Lion Air: How could a brand new plane crash?

[123apple]

it would seem that the only way to disconnect that thing is to press a switch on the panel or use the trim rockers on the yoke

if they did not find the problem in time they could be in a situation where they have maximum trim down

it sounds like they were fighting the controls for a while (did not realize before trim ended up full down) and just like fly dubai they could not pull up

[HJ1an]

The open question with Lion Air 610 seems to be though, why, if the computer was confused, the crew was unable to go manual and fly the plane back. They were not far from the airport, visibility was good, weather was good, so why not?

From what I've been reading though, there was a switch to turn it off / override it. But apparently Boeing did not cover this in their manual.

[HJ1an]

it would seem that the only way to disconnect that thing is to press a switch on the panel or use the trim rockers on the yoke

Yes, and what is being said is that that is the very thing that Boeing did not include in their training or manual, assuming what I read is accurate.

[123apple]

I thought it was, did they not release a service bulletin reminding them of an already established procedure?

[123apple]

No, it was a system not covered in the FCOM. STS, an existing system of the 737NG was, but MCAS was not. A criminal omission imo.


This highlights that the 737 airframe is not designed for these computerised systems. The Airbus has triple probes - three times less chance of failure. The Boeing only has two. Furthermore, on the Airbus, the protections disengage when a fault occurs, while in this case they merely fly you into the ground... that being said, the Airbus has had issues with dual probe failures (ref QF73, XL88T), but apart from that the airbus is much safer with a higher degree of redundancy, as well as being designed from the beginning to work with these systems.

[HJ1an]

[IAHM-COL]

https://www.latimes.com/business/la-fi- ... story.html


This article could've been written by KL-666~!

[123apple]

though not all, aircraft have three sensors for critical readings, allowing a computerized voting system to eliminate a discrepant sensor.

That is the basic flaw in Boeing's design. The 737 is not designed for computerised systems, being a much older design. In the 1960s a faulty sensor wouldn't cause a crash. On the other hand if you have three sensors, you won't have any problems (until two fail, of course -- but how rare is that?) with faulty sensors as the faulty data is rejected. This makes any Airbus much safer than any Boeing aircraft with the MCAS feature -- I will certainly not fly on any Boeing 737 MAX in the Western world much less in Indonesia or anywhere else.

[HJ1an]

I always wondered why the plane did not allow the pilot to have ultimate control as did the 787. This surely looks like Boeing is responsible (or at least, that one /two guy / team doing the flight computer systems / writing the manuals and instructions).

However, there is a theory going that the sequence of about 7 missteps leading to disaster. If just one is corrected or a mistake caught in time, a complete disaster is easily avoided. In this case there is many;

1. Boeing implementing flawed/ missing out the vital pilot information
2. The pilots from previous flights did not turn back (unsure if this would actually complete stop or would just delay its inevitably though)
3. Engineers did not ground the plane or do a flight check
3a. Engineers or pilots keeping quiet for they did not want to be the ones responsible for delaying company costly operations
4. Disaster pilot(s) did not, or not knowing to flip the elevator switch off
4a. Previous pilots conveying problem *and solution* for when encountering it.

Aside from 2, which is rightfully questionable, if they had done any of this in the point in time the disaster would not have happened. Sure, this is hindsight talking about 20/20, but then this is always my concern - new planes do not necessarily mean safer, it just means new unknowns. I put the same set of concerns to autonomous driving cars, btw.

[HJ1an]

One of the controls—the electric stabilizer trim thumbswitch on the pilot’s control yoke—could temporarily reset MCAS’s control over stabilizers. The Lion Air pilots hit this switch over 24 times, buying them some time—but MCAS’ stall prevention software kicked in afterwards each time because of faulty data coming from the aircraft’s primary angle of attack sensor.

Completely disabling MCAS’ control over the aircraft’s stabilizers would be the only way to overcome that sensor failure in the current software version. That requires throwing two additional switches on the console and turning a trim wheel on the console manually to re-establish manual control.

https://arstechnica.com/information-tec ... -disaster/