WestJet Encore flight 3532

A bang at 25,000 feet

WestJet Encore flight WEN3532 left Kamloops Airport in British Columbia at 15:12 Pacific Standard Time on 2 March 2023. Its destination was Calgary International Airport in Alberta. The Bombardier DHC-8-402, registered C-GVEN, carried 74 passengers, two pilots and two cabin crew members. The captain occupied the left seat and was the pilot flying. The first officer, in the right seat, was the pilot monitoring. The aircraft had two Pratt & Whitney Canada PW150A turboprop engines.

At 15:24:22, as the aircraft moved from climb toward cruise, the pilots heard a loud bang. They were at 25,000 feet above sea level, approximately 42 nautical miles north-northeast of Kelowna Airport. The autopilot disengaged. Torque from the right, No. 2 engine decreased while its inter-turbine temperature rose above the operating limits. The engine had suffered a fracture of a blade in the second stage of its low-pressure compressor. The damaged compressor caused an engine surge and a loss of power.

The full-authority digital engine control tried to recover the engine from the surge. The auto-ignition system activated, and the No. 2 engine fire warning illuminated. The control system increased fuel flow as it attempted to restore power. The engine could no longer burn most of the additional fuel. A fuel-rich mixture continued into the exhaust duct, where it burned and exposed the rear of the nacelle to intense heat. The fire detection system responded to that brief high heat exposure.

The DHC-8-402's compressor system has two independent compressors, each driven by its own turbine. The low-pressure compressor is an axial unit with three stages; the high-pressure compressor uses a centrifugal impeller. The three low-pressure rotors have integrated titanium-alloy blades. The engine control schedules fuel according to power-lever selection, measured torque and speed, sending an electrical signal to the fuel metering unit. The failure disrupted the compressor's airflow and power production while that control system attempted recovery. Investigators recovered both the cockpit voice recorder and flight data recorder and sent them to the TSB laboratory in Ottawa for analysis.

Shutdown and diversion

At 15:24:38, the pilots began the Engine Failure / Fire (FLT) / Shutdown checklist. They shut down the engine in 40 seconds. Completing the whole checklist took approximately two minutes because an air traffic control call interrupted the sequence. The pilots used the call to coordinate an amended clearance, declare an emergency and arrange a diversion to Kelowna. During the checklist, the captain told the first officer to take the time required and avoid rushing the items.

At 15:26:18, the pilots resumed the checklist. The captain confirmed that the right-engine fire warning had gone out and decided against discharging the engine fire extinguisher. He contacted the in-charge flight attendant and asked the cabin crew to look for visible signs of fire. They saw an oil streak along the inboard side of the nacelle but no visible fire. The flight crew completed the engine shutdown and continued the diversion with the remaining engine operating.

The aircraft made a single-engine approach and landed successfully on Kelowna's Runway 34. All 78 occupants survived, and there were no injuries. The TSB found that the pilots' actions, including securing the engine, complied with the flight manual, operating manual and company procedures. Its crew resource management analysis credited their prompt checklist response, coordination with air traffic control, use of the cabin crew's observations and methodical completion of the emergency procedure with the successful outcome.

Damage and the fractured blade

The right engine suffered substantial internal damage. Heat also damaged its cowlings, accessories and exhaust components. Investigators found discoloration on engine struts and fire shields, charring and deterioration of the exhaust P-seal, and damage around the rear of the nacelle. The fuel-to-oil heat exchanger had a fractured mounting pad. Vibration during the surge loosened all four mounting bolts and allowed the exchanger to move upward by approximately a quarter of an inch.

The damage survey required replacement of the aft upper cowling assembly, all aft nacelle cowling components and all exhaust components. Several panels and fairings showed discoloration, disbonding or delamination. The compressor blade fragment remained lodged in the second-stage compressor stator. Investigators assigned the fractured blade the reference number 1. Examination of the rotor also identified a crack in blade 15, in the same region near the blade root.

The rotor and recovered fragment went to Pratt & Whitney Canada's materials laboratory in Longueuil, Quebec, for examination under TSB supervision. Blade 1 had a fatigue crack starting beneath the pressure-side surface, approximately 0.0047 inches below it. The crack spread toward both edges and both surfaces of the blade before the final overload fracture. Investigators found no surface or metallurgical anomaly at the initiation location. Damage prevented them from determining the precise location of the crystallographic facet at the origin.

The examination of blade 15 revealed similar fatigue features and a matching initiation location. The changing rate of fatigue-crack growth indicated changing loading conditions, and the TSB considered it likely that the main crack developed over more than one flight. The engine had undergone restoration in Singapore in March 2022, when a new second-stage low-pressure compressor rotor was installed. At the occurrence, that rotor had completed 909 cycles against its 20,000-cycle life limit.

Resonance and bleed airflow

The investigation traced the fatigue to mechanical resonance around a low-pressure compressor speed of 26,000 rpm, within a band of 50 rpm either side. At that speed, repeating forces excite a natural vibration mode of the blade assembly and increase the vibratory stress. Engine data showed greater cumulative exposure to this speed band following restoration, mainly on flights between November 2022 and March 2023. The restoration had reduced compressor blade tip clearance, which remained within specification but allowed higher rotational speeds.

Pratt & Whitney Canada's analysis identified several conditions affecting blade stress. Temperatures below minus 25 degrees Celsius increased stresses associated with the resonance mode by a factor of 2.5. Chaotic or buffeting compressor airflow increased its excitation by approximately 10 percent. The TSB and manufacturer also examined flight recorder and engine monitoring data to assess the effect of bleed-air selection. Bleed air supplies functions including pressurization, cabin conditioning and airframe de-icing, and the crew can select minimum, normal or maximum flow.

Using the minimum bleed setting during climb and cruise increased low-pressure compressor speed and made exposure to the resonance band more likely, especially in cold ambient conditions. WestJet Encore's approved procedures had incorporated minimum bleed use for fuel economy; the manufacturer's operating manual described fuel savings of up to one percent. The TSB's risk finding was that minimum bleed could increase dwell time in the critical speed band and therefore likely increase the probability of cracks starting or growing in the existing rotor design. Exposure to that speed band was also possible with normal bleed selected.

The TSB's cause finding linked the failed blade to a high-cycle fatigue crack that began beneath the surface and propagated through mechanical resonance at 26,000 rpm. The flight data and metallurgical examinations connected the failed part's operating history with the stress mechanism. Both pilots held the appropriate licences and ratings. The aircraft had no recorded defects or deferred maintenance items, and the TSB found no indication that medical or physiological factors had impaired pilot performance.

The exhaust fire and safety changes

After the blade failed, the control system increased fuel flow from 1,432 to 1,538 pounds per hour in its recovery attempt. The rich exhaust mixture burned in the duct. Hot gases then backed into the aft nacelle through the gap between the exhaust duct and shroud, where cooling air normally flows outward. Soot in the gas path was consistent with incomplete combustion. Heat exposure was greatest near the exhaust nozzle shroud and diminished toward the front of the engine. Shutting down the engine stopped the fuel supply and the fire warning went out.

Pratt & Whitney Canada issued Special Instruction 72-2023 on 22 July 2023 for endoscopic fluorescent penetrant inspections of second-stage compressor blades, particularly near the hub on the pressure side. Any detected crack required removal of the engine before its next flight and replacement of the rotor at a restoration facility. A further instruction, issued on 30 January 2024, targeted engines with a higher statistical probability of blade distress and used engine monitoring data to track their operation. WestJet Encore incorporated both inspection instructions into its maintenance program; those additional inspections found two engines with fractured rotors.

WestJet Encore began a collaborative engine-data collection program in March 2024. On 15 May 2024, it revised its operating manual to require normal bleed through the top of climb until cruise power was set, with maximum flow available when desired. After cruise power was set, crews could select the flow required. Pratt & Whitney Canada's trend data confirmed that the revised procedures reduced compressor speed sufficiently to reduce exposure to the resonance band.

The manufacturers also changed the engine control response to significant engine events. Pratt & Whitney Canada issued Service Bulletin 35381 on 9 June 2025, introducing a modified fuel-flow limit schedule and a significant engine event detection function. Transport Canada's directive CF-2025-44, dated 12 September 2025, mandated the software upgrade with compliance due within 3,000 flight hours or 14 months from its effective date, whichever came first. The TSB Board authorized release of the completed investigation on 27 May 2026, and the final report was released on 22 September 2026.