Hacker News new | past | comments | ask | show | jobs | submit login

Again, every pilot knows about Dutch Roll; it may have caused problems before, but everyone knows about it, and as far as I'm aware, no one ever hid it's existence from pilot's for the sake of certification and sales.

No one was told about MCAS or the force inversions it was meant to correct ahead of time, or shared enough technical detail to ensure pilots know what to be prepared for. Major difference there.

>On the other hand, dealing with runaway MCAS is literally just turning a switch off on the console.

Which instantly decertifies your aircraft to be carrying passengers.

Look, I get it. That's paperwork talk! The thing still flies!

But we have to hold ourselves accountable to the silly whims of paperwork talk, lest we fall victim to Normalization of Deviance, who is a cold-hearted, stone-faced bitch.

> Again, every pilot knows about Dutch Roll;

Knowing about it doesn't help. They crash anyway. That's why there's a yaw damper as required equipment.

> No one was told about MCAS

That's true, but they were told about the stab trim cutoff switches to halt runaway trim, and the MCAS failure exhibits itself as runaway trim. The flight before the Lion Air crash had an MCAS failure, too, and the pilots simply switched off the stab trim and they landed safely. They did't know about MCAS, either.

> Which instantly decertifies your aircraft to be carrying passengers.

That isn't how certification works.

Boeing has certainly made many mistakes with the MCAS system, but the problem was controllable by pilots who remembered what the cutoff switches were for. This was proven in the first MCAS failure incident I mentioned.

>Knowing about it doesn't help. They crash anyway. That's why there's a yaw damper as required equipment.

They don't do it not knowing about and having experienced Dutch Roll, however, with a check pilot. We train for the unexpected, use technology as best we can to mitigate, and just have to have faith that after a certain point we've told the pilot everything they need to know, and leave them to do their thing. Regardless of whether Dutch roll has killed someone or not they knew about Dutch roll going into it. They knew yaw dampers were a thing. They knew how and when yaw dampers were active and why. Not so with MCAS.

>The flight before the Lion Air crash had an MCAS failure, too, and the pilots simply switched off the stab trim and they landed safely. They did't know about MCAS, either.

Walter, c'mon man. We've been through this before.

The penultimate Lion Air flight had 3 pilots, one with the luxury of paying attention to anything the other two actually flying the plane weren't; None of them knew what was going on, and to be frank, Getting it right for the wrong reasons just sets the stage for more disaster later. You can also look at the documentation regarding stabilizer runaway, and it is specifically described as a continuous uncommanded trim actuation.

MCAS isn't continuous, it's discrete. On for 10 seconds, off for five. While the procedures may be the same, an unprimed pilot being caught unawares by an aircraft feature completely foreign to them, and unelucidated in the documentation is liable to lose precious time if the failure happens at an inopportune time of the flight.

Also, throw in the failure of autopilot to stay engaged, and inability to lock the computer out without losing the trim switches, it's a losing proposition all around.

>That isn't how certification works.

I'll butt heads with you there. A type certification certifies a particular configuration of hardware and software to be flown in certain airspace for a particular purpose. While operational leniency is to be expected so a failure of a component not on the Minimum Required Equipment checklist doesn't ground planes at every little problem, I patently reject the proposition that having a type certificate granted, then experiencing a configuration change during normal operation that compromises the ability for the airframe to meet the prescribed criteria for being certified as airworthy does not discertify that particular instance of the alleged type from immediate airworthyness.

It is the configuration that is certified. Anything that meets that configuration within reason may be used for the certified purpose. Departure from said configuration warrants immediate remediation as quickly and safely possible. Generally that judgement call is by custom left to the pilots as to whether to continue or reroute for repairs.

If you lose a system required to use the plane for it's intended purpose in flight, then you should damn well be prepared to put that plane on the ground to get it fixed. Period. This type of thing isn't a game, and the more the industry treats it like one, the less inclined people will be to trust and utilize it.

> it's a losing proposition all around.

Obviously it's not as the pilots in the first incident turned off the stab trim and landed without further incident or difficulty, despite being totally unaware of MCAS.

10 seconds of the stab trim moving is a long time, and it's hair-splitting to say that isn't a runaway when it is uncommanded and moving things in an obviously dangerous direction. Short circuits can also cause runaway trim, and are often intermittent.

They do not have to know what is going on to conclude it's runaway trim and shut it off. The pilots are supposed to be trained for runaway stab trim. It's the WHOLE POINT of having the cutoff switches within easy reach on the console.

Just like if the engine is on fire, the pilot does not need to know why the engine is on fire, he just has to know how to operate the engine fire extinguishers.

Furthermore, the MCAS system was known after the first crash. Boeing issued an airworthiness directive about it, with instructions to use the cutoff switches.

So what is the reason the Ethiopian pilots were not aware of the MCAS system (it was all over the news, and Boeing had issued an airworthiness directive on it which is supposed to be sent to the pilots)? I don't know. I've never heard an explanation for it.

Nobody is claiming it's a game. Nobody is claiming Boeing doesn't need to fix the MCAS system. Pilot training is clearly inadequate if two sets of pilots did not use the cutoff switches. Something is wrong with the airworthiness directive system if they did not reach the pilots.

Applications are open for YC Winter 2020

Guidelines | FAQ | Support | API | Security | Lists | Bookmarklet | Legal | Apply to YC | Contact