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
