What happened
On February 4, 2009, at approximately 16:34 local time, a UNI Airways Dash 8-300, registration B-15239, was performing a scheduled passenger flight from Magong Airport to Tainan Airport. The aircraft was carrying 50 passengers and 4 crew members.
During the takeoff roll on Runway 02, before reaching $V_1$ speed, the flight crew heard loud, abnormal banging noises. Simultaneously, the Interstage Turbine Temperature (ITT) rose to approximately 1069°C, and the cockpit instruments indicated an engine fire warning for the number one (left) engine. The air traffic controller also notified the crew that smoke and fire were visible from the left engine. The pilot responded by reducing power and bringing the aircraft to a stop on the runway.
Following the stop, the crew initiated emergency procedures and evacuated all passengers to a safe distance of 100 meters upwind. One passenger sustained a minor injury. All occupants were safely transported to the terminal via shuttle bus by 16:48.
The investigation
The investigation examined the damage to the number one engine and the failure of the first-stage power turbine rotor blades. Investigators analyzed engine teardown reports, maintenance records, and X-ray inspection results. The investigation also reviewed the effectiveness of existing service bulletins and inspection protocols provided by the engine manufacturer, Pratt & Whitney Canada.
Findings
- The primary cause of the engine fire was a manufacturing defect in the number one engine's first-stage power turbine rotor blades, specifically excessive shrinkage porosity.
- This porosity led to the formation of fatigue cracks, which eventually caused a blade to fracture during normal engine operation.
- The resulting imbalance caused the turbine rotor to vibrate violently, leading further damage to subsequent turbine stages and the engine casing.
- The breakage caused engine gases and oil to mix and ignite within the engine nacelle, triggering the fire warning.
- Existing X-ray inspection procedures used by the manufacturer were unable to reliably detect all blades containing such defects.
- A discrepancy was noted in maintenance records where a bearing seal hole was misaligned by 90 degrees relative to the overhaul manual specifications.