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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

#91

Post by cameldrv »

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?

To elaborate on seiferteric: If the engine were just an unducted fan, the input and output volumes and velocities would be the same, and if they're pointed in opposite directions, there would be zero net force.

In a jet engine though, you have a nozzle on the back, so the input area is greater than the output area. Heating the air also causes it to take up much more volume. These put together, mean that the output velocity is much greater than the input velocity, so there is a momentum transfer from the atmosphere to the plane.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#92

Post by Retra »

anonu wrote: post #48
laretluval wrote: post #2

I hope people are beginning to understand that the presence of software in any system is a liability.

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…

The trend has always been in the other direction. It's easy to reason from first principles when the principles are simple. As more people become experts on our problems, the correct solutions become much more diverse and specialized, and it becomes harder and harder to build integrated systems from first principles.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#93

Post by rpeden »

usefulcat wrote: post #81
jagger27 wrote: post #73

Earlier quoted context omitted.

> 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?

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.

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

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#95

Post by jagger27 »

usefulcat wrote: post #81
jagger27 wrote: post #73

Earlier quoted context omitted.

> 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?

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.

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

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#96

Post by Someone1234 »

danielvf wrote: post #85
Someone1234 wrote: post #51

Earlier quoted context omitted.

> 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…

https://www.google.com/amp/s/amp.theguardian.com/world/2018/... “Indonesian investigators have said the Lion Air Boeing 737 jet that plunged into the sea, killing 189 people in October, was not airworthy on a flight the day before it crashed. They further found that Lion Air must improve its safety culture and better document repair work on its planes. The flight from Bali to Jakarta on 28 October had experienced sim…

> “Indonesian investigators have said the Lion Air Boeing 737 jet that plunged into the sea, killing 189 people in October, was not airworthy on a flight the day before it crashed.

And was repaired between the two flights as I quoted above. Are you selectively ignoring the information in the very post you replied to?

Here's that information again to refresh your memory:

> 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

You and the other poster seem to be basing your whole position on time not moving forward in a linear fashion: Failure, repair, flight. In that order.

Pointing out the previous day over and over while ignoring what occurred in the interim isn't a real argument.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#97

Post by detaro »

laken wrote: post #87
Someone1234 wrote: post #67

Earlier quoted context omitted.

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…

Quoting from the same comment you just replied to: > "On 28 November, Indonesia investigators said the Lion Air jet was not airworthy on flight before crash." "not airworthy" means that it was unsafe.

on flight before the crash. After which it was repaired, and sent on the fatal flight.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#98

Post by markdown »

Xixi wrote: post #57
deugtniet wrote: post #10

Is there something special about the software in new Boeings? Dual engine failure is nothing to sneeze at, and should never happen. Airbus also had its fair share of software errors in history, but if we count the recent Lion air crash as software related, Boeing has had 2 serious software related incidents in a year and I haven't heard anything serious from airbus. Is it because Airbus started its fly-by-wire develo…

The first Airbus FBW airliner was the A320, introduced in 1988 (31 years ago), while on Boeing side it was the 777, introduced in 1995 (24 years ago). By now I don't think it would make much of a difference, if any at all. If anything quarterly reports to shareholders who only care about the very short-term would be the culprit (or management teams whose bonuses only depend on the next quarter revenues). But numbers…

> the more recent the plane the safer it is. As such 787 and A350 are probably the safest airliners currently flying, followed by 777 and A380.

I'd argue that a new model of an old plane like the 737MAX would be safer, Lion Air incident notwithstanding.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#99

Post by Someone1234 »

laken wrote: post #87
Someone1234 wrote: post #67

Earlier quoted context omitted.

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…

Quoting from the same comment you just replied to: > "On 28 November, Indonesia investigators said the Lion Air jet was not airworthy on flight before crash." "not airworthy" means that it was unsafe.

Indeed, in a completely different flight than the one we're discussing.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#100

Post by rpeden »

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?

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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