Incident Overview
On 26 July 2017, the crew of an EC 135 P2+ helicopter operated by the Polish Medical Air Rescue (LPR) was dispatched on a mission to transport a patient from Częstków. During the flight, two minutes before landing, the Crew Alerting Display (CAD) showed a "WARNING AP Trim" message. The landing at the patient location was uneventful. The subsequent engine start and flight to a hospital in Sieradz proceeded without issues, and the autopilot functioned correctly.
In-Flight Autopilot Failure
After landing in Sieradz, the crew restarted the helicopter. The "WARNING AP Trim" message reappeared, accompanied by an audible tone in the headsets. This time, the autopilot could not be engaged. Following the checklist, the crew decided to return to their base in Łódź under VFR without autopilot. The landing at the base was normal.
Post-Flight Troubleshooting
After landing, the pilot attempted an autopilot test, but none of the buttons on the autopilot panel responded. The helicopter was temporarily grounded, and the event was reported to the Technical Coordination Center (CKT). The aircraft was released for operations under MEL 22 item 1 category C, allowing VFR flights without autopilot, effective until August 5, 2017.
Maintenance and Resolution
From July 28 to August 1, 2017, technical personnel at Warsaw Babice Maintenance Station performed diagnostics according to KOC No. 083/011/HXE/1/1. They checked the autopilot per Thales ASMM EC-135 F911, which returned a correct result, and verified voltages at connectors H and L, and the CADA and CAEA APM modules. The decision was made to replace the autopilot module APM 2000. The unit P/N 416-00297-007, S/N 168 was removed and replaced with S/N 1272 in accordance with AMM 22-10-00, 4-1. A test flight per MSM 05-65-00, 6-1 was conducted successfully. As of August 1, 2017, the MEL restriction was lifted, and the helicopter was fully serviceable.
Cause
The cause of the incident was a faulty electronic mode selection module of the autopilot block APM 2000.
Safety Recommendations
The Polish State Commission on Aircraft Accident Investigation (PKBWL) did not issue any safety recommendations.
Operator's Preventive Actions
The incident was discussed with all LPR operational personnel.