Boeing 787 Suffers Rare Dual Engine Failure on Landing

Post by usefulcat » Wed, Jan 30, 2019, 5:30 PM UTC

jagger27 wrote: post #73

ravingraven wrote: post #62

Earlier quoted context omitted.

No, it would not. If the engine is shut down moments before touching down it would mean that there would be no reverse thrust after touching down since it takes a considerable amount of time to re-start a turbo-fan (not 60 seconds as OP wrote as the engine is still spooling but still a significant amount of time and I don't think that any pilot would go through the workload and checklists of re-starting an engine dur…

> 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?

Post by AnimalMuppet » Wed, Jan 30, 2019, 5:30 PM UTC

dmead wrote: post #77

anonu wrote: post #48

Earlier quoted context omitted.

I think software has existed in computer systems for 7 or 8 decades now - and the pitfalls are well understood. I think the problem is one of simplicity vs complexity. New systems today rely on dozens - hundreds even - of packages and libraries - many of which are not written by the implementer. How can you ensure reliability in all these components? This is why engineering from first principles - even in today's sof…

you would be wrong.

Post by danielvf » Wed, Jan 30, 2019, 5:31 PM UTC

Someone1234 wrote: post #51

danielvf wrote: post #30

Earlier quoted context omitted.

That aircraft was being knowingly flown with [edit: a broken sensor]. It was unsafe on takeoff. The final problem that brought the aircraft down - the trim run-away - happens all the time in airliners you've flown in. When the run-away starts, the pilot is supposed to flip two switches to disable the trim system motors. In the Lion Air crash, it is indeed believed that a software bug from the misbehaving sensors star…

> That aircraft was knowingly flown with multiple broken sensors. It was unsafe on takeoff. You'll need to cite that, since it contrary to any information I can find on the Lion Air accident e.g.: > The chief executive officer of Lion Air, Edward Sirait, said the aircraft had a "technical issue" on Sunday night, but this had been addressed in accordance with maintenance manuals issued by the manufacturer. Engineers h…

Post by laken » Wed, Jan 30, 2019, 5:32 PM UTC

Someone1234 wrote: post #67

teraflop wrote: post #56

Earlier quoted context omitted.

From the same Wikipedia article that was just linked: > "The aircraft suffered an airspeed indicator problem for its last four flights, including the flight to Denpasar. Thinking that it would fix the problem, the engineers in Bali then replaced one of the aircraft's AoA sensors, but the problem persisted on the penultimate flight [...] [the crew] recorded a twenty-degree difference between the readings of the left A…

Those are prior flights. The aircraft was fully repaired: > The chief executive officer of Lion Air, Edward Sirait, said the aircraft had a "technical issue" on Sunday night, but this had been addressed in accordance with maintenance manuals issued by the manufacturer. Engineers had declared that the aircraft was ready for takeoff on the morning of the accident So you still haven't supported your extraordinary claim…

Post by alliecat » Wed, Jan 30, 2019, 5:33 PM UTC

seiferteric wrote: post #54

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?

Your forgetting that the cool dense intake air is expanded (greatly) in the engine via combustion with fuel, so the volume of air being exhausted is much greater than went in and at much higher pressure, this is where the thrust comes from in the first place. It's not just a big fan :)