What happened
On September 6, 2015, during the engine start-up sequence at EPBY airport, an EC 135 P2+ helicopter triggered a YAW SAS (yaw stability augmentation system) warning on the cockpit display. After completing the start-up cycle and activating the avionics, the pilot performed an autopilot test, which resulted in the recurrence of the YAW SAS warning alongside a GYRO warning, indicating a failure in the rate gyro sensor or gyroscope.
In an attempt to troubleshoot the system, the pilot deactivated all active SAS modes via the cyclic button and subsequently reactivated them. However, the GYRO warning persisted on the display. Following the procedure, the pilot shut down the helicopter and reported the malfunction to the Technical Coordination Center (CKT) duty engineer. An analysis confirmed a failure or lack of power to the YAW FOG fiber optic gyroscope within the yaw stability augmentation system.
Under the applicable Minimum Equipment List (MEL) category C, the aircraft was permitted to continue operations with a restriction to VFR-only flights. On September 12, 2015, the helicopter was relocated to SOT Warszawa-Babice. Technical personnel replaced the faulty gyroscope (S/N 00/00481) with a functional unit (S/N 00/03837). Following successful autopilot checks and a flight test on September 14, 2015, the MEL restriction was lifted, and the aircraft returned to unrestricted service.