C-680 Experience

[DanielH]

This won't be cool for many of the jet guys but for a lowly piston driver like me, it was very cool.

I was at the airport after work just to see what was going on and saw a few mechanics working on a Citation Sovereign that had an EICAS message (I think that's what its called) for a low hydraulic pressure on the left engine. The weird part was that neither pilot saw the pressure drop into the caution range and no master caution was triggered. Well the mechanic was nice enough to left me start the APU and the engine (surprisingly simple) and watch while one mechanic tapped on the sensor to try and replicate the problem. They also tried to go from idle to opening the thrust reversers and deploying the speed brakes at the same time to try and load up the hydraulic system. Mechanics were not able to replicate the problem with any scenario. The hydraulic pressure read-out and the EICAS message come from different sensors so they were attributing the problem to one of the sensors not being calibrated correctly. There's already a new sensor on a courier flight tonight so it is getting replaced no matter what .

That's the way I understood it from how the mechanics explained it, please correct me if I'm wrong . Probably the norm for a lot of you, but very cool for me. Reminds me why I love aviation.

 

[Everskyward]

The dreaded "could not duplicate"...

C-680 can sometimes be a hypochondriac.

Also, there shouldn't have been a system pressure drop even if the left hydraulic pressure was low or even zero. The pump on the right engine will keep the pressure up. Of course that's if both engines are running.

 

[DanielH]

For the ground run it was just the left engine running. Only report mechanics had from pilots was "had a left engine low hydraulic pressure message for about 5 seconds on landing roll out". I guess having both engines running would explain why the system pressure on the read-out didn't drop...duh.