Hydraulic pumps- on or off during turnaround??

[Centaurus]

737 Flight Crew Operations Manual
Normal Procedures -
Amplified Procedures
Copyright © The Boeing Company. See title page for details.

1 June 2007

Are you sure the items published as FCOM procedures are exactly Boeing and nothing else added? Seems to me a fair amount of company initiated material added when compared with the "original" untainted Boeing FCOM?

[luvly jubbly]

On the 73s I used to fly; Electric hydraulic pumps off. All fuel pumps off except for fwd left if req for apu.

For 757/767; all fuel pumps off, hydraulic pumps off (except engine driven pumps).

http://www.b737.org.uk/nnp.htm

http://www.757.org.uk/sops/sop9.html

[rubik101]

As has quite rightly been pointed out, many, if not all FCOMs are indeed altered to accommodate each airline's peculiar requirements.
They are however, submitted to Boeing to obtain a 'No Technical Objection' certificate from their Flight Ops dept.
The procedures quoted above reflect a turn around on a multi sector day, 4 to 6 flights, with minimal wasted time on the ground. The 'Secure' checklist is used at the end of the day after the last flight.
The greatest wear on any pump, be it electric or hydraulic, is that incurred during start up. Multiple starts causes far more wear than constant running.

[Mr.Brown]

The 757 and 767 have much better indications on their hydraulic systems than the 737CL at least.
The 737CL has no flight deck indication of the reservior pressure therefore I would check the reservior pressure in the wheel well, before running the electric pumps on the ground, with no bleed air on, to avoid cavitating the pumps..

[rubik101]

Why would running a pump with no accumulator pressure cause it to cavitate? Even if the accumulator pressure is zero the pumps will still pressurise quite safely. The accumulator is downstream from the pump.

[smudgethecat]

I think your getting confused between accumulator pressure and resv header pressure rubik , two very different things.

[blue belly]

I'd really appreciate to hear from some 757/767b operators- any out there?

[Old Fella]

Transit configuration

Rubik101, thank you for the checklists, however I still wonder at the reasoning.

[BOAC]

Cannot help 'blue belly' with the 75/6, but it is common practice on the 737 to have the pumps on for the walk-round to check for leaks etc and rudder position. It then becomes a practical matter of 'how long before next the walk-round' and 'how long before we do the cockpit prep' for the next sector as to whether they go off in the shut-down or stay on. EG - I suspect Ryanair don't bother to turn them off. I don't on t/rounds of less than 45 mins, when I'm normally out of the seat PDQ, with fuelling, finding the agent, checking my bag has not been off-loaded in bongo-bongo land and beating the next rain shower in mind.

[rubik101]

Smudge, you are quite right, however, the reservoir does not need to be pressurised with bleed air before the HYD pumps are run on the ground. The positive air pressure is to prevent foaming when at high altitude.

[CEJM]

Rubik101,

Sorry, but you are partially wrong. The hydraulic reservoir needs to be pressurized before running the pumps on the ground.

Unfortunately, I can not copy the info into this topic (no idea how to do it ) but in the B737 Maintenance Manual it clearly states that you have to pressurize the system before running the pumps.

[rubik101]

CEJM, are you saying that the HYD pumps cannot be run on the ground unless the APU is running and the bleed system pressurised?
If you are, it's news to me and I have flown the 737 for over 20 years.

[Denti]

Nothing in our FCOMs about that as well. No requirement to pressurize the reservoirs first, neither in classics nor NGs.

[Back Seat Driver]

re 737, long time since I flew one and am happy to be corrected, but I think the HYD pump switches require electric power to turn and maintain the HYD pump off (unpowered the pumps will be on by default). This makes no difference when the aircraft is put to bed for the night, except isn't it then redundant to turn the electric hydralic pumps OFF once electrical power is removed from the busses.

[stilton]

The potential safety aspects of injuring ground personnel outweigh any other
reason to leave (especially) hydraulic pumps on during any turn around.

[aerostatic]

737 Flight Crew Operations Manual
Normal Procedures -
Amplified Procedures

Are you sure you are using a completely Boeing standard FCOM? It doesn't look like it to me. Many companies pay Boeing good money to incorporate their own SOP's into the Boeing FCOM.

Edit: Sorry I see Centaurus has already queried this.

[CEJM]

rubik101, we miht have crossed wires at the moment.

Before running the hydraulic pumps the reservoir has to be pressurized. However this does not mean that the APU has to be running and the bleed system to be pressurized.

During maintenance we have to release pressure from the hydraulic reservoir by means of an depressurization valve. This will remove all pressure from the reservoir. After this has been done you need either bleed air to provide pressurization or an external air supply. Runnig the pumps without the tank pressurized increases the risks of cavitation.

In normal day to day operation of the aircraft the pressure on the hydraulic system should be maintained be a check valve in the pressurization module.

So for a pilot, as long as the tanks have not been depressurized by maintenance you can run the pumps on the ground without the APU or the bleed system pressurized. However may the system have been depressurized by maintenance or a faulty check valve then the system needs to be pressurized before runnig the pumps.


Leaving the hydraulic pumps running on the ground (when not required) is bad practice and puts people in danger. Yes, I agree you will be able to see a leak quicker. However, several times in my career we had such a small leak which was only evident by a fine mist in the wheelwell (and declining quantity indication in the flight deck). So the poor bugger going into the wheelwell has the hydraulic fluid all over them. Not a good practice and something which should be avoided.

[smudgethecat]

Getting back to the original post which refered to the 757/767, i had a look at the 757 FCOM last night and it clearly states the hyd pumps and the boost pumps should be selected off, so perhaps that settles it (or maybe not)

[blue belly]

Getting back to the original post

Thks Smudgethecat- some companies do things which are not manufacturer SOP, and I am wondering if there are some 757 or 767 operators who do leave the pumps running during turn arounds.

[smudgethecat]

Hi BB, maybe there are, however as i said previously we look after a fair few 757/767 operators from a variety of countries and ive never known any crews carry out this procedure, i cannot really think of any reason why you would wish to do so , however you never know