when do you turn off enginees

Not really sure what you mean . You turn the engines off as soon as you get to the gates and you are in the correct position, but you leave the APU running whilst the passengers get off the plane I think. Could be wrong though.

Certainly after landing and not before....unless you have huge flames coming out of them!
Seriously, as soon as possible once you are at the gate and completed the "Shutdown" checks. APU is usually online in most jets for those without power is on the batteries or ground power.

I usually shut 'em down after I've turned everything else off i.e. avionics, radios, etc. I wait until the fans have stopped before I turn off the strobe and beacon. ---- All this is after I'm at the gate. In four engine craft, I sometimes shutdown the outboard engines after I have cleared the rnwy and started taxiing toward the gate.

Simple question. What is the APU? I have an idea what it is but I just want to be sure.

Auxillary Power Unit.

It's what makes the stuff go "beep" when the engines are not running.

thanks for all of that info. sorry i didnt make my self too clear in the beggining, but i was in a rush at skool. but i noticed someone mentioning outboard engines. what are they, and where are they, plus, same for the inboard engines. thanks alot everyone

Outboard engines, on a 747, are engines 1 and 4, inboard are 2 and 3. I would NOT recommend shutting down 2 engines and taxiing to the gate with only 2 on the 747. You can do it on the MD-88, but thats it. not the 737 either. reason being, it takes too much thrust to push the 747 with only 2 engines active. and It's loud, and a strain on the 2 running engines, cause they have to do more work

thanks fem, i get it now

The 747 can CLIMB on 3 engines so I don't think taxiing on the ground on two engines would be a problem. Theoreticaly; it is more efficient to taxi on 2 instead of 4 engines, if you have four because a jet engine is more efficient at higher power settings than at low power settings. I gleaned this info from a design proposal for a centerline thrust twin jet that had a large engine for cruise and a small engine to assist in takeoff and climb config. In cruise the large engine's N1# was intended to be around 96%. Evidently, it has been found that one engine at high power settings is more efficient than two engines at lower settings giving the equivalent thrust. This design was tabeled because the FAA had problems with the small engine start-up difficulties at altitude.

huh, did not know it's more efficient with 2. Thanks!