What happened
At 0120 CST, a Canadian North Inc. Boeing 737-217, registration C-GKCP, was performing a night flight from Fort MacKay, Alberta, to Saskatoon, Saskatchewan. While on final approach to Runway 15, the crew heard a high-pitched noise and felt vibrations coming from the right engine, followed by two popping sounds. Immediately after, the Pratt & Whitney JT8D 17A engine lost power.
The flight crew initiated emergency procedures and declared an emergency. The captain took control of the aircraft and adjusted the flaps to 15 degrees in accordance with standard operating procedures for single-engine landings. Although sparks and flames were visible from the rear of the engine, the cockpit fire detection system did not alert the crew, and the fire bottles remained unused. The aircraft landed safely on Runway 15 and came to a stop.
Upon stopping, airport rescue and fire fighting personnel discovered flames inside the engine exhaust. Fire suppressants were applied to the engine, and thermal imaging was used to monitor hot spots. All passengers and the crew successfully evacuated the aircraft via the forward air stairs with no injuries.
The investigation
Investigators examined the right engine and the nacelle area, finding that the engine fire was contained within the engine casing and had not breached the fire warning detection harness. A teardown of the engine at an overhaul facility revealed a fractured low-pressure turbine (LPT) shaft.
Technical analysis showed that the LPT shaft had experienced a ductile shear overload failure. The investigation also identified damage to the high-pressure compressor (HPC) sealing tube and the 4.5 bearing stack. The investigation determined that the engine had accumulated 44,548 hours and 25,513 cycles since new. Maintenance records indicated the aircraft had been maintained according to the operator's approved control system, and the crew met all necessary certification and rest requirements.
Findings
- Wear on the number 4.5 roller bearing reduced the radial constraint of the low-pressure turbine shaft, causing it to flex.
- The flexing shaft made contact with the high-pressure compressor sealing tube aft fitting, creating localized heat and wear that compromised the shaft's physical properties.
- The LPT shaft ultimately suffered a ductile fracture, leading to the loss of engine power.
- The failure of the shaft caused the turbine rotor to contact the turbine nozzles, producing sparks.
- Oil leaked into the exhaust nozzle due to the failure of the No. 6 scavenge pump, which ignited due to high temperatures, causing the engine fire.
Safety action
Following the occurrence, the operator implemented changes to its maintenance schedule, including the installation and daily inspection of temperature stickers on the number 4 bearing scavenge line. Additionally, a safety bulletin was issued regarding the monitoring of engine oil consumption and temperature decals.