What happened
On 18 September 2013, an ATR 72-212A, registration PK-WFV, operated by Wings Abadi Airlines, was performing a scheduled passenger flight from Kendari to Makassar. The flight was carrying 70 passengers and 4 crew members.
While descending through approximately 6,000 feet, the aircraft began experiencing heavy vibrations. Simultaneously, the crew received alerts for the Propeller Electronic Control (PEC) 2 and the Alternating Current Wild Generator (ACW GEN) 2. The pilot in command declared a "mayday" to air traffic control, notifying them of engine problems. During the descent, the crew attempted to stabilize the aircraft by adjusting the condition levers, but the intense vibration persisted.
The aircraft landed safely at Sultan Hasanuddin International Airport. During taxiing, a nacelle overheat warning for the right engine activated, prompting the crew to shut down that engine. Upon inspection after parking, the crew discovered that the propeller blades were in inconsistent positions, with some feathered and others in reverse. Subsequent maintenance inspection revealed a broken trunnion pin and a deformed forward yoke.
The investigation
Investigators examined the aircraft's flight data recorder, cockpit voice recorder, and the physical condition of the engine and propeller assembly. The investigation focused on the mechanical state of the propeller blades and the internal components of the propeller hub.
Technical analysis included a Scanning Electron Microscope (SEM) examination of the broken components and a review of the propeller blade angle change mechanism. The investigation also looked into the relationship between the propeller's mechanical movement and the resulting vibration levels experienced by the airframe.