What happened
On December 2, 2013, during a periodic maintenance inspection at the GTL-LOT technical base at Warsaw Chopin Airport (EPWA), technicians were performing operational checks on the left and right main landing gear door actuator cylinders. The inspection was being conducted in accordance with specific maintenance tasks related to Airworthiness Directive 2011-0069R1.
During the procedure, it was observed that the main landing gear door covers had partially opened and failed to reach the fully closed position. While the covers could be moved manually and appeared to operate normally after being pulled by hand, the movement was accompanied by a distinct metallic sound. Due to this anomaly, the operational test was immediately suspended.
The investigation
The investigation involved the Polish State Commission on Aircraft Accident Investigation (PKBWL), LOT-AMS, and the aircraft operator. Following the discovery, the operator's Maintenance Control Center (MCC) was notified, and an internal report was generated. The operator subsequently contacted AIRTAC, the representative of the Type Certificate holder.
As part of the technical follow-up, AIRTAC requested a sample of hydraulic fluid from the "green" hydraulic system to perform necessary laboratory testing. Additionally, during the investigation process, a discrepancy was identified in the maintenance documentation. Specifically, an error was found in the service data regarding the installation of bushings (AMM 32-31-35-400-001-A) related to the assembly of the main landing gear door actuator cylinder. AIRTAC confirmed that this error existed in the provided maintenance manual revision.