What happened
On October 10, 2017, at approximately 10:35 LMT, a student pilot was performing a landing maneuver at the Dęblin aerodrome (EPDE) following the completion of a training task. During the approach to the landing pad, the pilot observed the Engine Indicating System (EIS) power indicator changing from white, representing normal operation, to yellow, indicating a warning. This color change fluctuated between white and yellow at short intervals.
Immediately prior to touchdown, the power indications disappeared entirely, only to reappear intermittently. After the helicopter had landed and the engine was shut down, the power readings continued to fluctuate between 0% and 20%. Upon restarting the electrical power, a "throttle failure" message was displayed on the system.
The investigation
The investigation, conducted by the AOSL WSOSP Dęblin, focused on the electrical and mechanical components of the engine monitoring system. Maintenance personnel examined the engine instrumentation and identified a malfunction within the throttle position sensing mechanism. To rectify the issue, a new throttle position sensor (p/n: HG70-2308, s/n:120025) was installed along with the required kit as per SB14-031. Following the installation, the system was adjusted in accordance with the maintenance manual (MM 72-A10). Post-maintenance testing confirmed that the throttle position measurement system was functioning correctly.
Findings
- The primary cause of the erroneous engine power indications was the faulty operation of the throttle position sensor.
- The aircraft was subsequently returned to service after the replacement and calibration of the sensor.