inflight AUX pump ops

[ASCTU744]

I believe I adressed this before but could the hyd AUX pump(s) be operated inflight after pulling some CB's? Looks like all you need is the GHB (AC & DC). Still looking into it

[B767300]

I tried this aswell in PSX, it should work right? I pulled the GRD SERV CB, started the APU inflight, confirmed GHB was powered and the required DC busses but nothing unfortunately.... I'd love to learn more about this, imagine having 2 additional pumps in the most critical HYD systems

[Hardy Heinlin]

The hydraulic system reads the in-flight status of the PSEU, and in this particular case it's the in-flight status referring to the CBs F22 and F23 on P7. These busses signal the in-flight status when certain PSEU sensors are in flight OR when the respective CB is unpowered. So when you pull such a CB, the PSEU will signal the in-flight status, not the on-ground status.

Don't expect you can toggle any in-flight and on-ground states by pulling a CB. A certain PSEU channel stays in-flight or on-ground when it's unpowered.

The design depends on the question as to which flight phase is the more important one for the respective device in case the PSEU is unpowered. E.g. to be able to extend the gear in flight is more important than to be unable to retract the gear on the ground. Landing with gear up is more dangerous than retracting the gear on the ground. So the PSEU channel that inhibits the gear retraction on the ground will signal the in-flight status when the PSEU is unpowered. When you pull that CB, the in-flight status remains. There are other devices where the logic is reversed, depending on the purpose of the device and which flight phase is the more important one.

[ASCTU744]

That tracks. The complexity of this plane blows my mind everytime😅 A pilot in a 744 British Airways doc said that the panel may look simple and intuitive but that the underlying systems are much more complex