Um, been cruising at FL380 in my 777 for 30 minutes and just realised my APU is still running. Oops. My bad. Is that a major in real life or no biggie? In the sim I just turned it off and carried on.

apu has designes to run in any condition, especially in a dual engine failure at cruise or any other situation : engines generator fail or ... but apu run with fuel left tank if apu run for long time in flight you will have a fuel inbalance and apu warm in a long time period its a risk of apu fire or apu fail just that its a mistake for you , no a big mistake but a mistake with other one and other one and other can cause a crash a perfect flight its a secure flight, a good flight its a good flight but with cumulative mistake can cause a crash its a riski flight

I think there is a max allowed speed for use of apu. The air intake sticks out of the airframe after all. But I am not sure... ;-)

A running APU consumes fuel, but other than that it's no big deal.

 

Heck, I'm pretty sure it happens every day somewhere around the world that a real crew forgets to turn the APU off after starting the engines...

You'll probably turn on the APU after a single engine failure to regain some safety margin. And your flightlevel on SE could be pretty high (not as high as FL380, though). Doesn't look like a big deal to me if it's running inadvertently during normal operations.

You'd only use more fuel, both due to the APU actually burning it, and due to the extra drag created by the APU intake sticking out of the fuselage. If you really, really, really want to get pedantic, the APU actually does provide a tiny, insignificant, VERY neglectable amount of thrust.

Also, during some (all?) ETOPS flights, keeping the APU running is a requirement.

I'm sure other, more knowledgable, forum members will be able to chime in here.

 

Also, the APU intake will of course fail at a certain speed, but that speed is probably designed to be FAR outside of the normal flight envelope. Why? Because it's quite a good idea to be able to start the APU right away if you have a dual engine failure at whatever speed you're flying.

Thanks for the info guys!

yeah, no biggy.

But waste of fuel yes.

 

Its not even in the checklist (well...I guess that might be company dependant).

 

APU - ON during ETOPS is only required if you are dispatched with certain malfunctions according the MEL (minimum equipment list).

Just guessing here.....but with for example a failure of the electrical backup system, you could still do an ETOPS flight as long as you keep the APU running.

A running APU consumes fuel, but other than that it's no big deal.

 

Heck, I'm pretty sure it happens every day somewhere around the world that a real crew forgets to turn the APU off after starting the engines...

I really hope that's not true, because then what else might they forget about? Once (in the sim, a fighter I think), I forgot to retract the gear, I hit about 400 knots and heard a very foreboding sound. Then I saw the green info text message saying: "Your landing gear has been stripped off." oops.

I really hope that's not true, because then what else might they forget about?

 

Pilots are humans and forget many things, not only the APU. That's at least how your system has to be designed. You can't expect to tell someone: "Hey, as long as you don't forget this one thing, everything is good. If you do forget it, the plane will crash" Because eventually, someone will forget it and a plane will crash. The thing is that for those items that are really important, there are several "lines of defense". If you forget to set the flaps for takeoff, first there's a standardized flow the pilot performs as a routine, then there's the checklist and on top of that there's the "Takeoff Configuration Warning System", that will trigger an alarm if you attempt to takeoff without flaps.

 

Since the APU is something you actually "might" want to leave on the whole flight (for example, during ETOPS operations), there are no lines of defense for that on many aircraft. On some there's a "status message" on the EICAS reminding you that the APU is running.

Guys, you don't need the APU for ETOPS in the 777, unless some very specific circumstances happen (as Rob said, MEL or failure enroute)

 

You probably remember that from the 737 discussions, where it is indeed common to have APU on for ETOPS (but also, not neccessarily always the case).

That has to do with the fact that 737 was not designed as intercontinental craft.