What happened
On a flight testing mission near Abbotsford International Airport, a Bombardier DHC8-402 (registration C-FBAM) experienced an uncommanded shutdown of its number one engine. The aircraft, which was undergoing certification testing for an air tanker conversion, was operating in uncontrolled airspace approximately 15 nm north of Abbotsford. During a level turn at 4,500 feet, the engine failed without warning. The crew successfully utilized the alternate feather system to stabilize the propeller and returned the aircraft to Abbotsford safely. There were no fatalities or injuries during the event.
The investigation
Investigators examined the PW150A engine and reviewed maintenance history. The engine had experienced significant periods of inactivity, including time spent in storage and undergoing conversion work. While the engine logs showed compliance with certain storage inspections, investigators looked into the engine's recent service history at repair facilities. The investigation also involved a teardown of the engine by both the TSB and Pratt & Whitney Canada.
Technical analysis focused on the accessory gearbox (AGB) and the tower shaft. Investigators found that the engine's chip detector had recorded a fault regarding metal in the oil approximately two hours before the shutdown, though this information was not accessible to the pilots during flight. Additionally, the investigation noted that the cockpit voice recorder data was lost because the device was overwritten when external power was connected to the aircraft after the landing.
Findings
- The in-flight shutdown was caused by fuel starvation resulting from a loss of drive to the accessory gearbox.
- The failure originated from the disintegration of the No. 30 thrust bearing.
- Corrosion and pitting on the bearing components were likely caused by the ingress of contaminants, potentially introduced via a leaking roof while the engine was undergoing repairs in a shop.
- The failure of the No. 30 bearing allowed the tower shaft to shift longitudinally, causing it to disengage from the spiral bevel gear on the high-pressure compressor shaft.
- Maintenance procedures during the engine's repair period were insufficient to prevent or detect the introduction of the contaminant.
- The flight crew had no prior warning of the impending failure because the engine monitoring system's chip detector fault was not available to them in the cockpit.