[Closed] This 737 MAX thing...

Maybe possibly perhaps.

As truth got the black boxes they'll know fairly quickly I suspect.
It seems the engines are further forward than normal on this plane and the anti stall system may be there to overcome inherent stability issues caused by the engine positioning.

It'll be on Air Crash Investigations before long. Until then, I'm not buying any of the largely irresponsible speculation that the media invariably go through with disasters like this, they only add to the confusion.

Every single time a plane goes down, people expect answers immediately and it simply doesn't work that way. Could take months to get a definitive answer.

Apparently they have two angle-of-attack sensors. If one misbehaves, the avionics can't decide if the plane is stalling or flying normally, so it pushes the nose down to conteract the perceived stall, then pulls it up again to maintain altitude, putting the plane into a roller-coaster ride. Great way to terrify the hell out of everyone before you finally fly them into the ground.

There's a lot of (relatively well informed) speculation on the PPRuNe forum.

https://www.pprune.org/rumours-news/619272-ethiopian-airliner-down-africa.html

I wouldn't get on one at the moment.

Two of the same models of a new aeroplane - both times pilot requested to return to land because of technical difficulties - crashing 6 and a half minutes after take off ... would be difficult to imagine anything other than design fault with aeroplane.

RyanAir start flying theirs at end of this month I read ... we fly to Gran Canaria 30th March!!

But apparently Boeing are about to issue a software update for the anti-stall issue!!

Amazing how much can be fixed by a bit of software!!

Can Boeing issueing a software update to fix the issue be seen as an admission of guilt?

Well the cause of the first crash was understood and Boeing issued guidelines as to how pilots can identify and deal with the issue safely so the question is did the pilot in this case follow those guidelines. Is so why didn’t they work, if not why not. This is assuming of course it is a common cause for the crash.

Can Boeing issueing a software update to fix the issue be seen as an admission of guilt?

Not really. Issues with the anti-stall stuff came out a good while ago and a directive was issued to tell pilots how to deal with it if it goes wonky. OTOH, it doesn't sound like they did a great job communicating this with customers before the Lion Air crash

Lots of interesting info in that pprune post (thanks for the link, Crazy Legs), sounds like a new captain and very inexperienced co-pilot - if it IS the speculated AOA sensor causing MCAS to engage, then MCAS applies more nose-down trim than both pilots can manually overcome at a point in the flight where they have no time or room to think.

This isn't pretty, considering Addis Ababa airport is at 7625ft

Communication with customers about actions to take don’t come from Boeiong or the manufacturer. They come from the airworthiness authorities. No excuse for an airline not to notice or act on an AD that is issued. It’s solely the airlines responsibility.

I wouldn’t get on one at the moment.

Me neither!

But apparently Boeing are about to issue a software update for the anti-stall issue!!
Amazing how much can be fixed by a bit of software!!

Better than sending out a note telling them there's an off switch for the anti-stall, which is what they did when they realised the problem (and blame it on pilots not realising how it works).

if it IS the speculated AOA sensor causing MCAS to engage, then MCAS applies more nose-down trim than both pilots can manually overcome at a point in the flight where they have no time or room to think.

That's why pilots have been issued with instructions on how to disengage the system. The whole point of the stick pusher is to get the nose down to increase airspeed so intended the pilots can't override until it is safe to do so, therefor they would need to disengage the system before the stick pusher system kicked in.

IF it is this issue repeating then there are a lot of questions....what set of circumstances need to occur to get the aircraft into this configuration or state and if that can be avoided by the pilots? If this issue does crop up, how long do pilots have to recognise it and disengage the system? In this latest case did everything behave as they anticipated or did something different (new) happen in this case?

If there was a proper issue that Boeing didn't have a solution for then the FAA and EASA would be grounding the global fleet...this has happened before i.e. fleets being grounded. So clearly on the basis the global fleet has not been grounded suggests Boeing has a solution for the issue...and knowing the airworthiness authorities as I do....they would have to be able to demonstrate they have a safe solution to dealing with the issue if it occurs...AND have a permeant fix and a plan to get that permanent fix rolled into the fleet in an acceptable timeframe. The question then becomes why didn't these pilots adhere to the instructions?

Similar situation to the Air France crash off Brazil. There was a known issue with Pitot tube freezing...the fix was in the process of being rolled out into the fleet and in the meantime pilots had been trained to recognise the issue and deal with it...in the AF case the pilots simply ceased to function...they became confused, didn't follow the most basic procedures and processes let alone recognise the specific issue, with disastrous consequences. So it was a human factors issue pure and simple. The pilots simply not doing their job.

Better than sending out a note telling them there’s an off switch for the anti-stall, which is what they did when they realised the problem (and blame it on pilots not realising how it works).

This is so much b'locks from someone who clearly doesn't understand how the industry works.

So it was a human factors issue pure and simple. The pilots simply not doing their job.

Accident investigation summary from 1978.

All of the above. Anybody who is familiar with the 737 will know that the engines already hang so low that they had to flatten the bottoms of the nacelles, so in fitting the bigger engine they had to move it up, which meant moving it forward to clear the wing, which changes the centre of thrust relative to the airframe. A flying instructor told me yesterday that the Max already has a bad reputation for tail-strikes, being as they have lengthened the fuselage. The same instructor also says to me frequently: "Behind every air crash there's an idiot".

Is this the aviation equivalent of a chipped BMW with a body kit?

Accident investigation summary from 1978.

+1

Root cause is still the tubes freezing over, not the pilots being unable to handle the situation. That is a contributing factor, the actual underlying contributing factor would have been more like the pilots training though.

The most insane thing from that crash was that modern airliners don't have angle of attack displays according to the telegraph and Der Spiegel.

If this issue does crop up, how long do pilots have to recognise it and disengage the system?

In this and the Lion Air incident, I think the answer is "not long" (unlike AF447). I think (if it's AOA/MCAS) the problem is when it occurs - they're so busy not crashing they don't have time to think about what's trying to make it crash.

I've always been surprised that nobody's invented an alternative to pitot tubes. Given their vulnerability to freezing, wouldn't it make sense to use two pitot tubes plus a completely different kind of instrument and compare the three readings? Surely, if one pitot tube ices up, the likelihood of others having the same problem will be fairly high.

https://www.pprune.org/tech-log/539756-af-447-thread-no-12-a-76.html

Lots of interesting snippets of info in there

AoA. How difficult and expensive can it be to display a computed AoA parasite from the computer?

"...ERM, FORTY DEGREES AoA....!?!!...Push the Nose Down, EH?"

Airbus was granted a waiver for no pusher/shaker at certification... They had convinced the authority that the a/c would not Stall in Normal Law, and in ALTERNATE, the pilots would be ready for STALL, no passive safety device would be necessary?

Additional design deficiencies.

1. Automatic Pitch Trim Nose UP into the STALL.

2. Absence of alerting device to signify Auto TRIM into STALL.

2a. Cumbersome manipulation of TRIM by hand, to return TRIM to neutral. Once released, the TRIM moves to regain full Nose UP. Extremely inconvenient in an emergency. Enforced distraction.

3. Surprise handling change in ROLL, splitting the stick into two modes.

4. Back up Speed System not installed, optional.

5. Low Energy Alerting Program not installed, not available.

6. Slow rolling replacements of deficient speed sensors, Pitots.

Then back in 2006, before the crash "Do we need AoA indicators".

https://www.pprune.org/tech-log/237364-angle-attack-indicators-do-we-need-them.html

The general theme for me, seems to be that aviation manufacturers have been trying to take as much responsibility away from pilots as possible - even removing passive safety systems such as pushers/shakers and AoA indicators (they argue that AoA indicators might cause risky behavior). But then when it all goes tits up because their wonderful automated systems fail, the pilots - unused to flying by the seat of their pants and without the right equipment to do it as easily as they could....fly the plane into the ground.

And we are supposed to be surprised, how?

All of the above. Anybody who is familiar with the 737 will know that the engines already hang so low that they had to flatten the bottoms of the nacelles, so in fitting the bigger engine they had to move it up, which meant moving it forward to clear the wing, which changes the centre of thrust relative to the airframe

Interesting chap on Radio 4 this morning, former BA pilot and now crash / safety consultant. He was 100% clear all aircraft should be grounded. He described the same issue with weight and position of engines making aircraft inherently unstable. The most incredible thing though was that, according to him, pilot conversion training for the Max 8 involves only a 90 minutes tutorial on an iPad!

Interesting chap on Radio 4 this morning, former BA pilot and now crash / safety consultant. He was 100% clear all aircraft should be grounded. He described the same issue with weight and position of engines making aircraft inherently unstable. The most incredible thing though was that, according to him, pilot conversion training for the Max 8 involves only a 90 minutes tutorial on an iPad!

It's overconfidence in technology, I see this with the "tech bros" in the computing industry that I hang out with.

Imagine the hilarity that would ensue and the uproar in the RAF if BAe took the AoA indicator out of a Typhoon - because...lol...fly by wire. You can't stall it so you don't need it brah, **** redundancy and giving pilots basic flight information!

pilot conversion training for the Max 8 involves only a 90 minutes tutorial on an iPad!

Better to use MS Windows surely, much more crash prone.

This is so much b’locks from someone who clearly doesn’t understand how the industry works.

Thanks . I clearly wandered into an aviation expert forum rather than a mountain bike forum where people spout b'locks. Yeah, sure I do. That's where we benefit from experts to correct us.

I think the thing here is that flying is staggeringly safe. The industry led the way in adopting a culture of safety, if you are interested in this have a read of Black Box Thinking. It is incredibly unusual for commercial planes to crash and there are very good systems in place to understand why they do and quickly take measures to apply lessons/changes/recalls/modifications to prevent the same from happening. The fact that two near brand new aircraft have crashed is a major red flag. It simply shouldn't happen and that is what is freaking out the professionals.

I'm amazed that all aircraft haven't been grounded, I wouldn't be surprised to see more airlines grounding throughout the day until none are flying.

Thanks . I clearly wandered into an aviation expert forum rather than a mountain bike forum where people spout b’locks. Yeah, sure I do. That’s where we benefit from experts to correct us.

The person who accused you of spouting bollocks, and then blaming it squarely on the pilots was bollocks as well.

High and forwards you say.....

Well, Boeing do seem to be gaining a similar reputation for dropping out the sky as Russian aircraft.

The most incredible thing though was that, according to him, pilot conversion training for the Max 8 involves only a 90 minutes tutorial on an iPad!

There's the issue then. Clearly they didn't use Drac's.

Airbus was granted a waiver for no pusher/shaker at certification… They had convinced the authority that the a/c would not Stall in Normal Law, and in ALTERNATE, the pilots would be ready for STALL, no passive safety device would be necessary?

There's a big difference - the Airbus relies on a voted source from three angle of attack vanes, the 737 has two. There was, interestingly, an engineering bulletin describing how the Airbus could do a similar thing to this due to two identically damaged or frozen AoA indications, and all Airbus pilots know exactly which two buttons to push to drop the aircraft into alternate law (ie without protections). This has been fixed for a couple of years now.

Also, an Airbus can stall in normal law if subject to violent enough environmental changes, but will fly its own recovery.

This is the problem - the training and conversion. The Max has been sold as being almost directly interchangeable with the 737-8 and most of the 500-800 range. As such, one of the biggest selling points to airlines was the ease of pilot training, swapping the max for older NGs. The problem was/is/might-be that the updated training and aircraft documentation did NOT include information on the anti-stall, auto control present on the MAX. Thus, the pilots are trying to gain altitude at a certain thrust rating and attempt to raise the nose as they would have on an NG, The aircraft believes (possibly due to sensor damage) that there isn't enough airspeed to maintain the manoeuvre and attempts to pitch the nose down to maintain what airspeed it has. The aircraft will continue to use its on-board sensors to override the pilots inputs right up to the point that it crashes into something as it has limited knowledge of the surrounding terrain and noting that would disable the anti-stall in respect of that terrain.

Also, an Airbus can stall in normal law if subject to violent enough environmental changes, but will fly its own recovery.

As will most aircraft, given enough height to play with!
Do they actually know the exact cause of the Lion Air flight crash - is there a report anywhere on it? A quick search has thrown up a whole load of added links to the Ethiopia flight now so it's got all muddled...

The aircraft will continue to use its on-board sensors to override the pilots inputs right up to the point that it crashes into something as it has limited knowledge of the surrounding terrain and noting that would disable the anti-stall in respect of that terrain.

That's a really interesting one that - if you end up stalling (somehow) and the aircraft is trying to pitch nose down to gain speed but the terrain avoidance system is calling Terrain! Pull Up! then which system wins?

the terrain wins

The aircraft will continue to use its on-board sensors to override the pilots inputs right up to the point that it crashes into something

But how the shuddering **** has this been released as a production aircraft without *someone* thinking that perhaps the input from the altimeter might be a useful thing to consider? There's an instrument right there saying "you're 100m away from crashing", and yet the software still continues to push the nose down?!

Crikey I am going to avoid flying in Boeing 737 MAX for now.

Better stick to A300 and A320 until they get it fixed.

The system will not pull-up to avoid terrain, that requires a pilot input and that's what the pilots were likely trying to do, but unless they understand that it's an intentional system that's causing the aircraft to nose-down, they will not be looking for that system to disable. they'll be looking for and trying to determine what failure is causing it.

We're well into speculation territory here, but, if the anti stall is pushing down, it is no longer working as intended.

There is a preliminary report on Lion air.

But how the shuddering **** has this been released as a production aircraft without *someone* thinking that perhaps the input from the altimeter might be a useful thing to consider? There’s an instrument right there saying “you’re 100m away from crashing”, and yet the software still continues to push the nose down?!

The GPWS and TAWS systems are there to provide that (altitude + terrain) information to the pilot in terms of a series of audible warnings. These systems can be used to auto land an aircraft, but often only at airports with local GPS correction and only on aircarft so equipped (A320 etc). the systems isn't automated as it's usually not required to be automated, the warnings are there for landing which is well planned and has energy/margin to correct.

Automation of the antistall is somewhat more critical. If not automated, it's surprisingly easy to keep nosing up and to stall the airflow on the wing and starve the engines of air. This essentially reduces energy on the aircraft to zero (ignoring potential) and the aircraft falls from the sky until such time as airspeed increases and the wings again begin to deliver lift. During take-off there isn't time for this, the plane crashes first.

I think - may be wrong - the anti-stall on the MAX is off when flaps are deployed, i.e. during take off.

We’re well into speculation territory here, but, if the anti stall is pushing down, it is no longer working as intended.

There is a preliminary report on Lion air.

Agreed.

It's not pushing down per-say, but it's preventing pulling up as that would reduce the airspeed.

incidentally, preliminary report for lion air

https://spectrum.ieee.org/riskfactor/aerospace/aviation/indonesias-safety-committee-releases-preliminary-report-into-lion-air-crash

I thought MACS was in use in all phases of flight after WOW release due to the inherent tendencies of the larger (more forward mounted) engined 737s to pitch-up after at higher angles of attack? The larger 737s have a limited rotation angle which (i thought) means they had to pitch slightly more aggressively after takeoff.

the inherent tendencies of the larger (more forward mounted) engined 737s to pitch-up after at higher angles of attack?

This part I don't understand. So they had to move the engines forward and upward to give ground clearance. That would move the center of gravity forward relative to the aerodynamic center of pressure, so the aircraft should tend to nose down. However, the newer models have also been stretched, plus aerodynamics have been revised, so surely all that should have been integrated to keep the aircraft stable when it's properly loaded. Unless Boeing really screwed the dog, of course.

Edit. Explained here. https://theaircurrent.com/aviation-safety/what-is-the-boeing-737-max-maneuvering-characteristics-augmentation-system-mcas-jt610/

Just announced UK has blocked the aircraft from flying over UK airspace.

Ignore me

It would appear that the vairous aviation authorities are effectively grounding the fleet. Which saves me from having to work out if I'm flying on one in the near future - and demanding a different flight.

Phew, two very similar appearing incidents in the first two years of operation does point to either a serious design flaw, a serious flaw in the conversion training of the air crews, or both.

Which saves me from having to work out if I’m flying on one in the near future – and demanding a different flight.

Yep, quite glad about that, as I'm flying next week...