Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Boeing 787 Suffers Rare Dual Engine Failure on Landing

thepointsguy.com

Post reply on HN
Print view View original

291–300 of 365 posts

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#291

Post by ChuckMcM »

salawat wrote: post #184
ChuckMcM wrote: post #132

Earlier quoted context omitted.

Reminds me of the quote, "For every complex problem there is an answer that is clear, simple, and wrong." -- H.L. Mencken One of the things I have experienced in my career is the mind boggling complexity of the software in systems that are capable of killing people. The more people it can kill the more complex the software. As a result when I read articles like the one posted I find it tantalizing to speculate about…

If the reverser could rip the engine off the wing, it wouldn't be safe to engage on the ground. Just thought that was worth pointing out. A reverser only redirects thrust, and only generates about 60% of max thrust pushing backwards. It's only on for a limited time on the ground because under a certain speed, you run the risk of blowing FOD into the intake path, putting the engine at risk. I'm not aware of any reason…

Apropos, the Wikipedia article (https://en.wikipedia.org/wiki/Thrust_reversal) mentions number of events where an engine reverser was deployed in flight, one involving a 767 which resulted in the loss of the aircraft.

That counts as a pretty serious thing to avoid :-).

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#293

Post by madeofpalk »

cm2187 wrote: post #114
metalliqaz wrote: post #70

Earlier quoted context omitted.

It's not an odd safety override. An overthrust situation is always dangerous for various reasons. One of the more spectacular is the possibility of liberating airfoils from the engine and shooting them into the cabin. It's not a self-destruct button, it's anti-destruct limit. As for the thrust reverser, there are many integrated systems on the aircraft. It's possible that the cockpit detected weight-on-wheels, but th…

By self destruct, I meant switching off the engines in flight seems to me to be a terribly dangerous behavior.

You would be surprised at just how safe and 'normal' shutting off the engines on a plane is.

Related, British Airways Flight 268, a B-747, when taking off from LAX had a problem with one of it's engines so they shut it off, and continued flying all the way to London, albeit to Manchester instead of Heathrow, with one less engine. https://en.wikipedia.org/wiki/British_Airways_Flight_268

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#294

Post by dorfsmay »

esemor wrote: post #189

I think the auto shutdown of engines in flight, in case it senses reverse thrust, is a great design. The 787 is a replacement for my 767 (currently a pilot on the aircraft) and in 1991 a Lauda Air 767 suffered a failure in one of its thrust reverser and it became activated during cruise. The aircraft was destroyed in flight. The thrust reversers should not activate during flight (a air/ground sensors prevents that) b…

As long at it is well documented and part of the training, and also ideally the system should indicate to the pilot why it is shutting down the engine(s), to avoid something like this:

https://en.wikipedia.org/wiki/TAM_Transportes_A%C3%A9reos_Re...

"The safety system automatically cut the power to the engine suffering the thrust reverser malfunction. There was no alarm in the cockpit to indicate that a thrust reverser had been accidentally deployed. The crew had no way of knowing what the true problem was. The copilot, seeing the right engine power lever automatically move to the closed position, thought that the lever had slipped back and pushed it back to the full power position alongside the left engine throttle lever. Once again, the automatic safety system closed the right engine throttle and the captain, who was conducting the takeoff, called for the autothrottle system to be switched off. After switching off the system, the copilot again pushed the right engine power lever fully forward and forcefully held it there."

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#295

Post by camtarn »

stevehawk wrote: post #278
isostatic wrote: post #234

Earlier quoted context omitted.

You never missed a gear, thinking you were driving a 6 speed rather than a 5 speed?

No, but for as long as I've been driving manual cars they've had gates to prevent that very action. (1995)

Not mine (Honda Jazz). But you physically can't do it, as the reverse gear has no synchro and won't mesh unless stationary.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#296

Post by jzwinck »

cbhl wrote: post #139

The Boeing 787 is now about nine years old. I wonder how much of this is operator proficiency triggering latent bugs (aka, "pilots got too good at pushing buttons quickly"). The bugs in the Therac 25 were only discovered after the machine had been in production for a while (you had to be typing "too quickly" in order to get the software to trigger the bug with the safety interlock).

The Ryanair booking website has several bugs exactly like what you describe. If you use it too quickly it won't sell you plane tickets. If you use it more slowly it works fine.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#297

Post by a1369209993 »

gugagore wrote: post #241
a1369209993 wrote: post #231

Earlier quoted context omitted.

> I was hoping "roughly speaking an order of magnitude" would go down to 3. I'd call that half a order of magnitude, considering log₁₀(3) is around 0.477. So you're off by more than a factor of two.

You know, I considered saying that the "roughly" buys me a factor of two in log space. I didn't want to be that person, but I'm glad you were ;).

It's surprisingly non-trivial to pin down exactly what the 'correct' scale[0] for a given measurement is. I do agree about "roughly" generally being up to a factor of two in the appropriate scale[1], although I'm the sort who thinks a 19% increase (or 16% decrease) should be called a quarter of a factor of two.

0: Uniform, linear and logarithmic are obvious candidates, but depending on the domain you can end up with some really wierd scales (eg floating-point ULPs, which can look logarithmic or linear, but aren't either).

1: hence > So you're off by more than a factor of two.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#298

Post by heyjudy »

esemor wrote: post #189

I think the auto shutdown of engines in flight, in case it senses reverse thrust, is a great design. The 787 is a replacement for my 767 (currently a pilot on the aircraft) and in 1991 a Lauda Air 767 suffered a failure in one of its thrust reverser and it became activated during cruise. The aircraft was destroyed in flight. The thrust reversers should not activate during flight (a air/ground sensors prevents that) b…

Hmm. There might need for a sooner transition point for that particular inhibition. Perhaps somewhere between ground effect (well below minimums) and back trucks are turning.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#299

Post by dsfyu404ed »

inferiorhuman wrote: post #276
dsfyu404ed wrote: post #206

Earlier quoted context omitted.

Even a 1950s era transmission will still be very hard to force into a gear if the speed difference is too great. Likewise you'll have a very difficult time shifting into reverse or 1st at speed. That's just how syncros work. You might be able to overcome it by double clutching but it would require conscious effort. Even just shifting to reverse while rolling is difficult.

Still possible though. Years ago a friend and I pulled a manual transmission in a junk yard. He got it home, installed it, and then discovered reverse was completely stripped.

A stripped reverse gear would be indicative of failure to put it in reverse.

If the connecting rods had fled the engine that would indicate that someone succeeded in getting it into a gear it didn't want to be in.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#300

Post by noir_lord »

mhh__ wrote: post #271
noir_lord wrote: post #207

Earlier quoted context omitted.

I don't know, I suspect software resiliency is one of those "gets exponentially more expensive as you approach perfect" situations and a robot could bash inputs at speeds a human couldn't in thousands of orders, it would certainly let you test those weird code paths that blow up when they are never exercised until they are.

It does get exponentially more expensive, which is why you have to pick a certain level of ~perfection~ and then stop. Also, the robots would have to bash at the speed of a human: The point is to mimick human inputs not necessarily test every code path (Which you could do in software)

When testing resiliency software testing isn't the whole of the thing.

I spent a lot of time at new job (well 18mths now) on making the software side more resilient, we still had a site wide outage of internet access and comms and internal systems because one of the women in the sales office unplugged a socket in the ingress comms cabinet to plug her hair straighteners in.

Coincidentally my request to have physical access control on all the comms cabinets shot right up the list.

The boundary layer between software and hardware itself has to be tested, the real world is a messy place :).

Post reply on HN