What happened
On October 15, 2021, an Embraer EMB 120 ER, registration HA-FAL, was operating a scheduled passenger flight from Pori (EFPO) to Helsinki-Vantaa (EFHK). The flight, operated by BASe Airlines, carried two pilots, one cabin crew member, and six passengers.
While climbing through flight level 170, the crew encountered light icing and turbulence, prompting them to request a descent to flight level 150. As the captain adjusted the power levers to reduce thrust for the descent, the engine monitoring instruments indicated a sudden drop in torque and fuel flow in the right engine. The fuel flow plummeted from 230 kg/h to 70 kg/h, and torque levels dropped to nearly zero. Despite attempts to increase power, the right engine failed to respond to lever movements.
Recognizing an engine malfunction, the crew performed memory items and declared a MAYDAY at 07:51. Following the Quick Reference Handbook (QRH) procedures, the crew shut down the malfunctioning right engine at 07:55. The aircraft continued the flight on a single engine and landed safely at Helsinki-Vantaa at 08:15 using an ILS approach on runway 15.
The investigation
The investigation examined the aircraft's digital flight data recorder (DFDR), radar data, and radio communications. A technical inspection by the airline's mechanic revealed that the power loss was caused by a failure in the P3 line of the right engine.
In the engine's Hydromechanical Metering Unit (HMU6), the fuel flow is regulated based on P3 pressure data and power lever position. The failure of the P3 line caused the HMU to regulate fuel flow to its minimum setting, effectively pinning the engine at near-idle power. This occurred without any prior warning from the cockpit alert systems. The mechanic repaired the fault, and the engine passed a test run.
Findings
- The primary cause of the power loss was a failure in the P3 line, which prevented the HMU from responding to power lever inputs.
- The crew successfully managed the emergency by following established procedures, shutting down the failed engine and operating the aircraft safely on one engine.
- The cockpit voice recorder (CVR) could not be utilized for the investigation because the recording was not properly secured following the incident, allowing the critical period of conversation to be overwritten by noise.