Technical information

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When hydraulic fluid vents from the nose overboard drain mast, it is time to take action. Skydrol fluid is a
fire-resistant, phosphate ester-based fluid that works well as a hydraulic fluid, but also acts like a solvent caus-
ing damaged paint on belly panels.
Operators are reminded that when an emergency brake system operational check is performed it is important to
ensure the emergency brake lines are first flushed with alcohol and then blown out with clean, dry compressed
air. Refer to Chapter 32, Emergency Brake System Components – Maintenance Practices in the Model 560XL
Maintenance Manual.
If the hydraulic fluid continues to vent, the next likely cause to look for is internal leaks from the shuttle valves.
Citation Excel, XLS/XLS+ series aircraft have shuttle valves for the emergency main landing gear (MLG) brake
and landing gear extension systems. There are two shuttle valves installed in the emergency braking system, and
three shuttle valves installed in the emergency gear extension system.
To look for shuttle valve leaks, use the following procedures:
1. Brake Shuttle Valves
a. Position a bucket or absorbent material near the left MLG brake shuttle valve on the main landing gear.
b. Disconnect the pneumatic line from the brake shuttle valve. Refer to Chapter 20, Tubing, Hose and Fit
tings – Maintenance Practices in the maintenance manual.
c. Inspect for residual hydraulic fluid coming from the removed line.
Note: If residual hydraulic fluid is discovered, the shuttle valve needs to be reset by pumping the brakes firmly
or replacing the shuttle valve.
d. Connect the pneumatic line to the brake shuttle valve. Refer to Chapter 20, Tubing, Hose and Fittings
Maintenance Practices in the maintenance manual.
e. Repeat the above procedures for the right MLG brake shuttle valve.
2. Landing Gear Shuttle Valves
a. Gain access to the landing gear shuttle valves. Refer to Chapter 32, Landing Gear Auxiliary/Emergency
Control Systems - Maintenance Practices in the maintenance manual.
b. Disconnect the pneumatic lines from the landing gear shuttle valves. Refer to Chapter 20, Tubing, Hose
and Fittings – Maintenance Practices in the maintenance manual.
c. Inspect the lines for residual hydraulic fluid.
d. If residual fluid is found, lift the airplane on jacks. Refer to Chapter 7, Lifting – Maintenance Practices
in the maintenance manual.
e. Attach a hose to the pneumatic side of each landing gear shuttle valve and extend the hoses into buck
ets placed below the airplane.
f. Apply external electric and hydraulic power to the airplane.
g. Operate the retraction and extension of the landing gear several cycles. Refer to Chapter 32, Main
Landing Gear Hydraulic Systems – Adjustment/Test.
h. Inspect for hydraulic fluid leaking through the landing gear shuttle valves.
Note: If a hydraulic fluid leak is discovered, the shuttle valve(s) needs to be replaced.
Take Action When Hydraulic
Fluid Vents
PLEASE SEE NEXT PAGE
560XL, ATA: 29-20