Question for B737NG rated pilots. [1]

[StudentATP]

Hi everyone,

from what I know, if Hydraulic system A leaks and fails, half of the flight spoilers dont work, Nose steering dont work, etc... because there is no fluid there to move them.

My question is:
Let say engine #1 fails and system A is working normally, engine driven pump is therefore inop but AC motor driven pump continue to operate, does the flight spoilers, nose wheel steering, autopilot A etc...still function?

the flow capacity of AC MDP is comparatively lower than the EDP, so I was wondering if the system functions would be afffected.

Thank you in advance

[BOAC]

What does the QRH say? How many 'Low Pressure' lights are lit? Where is the leak? Which checklist will you call for?

[STBYRUD]

Oh, they all work, just a tad slower. The QRH for example will tell you that you can expect asymmetric thrust reverser deployment during landing, the left one in your example will take considerably longer to deploy. The landing gear also takes long to retract, thats why there is the Landing Gear Transfer Unit that uses System B fluid and pressure to raise the gear in case of a failure of engine one during takeoff and the initial climb.

Oh, and I am assuming ENG 1 LOW PRESS, nothing else.

[EW73]

Also I think you'll find that the 737NG FCOM volume 2 states (correctly) that, with a high service demand on that hydraulic system (with the EDP inop), the 'low pressure trip' for the A autopilot may occur momentarily, dropping out the autopilot, but can be immediately re-engaged.

EW73 :\

[Avenger]

I think you answered your own question " System A is working normally" , as observed, slower than normal deployment times can be expected for the TR.

[StudentATP]

thank you STBYRUD.

I guess the purpose of Landing gear transfer unit and the PTU is to speed up the retraction of gear and the extension of flaps/slats respectively, when system A & B are slow respectivaly. yes?

StudenATP

[StudentATP]

Thanks EW73

dropping out the autopilot A? that is not cool....

[STBYRUD]

Basically - the landing gear is operated by system A only, and because a failure of engine 1 would also remove the output of the engine driven pump it would take too long to raise the gear.

[BOAC]

dropping out the autopilot A? that is not cool... - why would you be using A/P A?

[excrab]

Maybe because they dispatched with autopilot B u/s, in accordance with the MEL.

[STBYRUD]

In any case, as previously mentioned, its pretty unlikely that it will disengage due to low pressure, and even if it does you can reengage it right after. It might happen if you rip out the flight spoilers during descent, thats a pretty significant load on the hydraulic system.

[BOAC]

Maybe because they dispatched with autopilot B u/s, in accordance with the MEL. - hmm! A useful contribution indeed. Yes, maybe they has a No 2 engine failure, or a wing fell off? I'm looking at post #1 - which one are you?

[excrab]

BOAC,

Sorry if I ruffled your feathers. At the three 737 operators I have flown for it was SOP for the captain to engage autopilot A and F/O to engage autopilot B.

Student ATP commented that auto pilot A droppping out was not cool, and you responded to it by asking him why he would be using autopilot A. That was nothing to do with post number 1. I was answering your question with a perfectly reasonable answer. Alternatively he could be a captain training on a new type in which case using autopilot A would be perfectly normal.

Now two reasonable answers to your post, which was actually totally irrelevent to the original question.