Landing gear side stay actuator leaks

Effectivity: Challenger 604/605/650 aircraft 

ATA: 32

By: Victor Silva (CSE) 

Bombardier Technical Services would like to inform operators and maintenance personnel on the topic of the main landing gear (MLG) Side Stay hydraulic fluid leaks and the mitigating actions that can be applied. 

The MLG side stay leaks have been voiced as a concern for certain operators, especially on the PN 19010-105 and previous assemblies.  We would like to highlight that there have been improvements introduced to this side stay assembly which have been introduced into the PN 19010-107 assembly.  

To better clarify, the side stay assembly PN 19010-107 has introduced a tandem seal (Variseal) and an upgraded rod bearing which prevents hydraulic fluid leakage between the piston and the cylinder assy. The side stay assy PN 19010-105 and pre had only a single seal at this location. Since the Variseal implementation on the -107, the reports of side stay hydraulic fluid leaks, beyond limits, from the cylinder to piston interface has greatly reduced and reliability data is showing a very positive improvement trend.   

Operators are encouraged to request that their pre-19010-107 side stay assemblies be upgraded when their units are sent to the OEM MRO shops, whether for inspection intervals or failures. Keeping in mind that there may be additional costs for this upgrade.  

Additionally, we would like to point out that side stay assembly hydraulic fluid leaks may occur soon after the side stay has been repaired or overhauled with new seals.  This is primarily due to the rod bearing seal surfaces being new and not having yet properly mated to the piston chrome micro-grooves.  

Therefore, as long as the observed hydraulic fluid seepage is within AMM hydraulic leak limits found in ATA 29, it is considered normal to notice some sweating or slight seepage on this interface for the first few gear cycles, which should reduce as the gear cycles increase.