What happened
At 0632 Pacific standard time, a WestJet Airlines Boeing 737-200 departed Abbotsford International Airport, British Columbia, bound for Calgary, Alberta. The aircraft was carrying 52 passengers and 5 crew members. Shortly after climbing through 15 and 00 feet, the flight crew heard a series of loud bangs, which were characteristic of an engine compressor stall. Simultaneously, instruments for the No. 2 engine indicated a decline in power turbine speed and abnormally high exhaust gas temperature.
Passengers seated on the rear right side of the cabin reported seeing flames exiting the engine exhaust during the loud bangs. The pilot flying leveled the aircraft at approximately 3000 feet and executed the engine limit/surge/stall quick reference checklist. After confirming the issue with the No. 2 engine, the crew reduced thrust to idle, at which point the engine appeared to stabilize. The crew notified Abbotsford Tower of their intention to return to the airport. The aircraft landed safely on Runway 25 at 0718 with no injuries or fire reported on the ground.
The investigation
The investigation focused on the mechanical failure of the engine's inlet nose dome. Engineering analysis revealed that the threads on stud number one had been significantly damaged prior to being installed into the stud boss. This initial damage caused the thread in the stud boss to fail in shear. As the remaining material could no longer maintain the necessary clamping force, the load shifted disproportionately to studs two and four, eventually causing their threads to fail as well.
This loss of clamping force allowed the nose dome to lever stud number three out of the front accessory support, bending the stud and breaking the boss. The investigation determined that the compressor stalls were a direct result of this dislodged dome disrupting the airflow into the engine. While passengers saw flames, a teardown of the engine confirmed no internal fire occurred; the visible flames were likely caused by engine surges resulting from the distorted inlet airflow.
Findings
- The engine experienced multiple compressor stalls because the inlet nose dome assembly detached during flight.
- The detachment was caused by a critical loss of hold-down clamping force.
- The threads on stud number one were damaged before they were installed in the stud boss.
- The loss of the first stud caused a progressive failure of the remaining studs (two, three, and four) due to increased load.