The parking brake is on the No2 system, with a nitrogen charged accumulator located in the right wing root. According to most SOPs, minimum pressure in the No2 system before engine start is 500psi, anything below that then the system pressure must be restored by operating the manual pump in the right engine nacelle. That is why it is normal to start the No2 engine first on the Q400. The hydraulic pumps are driven of the reduction gearbox, the APU supplies DC power and Air only. The reason most SOPs use 500psi as minimum pressure (or 1000psi if you choose to start the No1 engine first) is because it is possible to have indications of pressure in the No2 system below 500psi but that is most likely residual accumulator gas pressure, and brakes will not function. So it is quite easy to foresee a scenario where an aircraft parked on an incline with little or no accumulator pressure will begin to roll when the chocks are removed or someone cycles the parking brake to test it and unwittingly depleting the remaining pressure.

Whilst aircrew (may) know where the brakes are I wouldn’t expect your average handling agent or ground crew to necessarily know where or how to operate.

If the residual hydraulic pressure or accumulator residual had fallen to an ineffective level then the aircraft would have rolled against the chocks with the slope at the first opportunity - making them very difficult to remove against the weight of the aircraft...?

Does the Q400 not have a standby hydraulic pump that works of the batteries? so if the engine driven pump goes u/s there is no back up from a DC pump? why could they not switch on the batteries (or plug in an GPU) then turn on the standby pumps and charge up the system? just interested as I have never flown the dash.

Video, as the previous Facebook post appears to no longer work.

https://ukaviation.news/cctv-shows-m...-regional-jet/

Engineers perform ground engine runs every day without the need to involve pilots.

The Q400 does not have a DC pump. There is an AC pump in the no1 system called the SPU (standby power unit) and there is a PTU that pressurises the no 2 system from no 1.
The normal ground power is DC on the nose but AC can be connected on the right nacelle.The usual way to top up the parking brake is with the hand pump in the right nacelle.
If the maintenance guys had just done a "Line Check" (75hrs or 10 days I think) then the brake pressure would have been depleted to check the N2 charge in the accumulator (500psi). The hand pump needs to be used to top up the pressure again.

Cheers for all the technical info on the Q400. Swiss cheese central again.

Well you know very little about aerospace structures or your having a Steffi Graff. The latter prehaps.