Incident Overview
On January 17, 2018, a Eurocopter EC 135 P3 helicopter (no registration provided) was undergoing a test flight after 12 months of hangar maintenance. The aircraft was based at EPSC Szczecin. The crew consisted of a professional helicopter pilot and a mechanic; both occupants sustained no injuries.
Sequence of Events
During the initial hover, the mechanic, seated in the passenger cabin, observed a red filter FAIL light illumination on the main electrical master box for the left generator bus (bus #1). The pilot checked the CAD and VEMD displays and saw no abnormal indications. Nevertheless, the pilot aborted the test flight and notified the SOT (Station Operations Team) in Szczecin.
Mechanics from SOT Szczecin performed a test in accordance with AMM 24-30-00, step 5-1. The test yielded a positive result, indicated by a green filter light. A decision was made to continue the test flight. After takeoff, the same red FAIL light reappeared. The test flight was terminated. Further tests were conducted but produced negative results.
Technical Investigation
The Technical Coordination Center contacted the manufacturer. Following consultation, a bit readout of the ARINC 429 data bus was performed on labels 37, 370, 371, and 372. Three errors were detected on label 37. Based on this finding, the manufacturer recommended replacement of the electrical master box #1 for the left generator.
After replacing the electrical master box and conducting successful tests, the helicopter was cleared for a control flight and subsequently returned to service.
Probable Cause
The incident resulted from a malfunction of the main electrical master box #1 for the left generator bus.
Safety Actions
The operator discussed the event with all operational personnel. No safety recommendations were issued by the Polish State Commission on Aircraft Accident Investigation (PKBWL).