[lukehutch]

Planes can be switched out last-minute. I plan to check the plane type at the gate every time I fly for the next 10 years, and if it's a MAX, I'll reschedule my flight on the spot.

They claim they solved the software problem, but they didn't solve the physics problems created by the engine position (which necessitated the software in the first place).

[pdonis]

> they didn't solve the physics problems created by the engine position

The engine position, in itself, isn't terribly unusual; the 757 and 767 both have engines in similar forward positions on the wings and have a similar pitch up moment due to the engines at high angles of attack. So do a number of Airbus models. Designing flight controls to deal with this issue is not new and has been well tested.

The particular issue with the 737 MAX was that Boeing wanted to change the engine position on an existing aircraft, without requiring a new type certification and pilot retraining. That meant that the flight controls had to not just properly account for the engine position, but to do so while keeping the same stick force curve vs. angle of attack as existing 737 models. That is what drove the MCAS software system that caused all the trouble. If the plane had been designed as a new type from the start, the engine position would not have been an issue; and the redesign is basically doing what a new type design would have done, as far as I can tell from the documents the FAA has published.

[bostonvaulter2]

Does the 737 MAX now require pilot retraining? Or did they make some other sort of adjustment?

[hehetrthrthrjn]

Yes it's required.

[bostonvaulter2]

I'm very glad to hear that!

[quotha]

> If the plane had been designed as a new type from the start, the engine position would not have been an issue

Because the engineers would not have positioned the engines there in the first place.

[pdonis]

> Because the engineers would not have positioned the engines there in the first place.

That would have been one possible approach, yes, but it would have involved other changes, the main one being longer landing gear and a higher ground clearance.

My point is that even having the engines in a similar position to the existing one would not have posed a problem if the plane had been a new type. Other planes in service have engines in a similar position. What caused the problem was having the engines in that position and having to match the stick force curve of the existing 737 in order to keep the same type rating.

[drawkbox]

On top of that there was a single angle of attack (AoA) sensor active that was complained about and failed hundreds of times. [1]

Not only is that a single point of failure, it is more easily sabotaged or easily damaged.

Besides the fact the plane has engines too big for it and needed this MCAS system simply to retrofit and route around regulations and deal with that by constantly checking the AoA to trigger nose down adjustments, this is bad engineering/product design by management.

The software now takes two sensors into account in case of a failure of one but is still a problem potentially. Not sure if software can solve this.

[1] https://www.cnn.com/2019/04/30/politics/boeing-sensor-737-ma...

[J-dawg]

In the original design, wasn't there an optional safety feature that added a second AoA sensor? It seems unbelievable, and is possibly one of the most ridiculous things about this whole story.

Presumably as part of the update, this optional feature has become standard?

I'd also like to see a list of all the airlines that chose not to spec the additional sensor in their initial order of the aircraft. It probably says a lot about their safety culture.

[detaro]

From what I understand, the plane always has two sensors and MCAS always only used one of them (with Boing arguing that the pilot was the "redundancy"). The plane was supposed to show an alert when the two sensors disagreed, but Boing made a mistake and that alert only showed when the airline had purchased an additional add-on package to show the sensor value in the pilot display. Boing discovered this in 2017, but did not consider this a safety-critical defect and thus didn't inform anyone or prioritize a fix, despite internally also assuming that the pilot realizing the issue within seconds was the redundancy for correcting MCAS.

[alavesto]

Boeing's expectations for pilots recovering from an MCAS error were criminal. With an erroneous AOE reading, MCAS would immediately and repeatedly force the nose down. Pilots, not even told that MCAS existed, would somehow need to quickly recognize it as a powered flight control problem, cut off power to the stabilizer, and use the manual trim wheel to raise the nose - which can be physically impossible at high speeds in a nose-down attitude.

No rational person would think this system wouldn't kill people. The people responsible committed manslaughter.

[J-dawg]

Thanks for that explanation. I think this was misreported at the time (or I just wasn't paying attention!).

In a way what you described is worse: a known bug that they decided not to fix.

I'm surprised that displaying the sensor value wouldn't be a standard feature.

[ummonk]

I'm going to try to choose airlines that fly Airbus instead for a few years just to be safe.