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A comment on Boeing 787 Suffers Rare Dual Engine Failure on Landing. Parent comment

Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by jagger27 on Wednesday January 30, 2019 @12:25PM (#19037105)
> or to only engage reverse thrust once the landing gear has weight on it.

Having reverse thrust depend on a sensor that could fail seems like a poor choice. What if the landing gear don't drop? Is there a situation where you would still want reverse thrust without landing gear?

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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by rpeden on Wednesday January 30, 2019 @12:39PM (#19037265)
Sometimes you'd like to have reverse thrust in-flight if you want to descend really, really quickly. Airliners don't have that feature anymore, but the C-17 and C-5 do.

Actually, maybe some ex-Soviet airliners can still do it. DC-8s being used by cargo airlines could possibly still technically do it, but don't use the ability.

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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by mrguyorama on Wednesday January 30, 2019 @12:58PM (#19037456)
Specifically, it wasn't a design goal of reverse thrust, and it's operation mid-flight was directly responsible for over 200 innocent lives lost[0]. Thrust reversers are very much a "nice to have" feature on turbofan aircraft, with every one qualified to both land and initiate a rejected takeoff at maximum weight without using them, though not without some maintenance after.

[0]: https://en.wikipedia.org/wiki/Lauda_Air_Flight_004

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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by ravingraven on Wednesday January 30, 2019 @12:49PM (#19037350)
Most things in aircraft automation systems depend on sensors that could fail (those sensors could be redundant etc. but the same can be done with the sensors on landing gears). It is sane design.

> What if the landing gear don't drop?

I don't think that there is need for reverse thrust in such a scenario.

> Is there a situation where you would still want reverse thrust without landing gear?

Even if there is, there could be a manual override.

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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by Wintereise on Saturday February 02, 2019 @01:44AM (#19061556)
> I don't think that there is need for reverse thrust in such a scenario.

How do we slow down planes that still need to come down despite a stuck landing gear, then?

Indeed, a manual override must exist.

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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by usefulcat on Wednesday January 30, 2019 @12:30PM (#19037154)
How would that work exactly? Surely the engines will be among the first things to be destroyed on 'landing' if the gear aren't down.
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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by rpeden on Wednesday January 30, 2019 @12:35PM (#19037222)
It depends on where the engines are mounted. There was a Tu-154 that landed gear-up in Greece, then took off again, dropped the landing gear, and landed normally.

https://en.wikipedia.org/wiki/Mal%C3%A9v_Flight_262

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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by jagger27 on Wednesday January 30, 2019 @12:36PM (#19037234)
There are plenty of examples of non-catastrophic belly landings. I'm no pilot or aircraft engineer, so I don't know for sure if you'd want reverse thrust in such a situation. https://en.wikipedia.org/wiki/Belly_landing
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Re:Boeing 787 Suffers Rare Dual Engine Failure on Landing by threeseed on Wednesday January 30, 2019 @02:11PM (#19038207)
Just have multiple sensors like they do already.

It's also a sensor that you can simply put on each wheel to determine if there is weight applied.

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