What happened
On June 27, 2011, a Bombardier DHC-8-314, registered JA805K, operated by ANA WINGS CO., LTD., departed from Osaka International Airport as a scheduled flight. While climbing through 6,700 feet, the flight crew heard a loud noise originating from the No. 1 engine. This was accompanied by a loss of engine power and an inter-turbine temperature (ITT) that exceeded the 950 ºC limit.
In response to the engine malfunction, the crew shut down the No. 1 engine and initiated a return to the airport. After declaring an emergency and receiving priority from air traffic control, the aircraft landed safely at Osaka International Airport at 17:18. There were 34 people on board, including 30 passengers and four crewmembers, and no injuries were reported.
The investigation
The Japan Transport Safety Board (JTSB) conducted a teardown and fracture surface inspection of the engine at the manufacturer's facility, with assistance from the Transportation Safety Board of Canada. The investigation focused on the internal state of the Pratt & Whitney Canada PW123B engine to identify the source of the mechanical failure.
Inspectors examined the combustion chamber, high-pressure turbine (HPT), low-pressure turbine (LPT), and power turbine (PT) sections. The investigation also reviewed the aircraft's maintenance history, airworthiness certificates, and meteorological conditions at the time of the incident.
Findings
The inspection revealed extensive internal damage throughout the engine's turbine stages. Specifically, a section of the cooling ring attached to the combustion chamber outer liner had broken away due to the progression of fatigue cracks. This missing fragment, measuring approximately 63 x 13 mm, was carried downstream by combustion gases.
As this piece traveled through the engine, it struck the high-pressure turbine blades, causing all 38 HPT blades to fracture. The resulting debris continued through the engine, causing mechanical degradation to the LPT blades and the total fracture of all blades in the power turbine (PT) stages. The investigation concluded that the fatigue crack progression in the cooling ring was the primary driver of the downstream destruction of the turbine components.