What happened
On 9 September 2019, a Bombardier DHC-8-402, registration SP-EQG, operated by LOT Polish Airlines, was performing a flight from Warsaw (EPWA) to Poznań (EPPO). Approximately eight minutes after reaching a cruising altitude of FL180, the number two engine began to malfunction. The torque value dropped to zero, fuel flow increased sharply, and interstage turbine temperature readings fluctued erratically.
The asymmetrical thrust caused the aircraft to roll approximately 6 degrees to the right, prompting the pilot to disengage the autopilot and assume manual control. Shortly thereafter, a master warning for a fire detection was triggered. Passengers and cabin crew observed visible flames and burn marks on the engine nacelle, accompanied by loud bangs.
The flight crew immediately initiated the required memory items for an engine failure and fire. After extinguishing the fire using a single fire extinguisher bottle, the crew declared a MAYDAY and requested an emergency landing at Poznań (EPPO). To ensure safety, the captain prepared the cabin for evacuation. The aircraft landed uneventfully on runway 10 at 12:48 UTC. Following the landing, the crew executed an evacuation of the 73 occupants via the left-hand door without further incident.
The investigation
The PKBWL investigation examined the engine's condition through disassembly and testing conducted by Pratt & Whitney Canada. The investigation focused on the mechanical failure of the engine components and the subsequent fire. Investigators also reviewed flight data, maintenance records, and the crew's response to the emergency.
Findings
- The engine fire was triggered by a broken oil pipe supplying bearings #6 and #6.5. This leak allowed oil to escape into a high-temperature area (approximately 840°C) between the low-pressure turbine and the power turbine, resulting in a flame.
- The primary cause of the incident was fatigue damage to the no. 8 roller bearing, characterized by advanced spalling on the roller surfaces and cracks across the bearing raceway.
- The degradation of this bearing caused unstable motions in the engine's coupling, leading to the breakage of the front and rear shafts and the eventual interruption of torque transmission, which stopped the engine.
- All other engine damage, including damage to the turbine blades and stators, was determined to be secondary to the initial bearing failure and subsequent fire.