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kgwilson

Ethiopian 737-800 Max crash - No survivors

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Transition training to the Max 8 for existing 737 pilots.....56 minutes on an ipad.......

 

I thought modern aircraft systems, faults and alarms were monitored via satelite in real time to the aircraft mfg and operator? 

 

 

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The problem as I understand it is the massive fan diameter on the newer fuel efficient engines. The engines have to be positioned lower further from the centre of drag. This causes a pitch up when thrust is applied. 

 

The only clean sheet design that would eliminate this would be a high wing with under slung engines, the public would not like this.

 

The engines on the new 777-x have a similar diameter to the 737 fuselage. 

 

Only because it would look different. There are plenty of great high wing designs around. How about mounting the engines on top of the wing. Same issue. To my mind the current design has reached its limit. It is now the only aircraft with actual cables from the yoke & trim wheels to control surfaces. Side sticks, electronic yokes and FBW is the standard now but even with triple redundant systems things can still go wrong as in QF72 in 2008 when one of the 3 systems went haywire. The fact remains though that accidents have continued to decline since FBW has become the norm, the current 2 Max 8 disasters beginning a reversal of the trend.

 

 

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...It is now the only aircraft with actual cables from the yoke & trim wheels to control surfaces...

 

-a source of some comfort to me.

 

 

 

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It is now the only aircraft with actual cables from the yoke & trim wheels to control surfaces.

 

It's not the fact it has control cables, it's who or what controls them....

 

 

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It's now been revealed that the 737 MAX has 2 AoA sensors - but Boeing engineers in their wisdom, decided that only one was needed to drive the MCAS system. A complete lack of redundancy right there.

 

In the case of the Lion Air crash, it appears that particular AoA sensor was faulty, and feeding incorrect date to the MCAS. Lion Air maintenance apparently failed to pick up the faulty AoA sensor - perhaps because it was an intermittent fault.

 

It is increasingly likely that the Ethiopian crash was caused by identical reasons/conditions to the Lion Air crash - a single faulty AoA sensor, pilots unaware of how the MCAS responded or operated, and an unwillingness to hit the trim cutout switches, when the MCAS was constantly countering their efforts to bring the nose up.

 

There's also warnings that Boeing was left to carry out System Safety Analysis on the 737 MAX MCAS design, rather than having the FAA or another independent body carry out the SSA.

 

In this case, the flaws of internal corporate safety analysis, regarding potential safety problems, related to major design modifications, have been shown to be very large flaws.

 

https://news.slashdot.org/story/19/03/18/1730247/flawed-analysis-failed-oversight-how-boeing-faa-certified-the-suspect-737-max-flight-control-system

 

 

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In the case of the Lion Air crash, it appears that particular AoA sensor was faulty, and feeding incorrect date to the MCAS. Lion Air maintenance apparently failed to pick up the faulty AoA sensor - perhaps because it was an intermittent fault.

 

A new plane worth over 100 million and there's a fault with the AoA after 3 months..... so much for the certification process...and the prices these things cost.

 

I'm unsure if it was a new design but it reminds me of the Rotax fuel pump saga.

 

After 20 years of stellar service Rotax replaced the pierburg (sealed unit) fuel pump with a different type.(screws on cover)

 

Instantly there were issues with over pressurisation of the carby floats and high pressure alarms going off.

 

A local aircraft had to have it's 300 hr pump replaced recently as it started leaking oil out the drain.

 

I have no idea why a mfg would legitamately replace a pump that had proven itself over DECADES.

 

I can only think marketing had more "pull" than engineering and saw a super reliable part as a "bad" part because it didn't prematurely fail and make them money in spare parts.

 

Totally the opposite as to how and aircraft engine mfg should behave..... in the end, just greed. 

 

 

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It's now been revealed that the 737 MAX has 2 AoA sensors - but Boeing engineers in their wisdom, decided that only one was needed to drive the MCAS system

 

I'm not one to stand up for Boeing, but that would make it very easy to troubleshoot the system in the air, if you understand your systems. That's where the lack of training may be an issue.

 

A new plane worth over 100 million and there's a fault with the AoA after 3 months....

 

That could be as simple as the AoA probe being damaged by the uneducated stair and service truck operators, not necessarily a manufacturing fault.

 

Not suggesting that that is the problem, but a possibility.

 

 

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it appears that particular AoA sensor was faulty,

 

 

 

Sensors as simple as EGT, CHT, OT, OP are far from being fault free.  Because we're generally familiar with the way readings will run if there is a real problem, and the fact that say a high OT causes a low OP, it's possible to work it out. So, annoying - but no big safety risk.

 

However, when we get into the realm of attitude sensors, anything faulty can be catastrophic.  Hard to understand why manufacturers can't just fit a 2nd, even 3rd sensor into the setup, which could be defaulted to if the 1st sensor 'fails' or gives readings way outside a normal range.  There must be an electronic way to have these sensors be subject to 'self-test' after start-up, and the control systems default to the correct sensor?

 

Why Boeing even fitted MCAS is a mystery. After all, the Airbus was the make involved in the several serious accidents related to inadvertent airframe stalling and subsequent loss-of-control. Improved crew training seems to have resolved this.  It would appear that Boeing engineers had a very poor opinion of pilot capability, and tried to 2nd guess them?

 

 

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There's no mystery as to why Boeing fitted the MCAS. It was fitted to try and give the same "feel" to pilots and FO's, from the 737 MAX, as the earlier model 737, with the original engines. 

 

The fitment of the new engines unbalanced what was originally a balanced design, and as a result, Boeing felt the need to restore the original models mild handling. 

 

It became obvious in testing of the 737 MAX that the new engines could upset aircraft response in some rapid pitch-up situations, because the nacelles were providing additional, unexpected lift, and interfering with airflow over the wing above the engine.

 

So, in came Boeings answer, the MCAS, to reverse any unexpected additional pitch-up caused by the new engines.

 

Kind of like fitting automatic steering correction to the new re-engined, higher-powered, bike or car you just bought, to counter the oversteer caused by the massive additional power - but the manufacturer neglected to tell you the automatic steering correction was fitted, and told you even less about how it worked.

 

 

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This explains how it all happened. A lot to think about even if you only fly a simple aircraft. 

 

 

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So we can now expect a lawyer‘s picnic ascribing blame & costs to various parties, a software update, and re-wired integration of the second AoA sensor into the flight control system & related algorithms.

 

How sad that this post-crash detail wasn’t better promulgated & rectified after the first Lion Air crash. Must investigations really take so long to deliver preliminary findings...?  If it was dealt with sooner, might it have prevented the Ethiopian crash?  Might we blame lawyers for this delay in releasing findings?

 

As so often seems to be the case, the cause of these tragedies could also be shared across a number of groups (Boeing accountants, engineers (software & hardware), airline crew training staff, airline maintenance procedures, FAA regulators vs. corporate expediency, and lastly, flight crew experience & expertise, (though it seems they weren’t really given all relevant info & training to rectify this issue).

 

My condolences to the families of all the victims from these crashes.  Blame and lawsuits won’t bring the victims back to their families. The only positives will come from complete transparency about the why’s & how’s of these crashes - and an undertaking to not repeat the mistakes.

 

 

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There's two  bit of info I hadn't seen before: that the MCAS system, as well as adjusting the trim, puts the engines to full throttle. And also that it is not armed until the flaps are up.

 

 

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I have to say I'm a bit confused about the full throttle comment, as both this commentator and an earlier one at post #54 have stressed this may result in nose-up pitch. In fact, the first Video at #54 has the commentator in a simulator stressing that point and increasing power very carefully while recovering from a near-stall.

 

Not that this makes much difference to the fundamental problems with the system. But why would the MCAS system put the engines to full power at near-stall, if the effect of that is to pitch up???

 

 

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"Doomed Boeing Jets Lacked 2 Safety Features That Company Sold Only as Extras"

 

 

 

 

https://www.nytimes.com/2019/03/21/business/boeing-safety-features-charge.html

 

The guts of it:

 

"Boeing’s optional safety features, in part, could have helped the pilots detect any erroneous readings. One of the optional upgrades, the angle of attack indicator, displays the readings of the two sensors. The other, called a disagree light, is activated if those sensors are at odds with one another."

 

 

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Difficult to select optional instrumentation if nobody tells you the increased relevance of what it's monitoring?

 

And so the sorry tale continues to unravel.................(

 

 

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I'm sorry, but I can't see why an automated stall recovery is even needed.  Bitchin' Betty should be yelling "STALL STALL STALL" at the top of her voice, and any pilot who's been in any sort of aircraft would be pushing the nose down.

 

 

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The implication seems to be that in some circumstances getting the nose down would require not only elevator, but significant change of trim, more so than in the new model? And/or there is something especially ugly now about the stall or near-stall that they are fighting shy of?

 

One of the earlier links in this thread took a quite different tack, and explained the intention of the MCAS as being to generate increased 'pull' on the control column, so encouraging the pilot to ease it forward. I can't say I followed the logic of that, although in a genuine near-stall situation, that may well be one of the effects???

 

 

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It's not fully clear so far how the pilot operated trim interacts with this MCAS trim; we keep getting little  bits of new information (like the fact that the flaps disable the MCAS, and the suggestion that MCAS also affects engine settings).

 

We are told pilot trim temporarily halts the MCAS activity. We are not told if, during this MCAS halt, the pilot is able to trim back up, though given what we now know, I would guess not.

 

And we are not told if the pilot holding the trim switch constantly activated results in a continuous override of the MCAS, though again this seems unlikely, given events.

 

I would guess that MCAS is paused by the activation of the pilot trim switch, but that no up trim results.

 

And I would guess that when MCAS then resumes , a fresh activation of the pilot trim switch is required to pause it.

 

 

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There are also some reports indicating mcas was a normal operating function and others saying it was an emergency function.

 

Does it operate on every take off?

 

 

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One of the earlier links in this thread took a quite different tack, and explained the intention of the MCAS as being to generate increased 'pull' on the control column, so encouraging the pilot to ease it forward. I can't say I followed the logic of that, although in a genuine near-stall situation, that may well be one of the effects???

 

My understanding is that there is a certification requirement that as the AoA increases as the control column is  being pulled back, the pressure required on the control column should not decrease. 

 

For the MAX, the aerodynamic effect of the larger, more forward engine nacelles led to a decrease - hence the decision to feed in nose down trim via MCAS as a quick and dirty solution to the certification problem. 

 

 

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It's not fully clear so far how the pilot operated trim interacts with this MCAS trim; we keep getting little  bits of new information (like the fact that the flaps disable the MCAS, and the suggestion that MCAS also affects engine settings).

 

We are told pilot trim temporarily halts the MCAS activity. We are not told if, during this MCAS halt, the pilot is able to trim back up, though given what we now know, I would guess not.

 

And we are not told if the pilot holding the trim switch constantly activated results in a continuous override of the MCAS, though again this seems unlikely, given events.

 

I would guess that MCAS is paused by the activation of the pilot trim switch, but that no up trim results.

 

And I would guess that when MCAS then resumes , a fresh activation of the pilot trim switch is required to pause it.

 

As I understand it. MCAS drives the jackscrew “trim” which moves the entire horizontal stabiliser 2.5 degrees downwards at its extreme, pitching the angle of incidence nose down, possibly beyond the range of the elevators to counteract that nose-down attitude (at that extreme).

 

Happy to be corrected on that detail by someone more knowledgeable...

 

 

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FBI joining criminal investigation into certification of Boeing 737 MAX

 

 

 

 

https://www.seattletimes.com/business/boeing-aerospace/fbi-joining-criminal-investigation-into-certification-of-boeing-737-max/

 

I think it is telling that Europe and Canada will now refuse safety investigations from US authorities (according to ABC Australia).

 

Might that be saying that FAA and Boeing are too closely allied, to the detriment of safety, and the Europeans and Canadians don’t trust them anymore?

 

https://www.abc.net.au/news/2019-03-22/boeing-plans-to-reverse-optional-safety-feature-on-737-max-fleet/10928066

 

 

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