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Learjet 45: MLG Actuators Bypassing Fluid

September 2010
Learjet 45 stretched main piston GT ring's backup rings

A Learjet 45 main piston GT ring's backup rings stretched and were lying over the seal causing fluid to pass.

Duncan Aviation recently repaired several Lear 45 MLG actuators for a customer who suspected they were bypassing fluid due to poor performance on the aircraft.

During teardown inspections, it was found the main piston GT ring’s backup rings had been stretched and were lying over the seal causing fluid to bypass. Visual inspection also found that the non-metallic scraper ring had allowed particulate contamination past and was causing wear and corrosion of the housing cap internal lands. 

You may have an actuator that is bypassing if you notice slow retraction and chunks of rubber missing from the MLG wheel due to contact with the door as its retracting. This damage is caused by the gear not retracting far enough when the door closes.

Duncan Aviation is in contact with Learjet about possible improvements for the scraper ring and piston seals. 


Jerry Cable
Cable, Jerry - Accessory Tech Rep - Lincoln, NE (LNK). Aviation professional since 1991.

Airframes: Astra, Challenger, Citation, Embraer, Falcon, Gulfstream, Hawker, Learjet, King Air, Global, Westwind

Hydraulic equipment and pumps, Pneumatic valves, Wheel and Brake, Emergency Power Supplies, Electric Motors, Mechanical Actuators, Landing Gear and Accessory Components and Systems Specialist.

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