PDA

View Full Version : Electrical power for B744 engine start?


kuobin
3rd Jun 2006, 16:20
Hello:
From our company B744 procedure that requires us to switch off all of galley power and inflight entertainment system before engine start if only one electrical power source available. (one APU generator or one external ground power),I just unable to figure out do we need that much of electrical power to start engine.because we use pneumatic starter to crank engine and igniter will not drain too much current.isn"t?:rolleyes:

gas path
3rd Jun 2006, 21:03
It's not for the engine start as such, more to guarantee a good stable source during the engine start, galley power, and IFE even more so are power hungry and the last thing you want is the power dropping offline at a critical point in the start sequence.

Denzil
3rd Jun 2006, 22:33
As an example of the galley/IFE loads, any A346 guys have a look at the APU gen on the ground with IFE etc in use, gets up to 90% of capacity.

Oldy
4th Jun 2006, 13:45
Hi K, from memory it is to do with load shedding after engine start. If one engine generator comes on line first, knocking off the ground/APU, even if you start two engines at a time, it will load shed some IFE and galley power which then has to be re selected manually after more than one engine generator is available. It is just messy this way round so to avoid the problem switch off IFE / Galley first.

Swedish Steve
5th Jun 2006, 19:00
The B744 has two ground power sockets. While one is adequate for normal use on the ground, part of the start procedue is to turn on the hyd pumps. These use a lot of AC power and it is a good idea to reduce the load on the ground power before turning on the hyds. The B777 is even worse. If possible it is a good idea to start one engine, and get the generator on line before switching on the hyd pumps. It can be embarrassing to turn on the AC hyd pump, and the power trips off!