Standby Pump light in cruise

[JRBarrett 3,070]

This is a very minor glitch.

I often see the hydraulic standby pump light come on while in cruise for no apparent reason. The system pressure on the number 2 side is right at 3000 psi when it happens.

In accordance with standard procedure, I put the standby pump switch to “auto” after all three engines are started, so that the electric pump will kick on to assist the mechanical pump on the number 3 engine if needed. (Or to take over completely in case of an engine 3 failure). 

On the ground, the standby pump might come on briefly after engine start if the number 3 engine is the only one running, and you put a heavy load on the number 2 system - perhaps by extending flaps while at the same time exercising the flight controls. Other than that, the standby pump should not come on in flight with all engines running normally - especially not at cruise, when hydraulic workload is low.

Also, prior to engine start, turning on the standby pump in the sim is pressurizing both the number 1 and number 2 systems. As you are probably aware, the standby pump only pressurizes the number 2 system in the real aircraft, so I assume this is a sim limitation.

The pump can pressurize the number 1 system on the ground, but this requires going to the aft service compartment and physically moving a valve from “Flight” to “Ground”. In this case, the standby pump will pressurize system 1 but not system 2.

That valve is typically used by maintenance to deploy the slats on the ground without having to start engines or hook up an external hydraulic service cart.

[scottb613 1,188]

Hi Folks,

Ditto...

Regards,

Scott

[ark 1,288]

4 hours ago, JRBarrett said:

Also, prior to engine start, turning on the standby pump in the sim is pressurizing both the number 1 and number 2 systems. As you are probably aware, the standby pump only pressurizes the number 2 system in the real aircraft, so I assume this is a sim limitation.

 

Not sure that is a sim limitation -- need to find out.

Al

[JRBarrett 3,070]

1 hour ago, ark said:

Not sure that is a sim limitation -- need to find out.

Al

Yes, the engine systems are indeed separate in the sim, and they are correctly modeled as to behavior. I was extremely impressed when I first purchased the aircraft to note that the pressure from the engine 2 pump only brings the system 1 pressure up to about 1800 psi. System 1 pressure doesn't rise to the full 3000 psi until after engine 1 is started, which is exactly how it works in the real aircraft. System 2 hydraulic pressure goes directly to 3000 psi after engine 3 is started, which again is exactly how the real aircraft works.

That was a nicely-done job of systems modeling.