Getting a 787 back in the air after a diversion • Hacker News Board

Re: Getting a 787 back in the air after a diversion

#31

Post by sajomojo » Sat, Jan 04, 2020, 6:23 AM UTC

WalterBright wrote: post #24

sajomojo wrote: post #18

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles. If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the oc…

> If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the ocean is entirely driven by a desire to maximize airline profits. That intuitively makes sense, but it's incorrect. The FAA certified twin engines over water because it's safer. Half the number of engines mean half the failures, and ha…

Can you point to the statistics? I'm sure modern twin-engine planes are more reliable than very old four engine planes but what about modern vs modern?

Re: Getting a 787 back in the air after a diversion

#32

Post by DuskStar » Sat, Jan 04, 2020, 6:28 AM UTC

sajomojo wrote: post #18

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles. If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the oc…

The only thing that a 3rd+ engine helps with in this context is uncorrelated engine failures. (Correlated ones - like "oops we used the wrong fuel units" or "that volcanic ash cloud sure is pretty" - are the same for two engines as they are for 4)

These failures are really, really rare. A very conservative approximation would be one in 100,000 flights. (That would be once every other day in the US, for reference. Like I said, conservative) That means you'll have both engines fail randomly every 100,000,000,000 flights, which frankly no one cares about.

Carrying around an extra engine for the 1 in 100+ Billion situation it'll be useful isn't a good idea. It'll probably kill more people than it saves, for that matter - how many extra compressor disks will be thrown into cabins because of that?

Re: Getting a 787 back in the air after a diversion

#33

Post by greglindahl » Sat, Jan 04, 2020, 6:29 AM UTC

jandrese wrote: post #9

dehrmann wrote: post #5

Earlier quoted context omitted.

I might get some of the backstory halfway off, but my grandfather was in Alaska during WWII for the construction of the Alaska Highway. They tried to never turn off truck and equipment engines because if you did, you had to build a fire under them to get them warm enough to start again.

Old farm tractors used what was called "farm oil" in the old days. Basically the cheapest form of fuel you could buy since it was effectively a byproduct of the refining process. It was closer to paraffin wax than diesel, solid at room temperature. In order to start the tractor there was a second tank with diesel that was used until the engine warmed up enough to melt the primary fuel. If your tractor stalled out and…

Is this the same as the "bunker oil" burned by big ships? Wikipedia seems to think so: https://en.wikipedia.org/wiki/Fuel_oil#Bunker_fuel

Re: Getting a 787 back in the air after a diversion

#34

Post by sajomojo » Sat, Jan 04, 2020, 6:30 AM UTC

jacquesm wrote: post #26

sajomojo wrote: post #18

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles. If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the oc…

Contrary to your assertion the two engined craft are just as safe (or safer!) as the four engined craft because of changes in procedures. Fuel management, weather forecasting, general engine reliability, lubricant reserves are all different and much more stringent for a twin engined jet over water on a straightline route. The effect is the aircraft is less long in the air anyway which has a big effect on the risk cal…

Doesn't the fact that the twin-engine planes have to submit to more stringent ETOPS requirements mean the FAA believes they're less reliable than four engine planes?

Re: Getting a 787 back in the air after a diversion

#35

Post by inferiorhuman » Sat, Jan 04, 2020, 6:30 AM UTC

fnbr wrote: post #12

acomjean wrote: post #7

Earlier quoted context omitted.

Cars in northern Canada sometime have block heaters installed for cold starting. How cold should it be before you use it? Ask the internet: https://www.theglobeandmail.com/amp/globe-drive/culture/comm...

In my experience, it's all cars in Canada- I've never seen one that doesn't have it (other than imports). I guess you could probably get away without it on the west coast. Most cars do start though. It’s really a maintenance issue, where it’s bad for your car to start it at -30 (as the linked article says). In my experience, a newer car in decent shape will start consistently.

Yeah my E39 doesn't have any sort of heater and it came from BC. I've not seen anywhere to plug a block heater in though BMW did sell auxiliary coolant heaters (from Webasto). Of course if I lived in a climate where block heaters were required a BMW wouldn't be my first choice. The heated seats and steering wheel come in handy more than I thought they would tho.

Re: Getting a 787 back in the air after a diversion

#36

Post by sajomojo » Sat, Jan 04, 2020, 6:32 AM UTC

DuskStar wrote: post #32

sajomojo wrote: post #18

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles. If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the oc…

The only thing that a 3rd+ engine helps with in this context is uncorrelated engine failures. (Correlated ones - like "oops we used the wrong fuel units" or "that volcanic ash cloud sure is pretty" - are the same for two engines as they are for 4) These failures are really, really rare. A very conservative approximation would be one in 100,000 flights. (That would be once every other day in the US, for reference. Lik…

Except this ignores that the motivation was not increased safety but money. It does seem true that twin-engine planes can be quite safe but if Boeing/Airbus were motivated to create the safest possible plane, it would probably have four engines.

I doubt the US President will be flying on a twin-engine plane any time soon. They'll choose the safest (American made) option. Probably an updated 747 model, no?

Re: Getting a 787 back in the air after a diversion

#37

Post by inferiorhuman » Sat, Jan 04, 2020, 6:36 AM UTC

sajomojo wrote: post #18

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles. If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the oc…

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles.

You're right, and that's why 787s with Rolls Royce engines had their ETOPS certification reduced from 330 minutes to 140 or 180 depending on which version of the engine the frame has.

Re: Getting a 787 back in the air after a diversion

#38

Post by jrockway » Sat, Jan 04, 2020, 6:36 AM UTC

sajomojo wrote: post #18

It just seems like a very bad idea that twin-engine planes can fly so far from an air strip. If the #1 engine had failed as well it would have been game over. There's no possibility of gliding a 787 for 2+ hours and hundreds of miles. If the FAA wanted to prioritize safety, it would still require the use of four-engined planes, as it used to for most long ocean routes. The desire to fly twin-engine planes over the oc…

ETOPS seems to have done pretty well. As far as I know, no ETOPS-certified twinjets have been lost due to both engines failing. There are a couple cases of the jet running out of fuel (the famous Gimli glider and Air Transat Flight 236), but that is going to be bad no matter how many engines you have. There are cases of airplanes flying into volcanic ash clouds and losing all engines; but more engines doesn't help you if the air around the plane kills engines. There are some poorly-engineered planes with 3 engines that have had a single-engine failure bring down the entire plane (United Airlines Flight 232).

ETOPS is not just some rubber stamp for a particular model of airplane that manufacturers self-certify (hello, 737 MAX debacle), but rather a process applied to (airframe, engine, airline). You have to service particular engines to particular standards to be allowed to fly ETOPS, and it depends on the airline. I could go to the store, buy a 777 and hire 4 ATPs and fly a 777... but I wouldn't be allowed to fly it ETOPS, for example.

All in all, the program seems massively successful to me. It saves fuel, which means cheaper flights and less CO2 being generated. That's a good thing. The main downside seems to be medical emergencies; I remember some stories about the aircraft that flew EWR-SIN... it has some special corpse compartments to stash away the inevitable deaths that occurred 9 hours away from an airport. (It had 4 engines, but engines don't perform heart surgery on passengers.)

The reality is that engines are pretty reliable. 2 is the right number.

Re: Getting a 787 back in the air after a diversion

#39

Post by jrockway » Sat, Jan 04, 2020, 6:39 AM UTC

sajomojo wrote: post #34

jacquesm wrote: post #26

Earlier quoted context omitted.

Contrary to your assertion the two engined craft are just as safe (or safer!) as the four engined craft because of changes in procedures. Fuel management, weather forecasting, general engine reliability, lubricant reserves are all different and much more stringent for a twin engined jet over water on a straightline route. The effect is the aircraft is less long in the air anyway which has a big effect on the risk cal…

Doesn't the fact that the twin-engine planes have to submit to more stringent ETOPS requirements mean the FAA believes they're less reliable than four engine planes?

2 engines of the type that they put on 4 engine planes are less reliable than 2 ETOPS-certified engines. ETOPS-certified engines (actually engine, airframe, airline combination) are going to be more expensive than engines where you have three extras next to them.

I could build a jet engine in my garage and the FAA wouldn't let me fly 270 minutes away from an airport with paying passengers on it just because I made four of them. Certification is always going to be important.

Re: Getting a 787 back in the air after a diversion

#40

Post by DuskStar » Sat, Jan 04, 2020, 6:39 AM UTC

sajomojo wrote: post #36

DuskStar wrote: post #32

Earlier quoted context omitted.

The only thing that a 3rd+ engine helps with in this context is uncorrelated engine failures. (Correlated ones - like "oops we used the wrong fuel units" or "that volcanic ash cloud sure is pretty" - are the same for two engines as they are for 4) These failures are really, really rare. A very conservative approximation would be one in 100,000 flights. (That would be once every other day in the US, for reference. Lik…

Except this ignores that the motivation was not increased safety but money. It does seem true that twin-engine planes can be quite safe but if Boeing/Airbus were motivated to create the safest possible plane, it would probably have four engines. I doubt the US President will be flying on a twin-engine plane any time soon. They'll choose the safest (American made) option. Probably an updated 747 model, no?

And my point was that motivation is irrelevant, and I would find it quite plausible that a two engined airliner would be safer than a four engined jet. Two fewer things to explode, after all.

The president flies a 747 for size and prestige more than safety. Safest option would be to recommission an Iowa and use it as an armed ocean liner or something and skip planes entirely. Or just to stay home.