B73 Next-Gen APU useage???

[Skytrucker87]

Gents, I am a bit out of touch with these modern contrivances so please please would any 73 next gen blokes answer a question for me.

How long do you run the APU for and at what stage do you shut it down? Am I correct in thinking that it could be used to top of climb to provide services such as pressurisation? How much benefit would that provide in fuel saving and engine performance?

Easyjet and Air Europa pilots answers would be extremely welcome!

The last aircraft I flew burned solid fuel and had an outside toilet so please forgive the inquisitiveness of an old-timer!

Cheers

Trux.

[seat 0A]

I fly the -800 and -900 series.
Since most major airports these days require that you use the APU for as little time as possible (noise), we normally start it just prior to push-back / engine start. Before taxi-out we switch it off again. During taxi-in, we only start it, if the ground power supply at the arrival gate is known to be either absent or slow to connect.

One can use the APU to aid in cabin pressurization, but that is only used if required for performance reasons during take-off. That way you can switch off engine bleed and get more thrust from the engines.

Hope it helps

[Oceanic]

Inflight-APU bleed + electrical load: max alt 10,000ft
Ground Only-APU bleed+ electrical load:max alt 15,000ft
APU bleed: max alt 17,000ft
APU electrical load: max alt 41,000ft

Due to excessive time spent on ground we have double the APU hrs that we have on engines! (BBJ2 ops)

[alexban]

due to some cases of generator failure now our sop demands to keep the apu runing until after takeoff( but not used for electrical or pressurization,just as a backup)

[seat 0A]

Rather strange SOP, if you ask me.
What`s so urgent about a generator failure during T/O, that you would want to have the APU on standby constantly. An APU start only takes about a minute.
In my company I haven`t read anything about problems with generators on the NG.

[mono]

The answer to the question will be vague.

APU usage depends on company SOP and little else.
The useage described by seat 0A would be very expensive. It has been calculated that operating an APU for less than 1 hr is counterproductive as savings on fuel are more than offset by increased APU maintenance costs.

My company uses the APU from taxi in 'til taxi out. Some airports or SOP's may require the use of APU for airconditioning on take off (for max available power). The last flight of the day usually does not use the APU on the final taxi in.

Use of the APU in flight will not save any fuel (although it will provide a little more available power) as the APU will burn some fuel too (50 kgs an hour with 100 kg/hr for the first hour seems to ring a bell)

[Popolama]

i agree with seat 0A when he says it s strange to keep the APU running from taxi till after t/o.but imagine you were on a dark night takin off and BLOUP ! suddenly loss of both gens,well.1 min will be forever.:cool:

btw,we keep the APU runnin for 1 min before using bleed after start,as well as 1 min w/o bleed before shuttin down (733) garett

[free and zero]

Hmm, the chances of a double gen failure,

Depends on sop. N/G ac no need to run for one min, as it will do that automaticaly. it will run both pack`s on the ground (as you probably know). :ok:

our paticular sop, requires it will be switched off on the ground but as always capt descression. in some cases it would be wise to leave it runing. the problem then is the chance one forgeting it is running. :\
the N/G apu is a beefed up version of the E/G models

:ok: