EASA 66/ assignment help needed from the pro's.
 

Hey guys. I'm currently doing an assignment on the hydraulic system of a Boeing 757. The following question seems vauge. wondered if anyone would agree:
Q: The pilot reported in the technical log defect column as follows: "number one hydraulic system showing low pressure. vibration felt through airframe. Pressure indication fluctuates between 100 and 1000psi.
[B]Describe the procedure you would follow to isolate then rectify the fault?[B]
Seems to lack in information to me, I would assume the aircraft was in normal flight when the fault arised. This i guess would indicate the EDP was vaulty, not the ACMP. yet the gears must still be turning (hence vibrations and pressure fluctuations). I thought maybe one of the EDP pump gears had shattered, or excessive bearing wear, putting the pump out of ballance, resulting in the vibrations.
Does anyone else have experience with this fault? would my diagnosis seem reasonable? If the EDP was faulty, swould the whole unit be replaced, or just the faulty bearing/gear?

regards to all,

Toby.

I would say exactly the same. Except I've never seen a broken edp causing vibrations. Maybe the vibrations come from a quick up and down movement of the pressure, resulting in some control surface flutter? (eg some spoilers on left system only?)

Sounds like that could well be the case. thankyou.

What drives the pump?

pump cavitation can cause loss of pressure with associated airframe vibration.

I agree Rivet,

Often caused by a lack of reservoir pressure which explains why the pressure fluctuates even though there are 2 system pumps (EDP/ACMP)

The reservoirs are automatically serviced with 25-50PSI air from engines (or APU if engines not running). If this is not occuring wouldn't you have the res pressure message on eicas?

If cavitation can indeed cause vibrations, I wouldn't search further for an explanation.

Thanks too all, that has certainly got me thinking.

Always go to Maint Manual. First i would check the case drain filter for material, if any found replace the pump. Then check pump press filter for contamination. Sounds like the compensator cartridge has failed for the flight controls