Pressurizing the hydraulics

[Kristian17]

when you turn on the electric system during pre-flight on most airliners, if I am right, one hydraulic system pressurizes. Do you have to ask ground for permission to pressurize the hydraulics for this or do you only ask permission during engine start-up when the remaining systems pressurize?

Thanks for your help
Kristian

[Jet II]

You don't ask for permission to start any hydraulic pump - as for how many systems are presurised that is variable depending on type.

[PRNAV1]

Qoute...

[Jet II: You don't ask for permission to start any hydraulic pump - as for how many systems are presurised that is variable depending on type..]

is un-true...when an aircraft is parked up with engines shut down, the hydraulic sytem(s) will be unpressurised. un-less of course the system is being pressurised by the electric driven pumps, which are normally there for back up.

once we start the engines , after ATC clearence and ground clearence, the hydraulic system(s) will pressurise accordingly but in sum cases we may need to pressurise the system(s) at the gate, using the electric or engine driven pumps.
ground clearence will need obtaining for a number of reasons...
examples being them working on landing gear doors, flt controls, hyd system itself....etc.
(we don't want to take any limbs off if we can avoid it...)

so i hope this clears things up abit

[Kristian17]

Thanks for your help with that!

In what circumstances would you need to pressurize the hydraulics at the gate? Is it only if you wanted to start the engines before push back?

See you
Kristian

[expedite_climb]

My SOP on the 777 is to pressurise hydraulics on stand before pushback.

For sake of clarity - you asking for permission to pressurise from the man on the headset downstairs - not the ground controller !

[bafanguy]

The issue of pressurizing hyds at the gate has to do with the possibility/probability of squashing someone who happens along and sticks some part of himself in harm's way as you pressurize.

If you are operating a narrowbody that sits close to the ground and has "stuff" drooping, you'd better be careful ( 727 Krueger flaps...any open gear doors, drooping TE flaps on any type acft ).

We had mechs killed in these situations when727 LEDs snapped closed after they had "inserted" themselves into the leading edges for some purpose and someone else turned on a "B" pump and opened the gorund inteconnect for yet another purpose without coordinating with all concerned. At least it wasn't a crewmember who did the deed but a fellow mech.

Unless you fly some big, tall airplane, you better be darned careful about pressurizing hyds at the gate without letting EVERYONE know what you're about to do.

The most dangerous time to operate an airplane is from the time the main gear touches the ground until the main gear leaves the ground again.

[Intruder]

I fly big, tall airplanes, and still get clearance from the mech on the headset before pressurizing hydraulics!

For those who don't know airplane sstems, electric hydraulic pumps are not activated every time electrical power is on the airplane. There are separate switches for each pump, and they are turned off immediately after engine shutdown. They are not turned on until said clearance is received in the midst of the Pushback/Engine Start checklist.

[18-Wheeler]

[Jet II: You don't ask for permission to start any hydraulic pump - as for how many systems are presurised that is variable depending on type..]

is un-true...when an aircraft is parked up with engines shut down, the hydraulic sytem(s) will be unpressurised. un-less of course the system is being pressurised by the electric driven pumps, which are normally there for back up.

Agreed, it's extremely dangerour to pressurise the hydraulics on the ground without positive clearance from the ground crew. As mentioned above, you can get people killed by doing it.

[Jet II]

OOPS

When talking about asking 'Ground' I assumed you were talking about Ground ATC.

Although having said that, not every flight crew asks the guy on the headset if they can pressurise the hyd systems.