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Boeing 787 Suffers Rare Dual Engine Failure on Landing

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Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#151

Post by vpribish »

alliecat wrote: post #88
exabrial wrote: post #12

Sort of off topic, but reverse thrust sort of boggles my mind. If you're sucking air in from the front of the aircraft and ejecting it out the front, don't those forces counterbalance each other?

"Sucking" doesn't actually generate any thrust - In highschool, my physics teacher did a demo with a T-shaped pipe with a fan in the middle, suspended from some string. Without the T, the pipe moved as you'd expect. With the T directing the airflow in equal proportions perpendicular to the axis of the pipe, the pipe stayed still as if the fan wasn't on at all.

physics says no. There was something wrong with that demo if this was the conclusion.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#152

Post by maxxxxx »

ergothus wrote: post #116
maxxxxx wrote: post #112

Earlier quoted context omitted.

I always love it when you have worked on something for months and someone new comes by and says "Why don't you just X?".

It's worse when they are right though. I wish I could say that had not happened to me.

I am fine with that. In most cases they aren't though. Or they don't understand the whole environment.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#153

Post by Rooster61 »

JBReefer wrote: post #149
Rooster61 wrote: post #145

Earlier quoted context omitted.

Oddly enough, your comment makes me think that you are writing it from the perspective of a member of the very group of programmers you decry. Companies that write high-risk, life-critical systems don't just let any ole J. Random Hacker work on such critical systems, and I don't think anyone who has worked in such a field would realistically think that these "brogrammers" as you say would be seriously considered for…

Aren't almost all of the software engineers on those projects writing tests and formally verifying software?

Sure, but tests are only as good as the programmers that write them (and that's if those programmers are GOOD at writing tests, which is not universal). Not to mention no amount of automated testing is foolproof.

Full disclosure, I design and write system software tests for a living.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#154

Post by the_mitsuhiko »

cm2187 wrote: post #50
code4tee wrote: post #19

Boeing’s answer seems to say if you accidentally pull the thrust reverser lever before the aircraft is on the ground it just force shuts down the engines. That sounds like an odd safety override. Surely a better solution would be to just not activate reverse thrust. Unlike car engines a jet engine can’t just be quickly restarted if it accidentally shuts down. It typically takes 30-60 seconds to get going. This and ea…

I thought that most modern aircrafts were not allowing the reverse to be deployed if the wheels didn't touch the runway. Talking about an odd safety override. It's kind of a self-destruct button.

Lauda Air flight 004 crashed because of that.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#155

Post by asdfadsfgfdda »

exabrial wrote: post #12

Sort of off topic, but reverse thrust sort of boggles my mind. If you're sucking air in from the front of the aircraft and ejecting it out the front, don't those forces counterbalance each other?

Think of the net momentum balance. Some mass of air is entering the intake at low speed, the engine does work on the air, then the air exits the front at very high speed. The intake speed is approximately the airplane's speed (150 mph), while the exhaust speed is probably 500 mph.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#156

Post by t0mas88 »

sargun wrote: post #40

How do you restart the Boeing 787 in mid-air? With the lack of an APU (they use li-on batteries, I think?), what's the mid-air engine restart procedure?

Just like any other jet enige... Get it to spin fast enough, enable the igniters and add fuel. Be careful with how fast they spin before adding fuel, too slow and things get very hot and melt.

Getting them to spin fast enough in a 787 is a bit different from a traditional jet engine, because traditionally you spin them by pneumatic power (from ground, APU or the engine) and in the 787 you spin them by electric power (from ground, battery, APU, other engine or RAT). But there isn't much difference from a pilot's point of view.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#157

Post by hodgesrm »

sschueller wrote: post #6

"Boeing said that selecting full reverse too quickly upon landing before the aircraft has fully transitioned to ground mode could cause the system to activate." That sounds like apple's "you are holding it wrong" when "antenagate" happened. Not something I want to hear from an aircraft company where people's lives depend on it working.

Aircraft are very different from cell phones. There are a number of things you can do as a pilot that will cause them to crash or stall especially if something unusual like a sensor or engine failure occurs. Pilots spend a lot of time in simulators practicing how to fly the plane in a variety of such situations as well as under normal operating conditions.

Or as my neighbor says: "I've dealt with hundreds of engine fires!" (He flies A320s.)

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#158

Post by Retric »

ergothus wrote: post #116
maxxxxx wrote: post #112

Earlier quoted context omitted.

I always love it when you have worked on something for months and someone new comes by and says "Why don't you just X?".

It's worse when they are right though. I wish I could say that had not happened to me.

Is that from other experts with a very close understanding of the specifics, or random people online?

What I find is you start with several viable approaches, pick one and go down the path enough to figure out the downsides. At which point you need to decide to backtrack or keep going. That’s the hard part not simply coming up with a seemingly simple solution.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#159

Post by 98codes »

nck4222 wrote: post #110
code4tee wrote: post #19

Boeing’s answer seems to say if you accidentally pull the thrust reverser lever before the aircraft is on the ground it just force shuts down the engines. That sounds like an odd safety override. Surely a better solution would be to just not activate reverse thrust. Unlike car engines a jet engine can’t just be quickly restarted if it accidentally shuts down. It typically takes 30-60 seconds to get going. This and ea…

Do you have experience with aircraft engine design, or landing protocols, or insight in to the meetings when the engines were designed? If so, I'll take back my words but considering the manufacturer doesn't know exactly why this happened, and the engineers on the ground said it seems like a "software bug", it seems a bit presumptuous and frankly a bit comical to start saying things like: "Surely a better solution wo…

Welcome to the internet, where everyone's an expert, the problems are real, and the points don't matter.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#160

Post by vpribish »

minedwiz wrote: post #17
exabrial wrote: post #12

Sort of off topic, but reverse thrust sort of boggles my mind. If you're sucking air in from the front of the aircraft and ejecting it out the front, don't those forces counterbalance each other?

Reverse thrust doesn't come directly out the front of the engine - it's vented out the side (or, in very old engines, redirected from the back exhaust): https://upload.wikimedia.org/wikipedia/commons/d/df/F-GTAR_A...

that is a misleading way to put it - the reverse-thrust air does indeed move toward the front of the plane. it also moves outward, and is often taken from the sides of the engine, but a component of the (reversed) thrust is definitely going opposite the usual direction.

here is a thermal image of a modern jet with thrust reverses on : http://www.rusaviainsider.com/russias-mc-21-tested-for-rever...

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