B73NG turning on Elect Hyd pumps

[galdian]

Hi all
Came off classics and due "weaker" APU's were taught have a break of a couple of seconds to avoid electrical "shock" when turning on the electric hydraulic pumps.

Carried on the procedure to NG's, now striking newbies most who do same but some don't.

Per Boeing procedures are there any references for NG ops Vs Classics??

Thanks, cheers.

[Jonnyknoxville]

I don't think so , you just need to tell the new guys , especially when at 20000 feet , they switch them off instead of the anti ice .

[alcan60283]

Probably not the worst idea to continue your habit of waiting. You could theoretically create a large enough spike turning all the pumps on at once. I'll look into if there is protection for that

[UAV689]

I have seen them turned on and off quickly, and the elec pump cb tripped.

Also seen it when the ground staff pulled the ground power out, and power tripped off, then the Apu was put immediately on the buses (apu was running but not yet powering electrics) and that popped the elect pump as well! Both on an 800 series.

[73qanda]

I’ve got about 7000 hrs in a combination of -300’s, -400’s, 700’s and 800’s and have never read anything about a pause between the two. I’ve never noticed anyone pausing either. I’ve never seen it cause a problem.
Not saying it’s not a good idea to pause, just relaying my experience on the subject for info/ perspective.

[galdian]

Hi all

Thanks for the replies, sounds like one operators thoughts based on carryover from previous types or experience or...?

On a tangent I have a place on solar power/batteries, they state the size of the inverter must consider the STARTING demand of an electric motor (eg water pressure pump) rather than the RUNNING demand, starting can cause an electrical spike up to 7 times the running demand.
Assuming similar for elect hyd pumps the pause makes sense if not a 'boeing' thing.

Cheers.

[tdracer]

Originally Posted by galdian

Hi all

On a tangent I have a place on solar power/batteries, they state the size of the inverter must consider the STARTING demand of an electric motor (eg water pressure pump) rather than the RUNNING demand, starting can cause an electrical spike up to 7 times the running demand.
Assuming similar for elect hyd pumps the pause makes sense if not a 'boeing' thing.

Cheers.

That is true of most electrical motors - there is a big inrush current when started that is much greater than the steady state running demand - usually at least twice.

[Centaurus]

sounds like one operators thoughts based on carryover from previous types or experience or...?

If it was that vital for technical reasons to pause before turning on each electrical hydraulic pump, then Boeing would revise their checklist to warn of the requirement. For example the Boeing 737 Classic QRH on Loss of Both Engine Driven Generators. It states:
Bus Transfer switch....Auto
Elec Hyd Pump switches (both),,,,,,ON, one at a time.

So much personal opinion is taught as a technical fact that you don't know where the bulls#t starts and stops

[fdr]

Originally Posted by Centaurus

So much personal opinion is taught as a technical fact that you don't know where the bulls#t starts and stops

True, however there is also common sense. Recall a certain A340-300 out over the GAFFA that the FO decided to balance the fuel tanks, and used all of his fingers at the same time to switch the fuel system configuration, which was fine, except he got the hydraulic switches instead. Not a big deal even then, until the pumps were all turned back on at the same time, but with the lag of realisation, where the FCC's had already demanded full deflections due to the non response to the slight corrections that were required. With hyd pressure, people went flying across the cabin in an untidy heap, with many injuries. Flicking multiple switches at the same time is great if your mind parallel processes, which the human mind doesn't necessarily do well at all. Back at the beginning of the B777 program TBC's own trainers were averse to multi switch flickers, even though the preamble, and procedures did not speak against the practice. Times change, but common sense has a place at the table.