View Full Version : 737 apu use during take-off/landing
cheapfuel
15th Jun 2003, 11:34
Assuming that I am correct in saying that the engine bleeds are normally closed for the takeoff and landing, and the APU is in use for the takeoff/ landing, at what point of time/altitude is the switchover to the engine bleeds after the takeoff. and the switchover from the engine bleeds during the approach commenced ? Thanks ahead.
Assuming that I am correct in saying that the engine bleeds are normally closed for the takeoff and landing, and the APU is in use for the takeoff/ landing, at what point of time/altitude is the switchover to the engine bleeds after the takeoff. and the switchover from the engine bleeds during the approach commenced ?
Normally the engine bleeds are open for takeoff and landing. For takeoff when more thrust is required THEN the engine bleeds are closed and APU is supplying the pack. When the first power reduction is made you can switch the bleeds.
We have the APU switched off for takeoff and landing, unless it is needed for something specific like if we dispatch with only one engine generator. Packs are also turned off to save engine life. The bleeds themselves are on, but there is no extraction. Packs go back on after thrust reduction (1500 feet agl).
There are two schools of thought of this - some say turn it on for take off some say turn it off. Most airlines have it off, so to speak!!
cheapfuel
16th Jun 2003, 10:21
Thank you TR and SLT-- am a little confused on one item though. If the packs are turned off for the take-off, what is pressurizing the fusalage. I understand that the plane is pressurized 200 ft below airport elevation, and the outflow valve is the main character in the controling of the pressure, but do not we have something from the packs to maintain pressure? thanks again
pancho
16th Jun 2003, 22:58
The normal procedure is a "bleeds on" takeoff. If you are performance limited a "bleeds off" takeoff can be used provided the APU is available. A "packs off" takeoff is definately not a normal procedure. As you say, the aircraft would depart unpressurised. The only time I have had to do this was to position a sick aircraft to maintenance due to a pressurisation problem with no pax on board. I cant imagine why or how a "packs off" takeoff could be used in normal ops. It certainly aint standard Boeing.:confused:
cheapfuel
16th Jun 2003, 23:38
Pancho--I got it now!! thanks alot
Fresca
17th Jun 2003, 04:19
SLT: I asume you are talking about the -200.
I was on the -300/-400, mostly -400 and we used bleeds and packs on for every takeoff. The only time I had the bleeds off was when departing from Canada, on a short rwy over the Atlantic, and then we used the engines bleeds off and the APU to power the left pack. (The X-Bleed was then off, and after T/O we put the R Eng Bleed on with the R pack, APU off, L bleed on). Therefore we were never unpressurized during this procedure.
It is in the Boeing manual.
Regards
SLT: I asume you are talking about the -200.
I was on the -300/-400, mostly -400 and we used bleeds and packs on for every takeoff.
I have used bleeds off on the B737-200, -300, -500 and -700.
Fresca
17th Jun 2003, 07:55
TR4A: A quick Question: What engines where on the -300? 3B1 or 3B2 (not 3C1 I'm sure)? As for the -700 What rating is on the engines there?
Regards
Fresca
SuperRanger
21st Jun 2003, 15:33
cheapfuel,
it is all written in the supplementary procedures in volume 1 under bleeds off takeoff. if i remember correctly, it's at 1,500ft.
SR