Aileron cable routing following adjustment
Effectivity: Challenger 300 and Challenger 350 aircraft
ATA 27-10 (aileron system)
This article aims to inform maintenance personnel about reported cases where damage was found on the aileron pulley support bracket located on the wing rear spar, near the aileron control surface. In one case, an unusual sound was reported when moving the ailerons during pre-flight.
The investigation concluded that the reported damage was due to the incorrect routing of the wing aileron cables. It is suspected that the reported condition was initiated during the latest maintenance event, most likely a 96- or 192-month inspection, during which the main landing gear (MLG) was removed and reinstalled.
Removal of the MLG per Aircraft Maintenance Manual (AMM) requires the removal of the tension from the wing aileron cables to allow the removal of the inboard aileron pulley assembly and, subsequently, the MLG pintle pin assembly.
It is suspected that, when the tension is removed from the wing aileron cables, the upper cable can drop below the aileron pulley bracket. When tension is reapplied to the wing aileron cables, the upper cable can press firmly against the pulley bracket, which prevents the cable from returning to its intended position. If not caught during the cable routing inspection and left in this condition, cycling of the aileron system during aircraft operation could result in damage to the aileron wing cable and/or aileron pulley bracket due to friction.
Pictures showing cable caught under pulley bracket (LH) and damage location (RH)
Maintenance personnel should be aware of the importance of proper cable routing and clearances when performing maintenance on cable systems. In addition to the cable tension requirements and the locking device installation, special attention should be taken to validate proper routing and clearances of the entire cable system before and after tension is applied. Cable tensioning and clearance guidelines can be found in AMM task 27-00-00-820-801 (General Rigging Instructions).
Pictures showing correctly routed cable
As a mitigating action, additional steps, notes and figures will be added to the AMM to make sure that proper access is given to allow thorough inspection at this specific location of the aileron cable circuit.
Bombardier strongly recommends that operators and maintenance service providers familiarize themselves with this possible condition and take the proper precautions through their quality control processes to avoid similar occurrences.