Discuss: Boeing 737 MAX Grounded

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March 14, 2019 at 05:17:40
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Hi all,

This week's poll question is about news that the Boeing 737 MAX has been grounded in multiple countries following two recent crashes. Discuss here if you think the airplane will quickly be deemed safe again, and, if you like, the poll results themselves.


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March 14, 2019 at 05:58:41
That Boeing was seriously tardy in addressing/recognising the safety issues here is unacceptable. But then Boeing is big player and has "friends" in high places in... One aircraft crashing... start looking seriously as to why; two or more then get "very" serious and ground all those aircraft pending a proper investigation and resolution.

Boeing will do all it can obviously to remedy any apparent/discovered problems; but their focus will be on end of year/bottom line fiscally at the end of the year.

However, at risk of being cynical... Inevitably the potential money lost by a prolonged grounding of these aircraft will influence minds and "encourage" the authorities to relax their position; allowing the aircraft to fly again...

Airlines operate of a risk/ratio basis according to some sources... Which is cheaper long term? Pay more for a safer aircraft and reduce risk of insurance claims post accidents/crashes; or is it cheaper to buy cheaper/less secure etc. aircraft and pay out the insurance as/if the events arrive?

I tend to use SW when flying within US (where viable) and would certainly be inclined to avoid their flights using the current problem aircraft...

Fair to recall that De Havilland was a little tardy when the Comet started to fall out of the sky; due to metal fatigue. At that time Comet was the first commercially employed jet line; and of course there were all manner of problems not then known - not the least metal fatigue.

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March 14, 2019 at 14:25:40
Boeing was late to ground this plane saying "they had found no reason to ground them". I would have thought that two identical planes crashing shortly after take off within months of each other would have been plenty enough reason to ground them.

I got the impression software and procedural fixes were applied to a mechanical problem, which is a bit worrying.

I'm sure they will want to have them flying again ASAP - my guess, within a month. It clearly depends on what they find.

Always pop back and let us know the outcome - thanks

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March 14, 2019 at 23:55:39
From the little I heard, it sounds like the automatic pitch
control system depended on a single sensor to detect a
critical measurement, which I suspect is either airspeed
or pitch. That reliance would be a design flaw.

It sounds like the system pitches the nose down when the
airspeed is so low that the plane is approaching a stall.
Airspeed sensors can get plugged up. I don't know how a
pitch sensor on a plane works. It isn't as simple as using
a carpenter's level while standing still on solid ground.
Such a sensor might be rather complex.

The software fix is said to use multiple sensors, which I
expect are already in place for use by other systems.

I would fly on the plane if I needed to fly. The pilots now
know what to do if the plane suddenly starts to nose down
just after turning on the control. They didn't know before.

-- Jeff, in Minneapolis

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March 15, 2019 at 10:38:49
From what I read similar issues occurred when the pilots engaged the auto-pilot and control was restored after disengaging the auto pilot. I don't think pilots would be engaging the auto-pilot after only 8 minutes. I could well be wrong about that though. Where I was headed here is that there MAY be multiple issues related to this nose down control over compensation. I suspect much of the control of any modern large aircraft includes at least some fly by wire technology. So, the whole problem could be software related. Kind of scary.

I also agree with Jeff in #3 above.

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March 17, 2019 at 02:53:36
In case you did not know, the "so-called" copilot on the Ethiopian 737 MAX 8 had less than 200 flight hours total. This is a ridiculously low amount of flight hours. In the USA the minimum to get a 2nd seat in a commuter plane is 1500 hours. The pilot had supposedly 8000 hours, but it's not specified how many in a 737 MAX 8. My guess is that the "primary cause of this loss of the aircraft is pilot error". Yes, Boeing has to go back and make changes to their autopilot, but would any of you fly with someone that was a "student pilot" in a 737 jet? Go to: https://www.businessinsider.com/eth...

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March 17, 2019 at 03:56:34

Interesting observation, and not information I was aware of.

Whilst the co-pilot may have had only 200 hrs air time the evidence is that the pilot was well up on his hours, though as commented, how many on the 737 Max isn’t known?

There was an excellent film/movie made in 50s starring Jack Hawkins as a test pilot. Two models of the aircraft he was flying, one of several built to test/develop for commercial use, had crashed... His was going the same way... when he managed to recover control and save the day - and the company too.

There was also the classic British film “The Sound Barrier” which was along similar lines. Both films highlighted the commercial interests and pressure surrounding aircraft development.

Incidentally the A10 aka the WartHog went a similar route, as did the WW2 P38 Lightining. Both had a near disastrous development history before they were finally fit for the job... I’m not sure how many fatalities there were before these aircraft were deemed ”acceptable” by whomever.

Commercial interests have long dominated and heavily influenced deployment of aircraft; and similarly cars... Remember the Ford (compact in the USA) Maverick, the Corvair (coffin car), the early version of the American Motors Horizon, and even one model (at least) of. BMW a while back.

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March 17, 2019 at 14:33:59
I don't have any new info since my last post, and that is
minimal. But.... My understanding is that the problem
being addressed by a software/firmware fix is not a
problem with the software/firmware. It is the fact that
only one sensor is used in the pitch control system.
I presume that changes to the software/firmware will
connect the pitch control system to additional sensors
that are already built into the planes, and used by other
systems and the pilots.

If the sensor could fail (some sensors are much less
susceptible to failure than others), then not using more
than one sensor in the pitch control system is a design
flaw. But using only one sensor makes the software/
firmware program and electrical connections simpler,
thus less likely to fail. So a tradeoff.

-- Jeff, in Minneapolis

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March 17, 2019 at 14:56:03
If the sensor could fail (some sensors are much less
susceptible to failure than others), then not using more
than one sensor in the pitch control system is a design
flaw. But using only one sensor makes the software/
firmware program and electrical connections simpler,
thus less likely to fail. So a tradeoff.

Risk ratio classic. Cost of one sensor over two... no doubt the prime factor. Having two would require self monitoring/checking software to ensure that if one went rogue, the other would detect and over ride.

Thanks for further updates/info.

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March 20, 2019 at 12:29:07
This lot raises eybrows:

Always pop back and let us know the outcome - thanks

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March 22, 2019 at 12:01:17
Seems Boeing was indeed playing the risk ratio game as were some of the airlines... Certainly the current words coming out from Washington and investigations there suggest that. Also the FAA seems to have been a little too cosy with Boeing... A warning lamp that could/would have given the affected pilots a chance to do what was necessary to avert a heads down crash - is an optional extra; not fitted as standard....! The FAA allowed that to pass!

Looks like the 737Max is now a dead duck; will not fly again without some serious after sales updates; and possibly no more sold as such. But likely will re-appear as another model - with (some at least) serious modifications and inclusions.

Indonesian Airlines has apparently cancelled their order the Max...

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March 22, 2019 at 18:33:13
So here's my perspective as an outsider with a head full of forgotten half-truths and misremembered lies.

Let's talk about Boeing. According to the rumor mill, nepotism and office politics have overruled any sort of engineering or design concern. As a company, Boeing declared themselves the victor after McDonnell Douglas went out of business and they stopped trying. (PC equivalent would be Microsoft and IE. After Netscape went OoB, all development stopped.) If this sounds like a bad culture for retaining and developing experience in a highly specialized engineering field, well, you won't hear any disagreements from me. This might explain why all new planes coming out are rehashes of previous ones (we're talking about 737 MAX 8 here, as in the eighth version of the 737), and why a single faulty sensor can take out a vehicle with both an autopilot and a backseat driver autopilot.

Let's talk about the FAA. It has succumbed to the same fate as every other government department that has to watch very few very large companies. Namely, they're in bed together. Which is why the FAA rubber stamped the MAX 8, and why no changes to pilot training was required. Nothing new or news worthy, it's just fun to watch the FAA and Boeing finger point at each other now that the heat is on and lawsuits are being drafted.

Let's talk about commercial flight. For a long, long time, the industry has been racing to the bottom. (You can insert your own 737 MAX joke here.) Their goal is to get as many people as possible from A to B as cheaply as possible. This used to be focused on making larger and larger planes, but after the September 11 hijackings, the resulting security theater, and general world economy, there are more and more empty seats in those 787s. Enter the 737 MAX line. Smaller planes means fewer seats to fill, emphasis on efficiency means less fuel costs compared to older 737s.

Let's talk about the 737 MAX 8's engines. They're larger and more efficient; they're also used on Airbus' A320neo line. They're actually too big for the 737. To fit them, the engines are pushed forward and upwards. This throws the MAX 8's thrust off axis, with a tendency to tilt the nose up. Normally not a concern, except when the thrust is at max and the nose is pointed too high. Past a certain tipping point, the (auto)pilots won't be able to tip the nose back to level. The nose will continue to climb, the airspeed will continue to decrease, and the engines ultimately stall. Then the plane enthusiastically revisits the ground tail first. I'm not sure if larger control surfaces with a wider range of motion would resolve the situation, but that'd require more hydraulics, and hydraulics are heavy. Boeing's solution was to prevent the situation with the MCAS.

Let's talk about max thrust. The setting's called Take-Off / Go Around (TO/GA). Guess which parts of the flight see this setting.

Let's talk about the MCAS. It has access to dual angle of attack sensors. If either AoA sensor indicates the nose is too high, it sets the trim to be more nose down and waits for a few seconds. Repeat until the sensor reports things are back into spec, or crash. Key point here is either sensor, not both. There isn't any indication the system was engaging, except for the excessive trim control movement. There is no way to diagnose a AoA sensor mismatch from the cockpit. (It was an optional feature not included here. Literally nickeled and dimed to death.)

Let's talk about trim. Trim's there to keep the plane level if the control stick or yoke is neutral. For reference, these control surfaces are usually on the tail of the plane.

Let's talk about angle of attack sensors. They're basically just horizontally mounted wind vanes. They stick out of the side of the plane, rotate freely along their axis, and the wind rotates it to the angle of least resistance. Now you know your pitch relative to the wind. If you hear anything about something being jammed in relation to a 737 MAX crash or near miss, this is probably what they're talking about.

Let's talk about the response to the first crash. After speculation that it was caused by the MCAS, someone issued an advisory. If you find yourself in the same situation, you should 1) Kill MCAS 2) Disengage the autopilot 3) Fix the trim. That information was being disseminated in the industry, hence the near misses, but not fast enough.

Let's talk about the software fix. Fairly straight forward, I'd imagine. Trigger MCAS only if both sensors agree. Also, Boeing is making the MCAS sensor mismatch alert mandatory, which is nice.

Let's talk about cynical takes. Some, the American press specifically, claim grounding the Boeing 737 MAX 8 is foreign powers striking out against America. Manufactured patriotic hysteria aside, I do suspect China ground the plane as part of their tariff negotiations, and America didn't want to because politics. As for the other countries that followed suit, I don't know if they're trying to give Airbus some edge, if it's some sort of, "me too!" mentality, if they're legitimately concerned about the passengers and crew of these planes, or if it's some anti-America sentiment as the US press claims. Ethiopia's reluctance to send the black box to America suggests at least a little sentimentality is involved.

Let's talk about reading the manual. That's standard operating procedure whenever anything goes wrong in the plane. There's a handful of steps you memorize for a handful of situations, but those situations are times where you will die before you regain control of the plane. Things like initial steps during a sudden cabin decompression. Even then you'll pull out the Quick Reference Handbook (QRH) and look for your specific situation. The QRH lists the steps to perform in a checklist format. Because you're in a stressful life or death situation, and you might miss something important. The big problem in this case is either the pilots misidentified the issue, or the issue wasn't listed in the QRH.

Let's talk about what happened. We won't actually know what went down (the plane) until we get a translated transcript of the cockpit voice recorder. We won't actually know what the plane was seeing until we analyze the flight data recorder. Important steps which were being stalled by Ethiopia.

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