentation was released about MCAS prior to the Lion Air crash understated the effect it would have - Boeing claimed it could move the horizontal stabilizer by 0.6 degrees when in fact it was 2.5 degrees.

ZiabR

Raging_Ninja wrote: »

Yup, if you know how to which - since Boeing didn't tell anyone about it in their training documentation - few people did at the time of the Lion Air crash.

What documentation was released about MCAS at that point understated the effect it would have - Boeing claimed it could move the horizontal stabilizer by 0.6 degrees when in fact it was 2.5 degrees.

My understanding of the MCAS is that even when a pilot bypasses it, the software is still running in the background so MCAS is never fully off.

murphaph

Raging_Ninja wrote: »

Yup, if you know how to which - since Boeing didn't tell anyone about it in their training documentation - few people did at the time of the Lion Air crash.

What documentation was released about MCAS prior to the Lion Air crash understated the effect it would have - Boeing claimed it could move the horizontal stabilizer by 0.6 degrees when in fact it was 2.5 degrees.

2.5 degrees per activation. It activated multiple times on Lion air flight.

cnocbui

ZiabR wrote: »

My understanding of the MCAS is that even when a pilot bypasses it, the software is still running in the background so MCAS is never fully off.

No, MCAS is off if you engage the Autopilot or deploy the flaps. It is only active with manual control where the flaps are up.

billy few mates

L1011 wrote: »

Safer again would be 3+ AoA sensors and voting to exclude info from a faulty one, as is done on Airbus aircraft.

Plenty of duplex flight control/auto pilot systems that operate with voting systems that work with just two sensors. Normal protocol would be to monitor and disconnect in the case of exceeding pre determined value difference or in the case of slight differences within tolerance the system will always obey the sensor or input signal that tells it to do the least.
This problem could be easily resolved with a bit of additional crew training for familiarity and awareness, an alert to advise the crew when MCAS is active or operating, AOA vane position indicator and disagree warning and dual AOA sensor input into the system.

Nijmegen

cnocbui wrote: »

No, MCAS is off if you engage the Autopilot or deploy the flaps. It is only active with manual control where the flaps are up.

Autopilot won't engage when you're in a stall (or the plane thinks it is). Also, there should just be a cutoff rather than having to change the a/c configuration as a workaround. But then I suppose the next story about the MAX could be all the actual stalls occurring without MCAS because of the fundamental design of the plane, causing incidents and crashes. Goes back to the basic design flaw issue with it.

Bob24

cnocbui wrote: »

No, MCAS is off if you engage the Autopilot or deploy the flaps. It is only active with manual control where the flaps are up.

Can autopilot be engaged when the plane thinks it’s in a stall? And if autopilot had been engaged in the situations that let to the 2 crashes, would the computer not have been fed the same incorrect data by the faulty sensor and crashed the plane as well? (Maybe not, I genuinely don’t know)

billy few mates

Bob24 wrote: »

Can autopilot be engaged when the plane thinks it’s in a stall? And if autopilot had been engaged in the situations that let to the 2 crashes, would the computer not have been fed the same incorrect data by the faulty sensor and crashed the plane as well? (Maybe not, I genuinely don’t know)

No, MCAS is not active if autopilot engaged.
When the autopilot is engaged the the operation of the stab trim would be normal and expected as the autopilot stab trim servo trims the aircraft.
I think the issue here was the crews may have mistaken the operation of the stab trim (through MCAS) in manual flight as a stab trim runaway, particularly if they were unaware of the system or unfamiliar with its operation.

plodder

Nijmegen wrote: »

Autopilot won't engage when you're in a stall (or the plane thinks it is). Also, there should just be a cutoff rather than having to change the a/c configuration as a workaround. But then I suppose the next story about the MAX could be all the actual stalls occurring without MCAS because of the fundamental design of the plane, causing incidents and crashes. Goes back to the basic design flaw issue with it.

But, is it actually a design flaw, or just a case of differing flight characteristics that would need additional training to deal with? Is it not the case that all aircraft with low slung jet engines have a similar tendency to pitch up with power? Why would that not be considered a design flaw too? Genuine question btw. I don't know the answer.

Cloudio9

plodder wrote: »

But, is it actually a design flaw, or just a case of differing flight characteristics that would need additional training to deal with? Is it not the case that all aircraft with low slung jet engines have a similar tendency to pitch up with power? Why would that not be considered a design flaw too? Genuine question btw. I don't know the answer.

They wanted it to fly like the old 737 in order to avoid additional training for every pilot.

Nijmegen

plodder wrote: »

But, is it actually a design flaw, or just a case of differing flight characteristics that would need additional training to deal with? Is it not the case that all aircraft with low slung jet engines have a similar tendency to pitch up with power? Why would that not be considered a design flaw too? Genuine question btw. I don't know the answer.

Well the entire point of the MCAS was to ensure pilots wouldn't need additional training so that they wouldn't need a new type cert, and on the basis of needing a same type cert the engine placement/design is a flaw. I'd say it's also a flaw in that some platforms are just more stable than others and like to fly better, and for safe commercial ops you ideally want the most stable platform you can get. The 737 through its iterations has become arguably less stable as a platform and you could call that a flaw.

I think all this circles back to a real and genuine need to go clean sheet on the design given the requirements now put upon it for range.

ZiabR

plodder wrote: »

But, is it actually a design flaw, or just a case of differing flight characteristics that would need additional training to deal with? Is it not the case that all aircraft with low slung jet engines have a similar tendency to pitch up with power? Why would that not be considered a design flaw too? Genuine question btw. I don't know the answer.

We are not just looking at low slung bigger engines though. That was only part of the modification. They had to shift the engines forward aswell to make sure they cleared the ground. So bringing the engines forward and increasing their size results in changes to aerodynamics and the general balance of the plane.

They shoe-horned these customisations onto an age old design instead of redesigning from scratch. They took shortcuts to 1) speed up manufacturing, 2) save massive amounts on costs and 3) to push new aircraft to the customers faster so that they wouldnt potentially lose business to Airbus.

Then you have the whole certification calamity with the FAA where they again didn't do their job right and signed off on a new system that the majority of pilots knew nothing about.

Its one big mess.

Man Vs ManUre

I don’t think the average passenger would be willing to fly on this plane knowing if this sensor/system fail happened, that pilot knows to fly manual out of the problem even though plane may have already started moving erratically. Even if it was only couple of seconds of nose down erratic movement. Any deviation from smooth flight, even when only turbulence, is very scary for most passengers. I can’t imagine how I would feel if it went nose down.
Anyway Boeing say they have a software fix, but probably still a long journey to get this model flying again.
It really is criminal that they put this plane in the skies.

bryangiggsy

Man Vs ManUre wrote: »

I don’t think the average passenger would be willing to fly on this plane knowing if this sensor/system fail happened, that pilot knows to fly manual out of the problem even though plane may have already started moving erratically. Even if it was only couple of seconds of nose down erratic movement. Any deviation from smooth flight, even when only turbulence, is very scary for most passengers. I can’t imagine how I would feel if it went nose down.
Anyway Boeing say they have a software fix, but probably still a long journey to get this model flying again.
It really is criminal that they put this plane in the skies.

I wont be flying on any Max 8's for a couple of years as a result of this ....2 planes out of 350 is far too high imo ..... 40 secs to react....and to read a manual in this time....bonkers.

plodder

ZiabR wrote: »

We are not just looking at low slung bigger engines though. That was only part of the modification. They had to shift the engines forward aswell to make sure they cleared the ground. So bringing the engines forward and increasing their size results in changes to aerodynamics and the general balance of the plane.

I've seen a comparison of the MAX overlaid with the NG and the difference is pretty small. And from what I read, it's more the design of the nacelle that generates the unexpected lift rather than the position of the engines.

Also the engines on the MAX are closer to the wing. Maybe that reduces the under-slung effect and the tendency to pitch up in that context....?

They shoe-horned these customisations onto an age old design instead of redesigning from scratch. They took shortcuts to 1) speed up manufacturing, 2) save massive amounts on costs and 3) to push new aircraft to the customers faster so that they wouldnt potentially lose business to Airbus.

The above narrative is what we're reading from the media (fed by who I wonder?) - not from any official report or investigation.

Then you have the whole certification calamity with the FAA where they again didn't do their job right and signed off on a new system that the majority of pilots knew nothing about.

That is pretty alarming all right, and there was no reasonable justification for it. But, really that should be possible to overcome. I've an open mind on this bigger question on whether the design itself is flawed. I'm sure there will be politics when it comes to EASA and the Chinese giving it the thumbs up, but if they do, I'll be happy to fly in it.

Bob24

billy few mates wrote: »

No, MCAS is not active if autopilot engaged.
When the autopilot is engaged the the operation of the stab trim would be normal and expected as the autopilot stab trim servo trims the aircraft.

And the sensor which feeds MCAS is not feeding anything to the autopilot? (I honestly don’t know, but I would have assumed the autopilot might also take the current angle of attack as an input parameter and possibly make decisions based on it?).

Hotblack Desiato

ZiabR wrote: »

My understanding of the MCAS is that even when a pilot bypasses it, the software is still running in the background so MCAS is never fully off.

Nope, there's two switches to disable the electric trim motor, flip those and MCAS can't do anything.

billy few mates wrote: »

I think the issue here was the crews may have mistaken the operation of the stab trim (through MCAS) in manual flight as a stab trim runaway, particularly if they were unaware of the system or unfamiliar with its operation.

The action would be the same though - flip the two switches and trim manually.

billy few mates

Hotblack Desiato wrote: »

The action would be the same though - flip the two switches and trim manually.

I know, that's what I said earlier...

Tenger

plodder wrote: »

............
The above narrative is what we're reading from the media (fed by who I wonder?) - not from any official report or investigation.
..............

To be fair I read a similar opini9n on the B737MAX programmer about 3-4 years ago. It make the same points without the drama of the recent media reports:
‘A stretch too far’, ‘Boeing doubles down on the venerable B737 and abandons it’s MoM concept’, ‘Boeing is reacting with alarm to the surge 8n Airbus orders’

brendanwalsh

I wonder how many other planes have nearly crashed.

Boeing will be seriously hammered financially by this. Disgraceful.

Pronto63

Watch Primetime on RTE 1 tonight.

billy few mates

Bob24 wrote: »

And the sensor which feeds MCAS is not feeding anything to the autopilot? (I honestly don’t know, but I would have assumed the autopilot might also take the current angle of attack as an input parameter and possibly make decisions based on it?).

The AOA sensors normally just feed angle of attack into the Stall Management Computers (classic) or Stall Management yaw damper computers (NG) for stall warning, when they fail they fail passively (ie they don't cause any adverse effects), you normally only know they fail if the light comes on for a heater failure or the stall warning system fails to test.
The stall management system normally only has authority over the elevators (through the stick push system) in a stall condition, you can override that by pulling back on the stick.
MCAS acts directly on the stabiliser rather than the elevators, in certain circumstances the elevators may not have enough authority over the elevators to recover the situation.
The 737 also has a neutral shift system where the stabiliser moves to fair the elevator anytime the elevator is out of the neutral position, that could explain the flight profile in the last few minutes of the flight as the crew tried to battle the effects of MCAS (which they supposedly knew nothing about) with their own control column inputs, counter trim and neutral shift.

vicwatson

L1011 wrote: »

Chinese orders are made for political reasons tbh.

So what?

gctest50

L1011 wrote: »

Safer again would be 3+ AoA sensors and voting to exclude info from a faulty one, as is done on Airbus aircraft.

lol no

An occurrence was reported where an Airbus A321 aeroplane encountered a blockage of two Angle Of Attack (AOA) probes during climb, leading to activation of the Alpha Protection (Alpha Prot) while the Mach number increased. The flight crew managed to regain full control and the flight landed uneventfully.


When Alpha Prot is activated due to blocked AOA probes, the flight control laws order a continuous nose down pitch rate that, in a worst case scenario,

cannot be stopped with backward sidestick inputs, even in the full backward position.

If the Mach number increases during a nose down order, the AOA value of the Alpha Prot will continue to decrease.
As a result, the flight control laws will continue to order a nose down pitch rate, even if the speed is above minimum selectable speed, known as VLS.

This condition, if not corrected, could result in loss of control of the aeroplane