Global Express hydraulic Power Control Units

Effectivity: Global Express/XRS/ 5000/5000 GVFD/ 5500/6000/6500 aircraft

ATA 29

Bombardier wishes to remind maintenance personnel of the information that can be found in the AMM to help with quantifying hydraulic leakage beyond the design specifications.

By design, hydraulic Power Control Units (PCU) are self-lubricating assemblies. They may show evidence of hydraulic fluid wetting/leaking on the external surfaces and moving parts during dynamic cycling. The wetting/leaking can also occur when the PCU is in static mode. Fully functional PCUs may be incorrectly diagnosed as leaking and removed from the aircraft when in fact they are well within the design and test requirements for wetting and leaking allowances.

The in-service component leakage rates are published in the BD 700 AMM Task 29-00-00-790-801. The information listed relates to components, seal functions, seal types and the limits of leakage rate for each given area.

Each PCU has a leak test task in the AMM and are referenced below:

AILERONS                                          AMM TASK 27-11-25-790-801

RUDDER                                            AMM TASK 27-21-13-790-801

ELEVATORS                                      AMM TASK 27-31-21-790-801

MULTI FUNCTION SPOILERS          AMM TASK 27-62-01-790-801

GROUND SPOILER                           AMM TASK 27-63-05-790-801

Important note: One of the first steps for operators is to ensure the PCU is cleaned from dirt or hydraulic fluid using a clean cloth.

When working with Skydrol, refer to the Hydraulic Technical Precautions AMM TASK 29-00-00-910-802. The task has great information such as safety precautions and cleaning tips. Technicians should take advantage of the information available when working on the hydraulic system.

Being familiar with the above information will reduce cost to operators and reduce the rate of No Fault Found (NFF) returns by keeping the serviceable unit on the aircraft.

Bombardier also encourages maintenance personnel to report any information on the leak area and leak rate on the Material Return Authorization form MRA to help Bombardier in root cause investigations with our vendor.