Manual conflict! - Setting Hydraulic Demand pumps

[tf51d 284]

I was watching a youtube video showing checklists, and noticed the demand pumps were set after pushback, instead of during the Before Start Check. I was just about to comment on it, but checked the Checklist PDF provided, with the 744X. which verified, it should be during the Before start check. Then I looked in the Normal Procedures PDF, and that one indicated, it is done at Pushback (After the Before Pushback check but before Engine start.). So my question is, which is the correct procedure, the one in the Checklist or the Normal Procedures? Or does it matter?Thanks!

[Allan Burek 3]

Depends on which pumps. Without systems 1 and 4 you will lose body gear steering and that can be a pain for the crews pushing back the aircraft. Also, system 4 is your primary braking system, hence the aux electric pump on that pylon. With that being said, its probably a good idea to have 1 and 4 demand pumps set to on prior to brakes released, however dont run a pack at the same time as engine start with 1 and 4 aux hydraulic pumps because of an overdemand condition of the APU bleed air system.

[Guest jumbojock]

Hi TomBefore start, No 4 ADP is selected to AUX, as it provides brake pressure as well as stopping fluid transfer between the hydraulic systems. If push-back takes place before No 1 engine start, place No 1 ADP to AUTO to allow nose and body gear steering.I don't know what the PMDG manual says, I'll have to have a look at it.David "jumbojock" Robertson

[Qavion 19]

"Without systems 1 and 4 you will lose body gear steering and that can be a pain for the crews pushing back the aircraft."Body gear steering only uses System 1 ;)"however dont run a pack at the same time as engine start with 1 and 4 aux hydraulic pumps because of an overdemand condition of the APU bleed air system."Not sure what you mean here.... You are not likely to overdemand the bleed system with one pack on. In fact, it is standard procedure on a lot of airlines to prevent duct pressure shock (where the bleed system software hasn't been updated).... and didn't you just say that the Aux pump/s were electric, not pneumatic? So that will have no effect on the bleed system.Cheers.Q> イアン

[claviermichel 0]

HI guys,Thanks for the very instructive and informative lecture but I think Tom's question was:quote which is the correct procedure, the one in the Checklist or the Normal Procedures? Or does it matter? unquoteCould you please shed some light on the question asked?Best regards

[tf51d 284]

I think by the answers given, they are saying it should be done at the Before Start Checklist, which is what I always thought. I guess you can also do it within the before pushback check, but setting it after the before Pushback seems to suggest setting it during or after pushback, which would have a negative effect on steering and braking as the earlier posts indicate.

[Qavion 19]

"but setting it after the before Pushback seems to suggest setting it during or after pushback, which would have a negative effect on steering and braking as the earlier posts indicate."The pumps should be set before you release the park brake for pushback for the reasons mentioned above. Therefore, it should be part of the before pushback checklist. Having said that, some airlines modify their checklists because they think they know better than Boeing　;)Why not carry out the prestart checklist before pushback, just to make life easier?Cheers.Q> イアン

[Guest jumbojock]

"Having said that, some airlines modify their checklists because they think they know better than Boeing　;)"I know exactly what you mean!David "jumbojock" Robertson

[Guest ColdBear]

Q,This is ALL done prior to pushback and startup.Boeing procedures:Obtain clearance to pressurize hydraulic systems and start engines.Hydraulic demand pump 4 selector ................................................. AUXVerify SYS FAULT light extinguished.PRESS light remains illuminated.HYDRAULIC panel...................................SetHydraulic demand pump 1, 2, and 3 selectors - AUTOVerify demand pump PRESS andSYS FAULT lights extinguished.Also,Pack control selectors ........................... SETAll packs may be off or one pack may be on for engine start.Hope this makes it clear,Martin

[Qavion 19]

"Q,This is ALL done prior to pushback and startup."Well, that's the way we do it on our aircraft, but I can't vouch for other airlines.... actually, I think it was Tom who had the problem with checklists(?) ;)United, for example, has a reputation for changing checklists/operating procedures.... e.g. setting V2+10 in the MCP window, etc. Some airlines try to standardise checklists across a varied fleet, but this seems to be an insult to pilot's intelligence and may be counterproductive.Cheers.Q> イアン

[Guest ColdBear]

Q,Like I wrote this is actually taken from ILFC so it may not be exactly Boeing procedures.regards,Martin