What happened
On April 22, 2004, a Raytheon B300 (registration C-GEJE), operated by Grant Executive Jets Inc., was performing a repositioning flight from Earlton to Timmins, Ontario. While conducting an instrument landing system (ILS) approach to Runway 03, the aircraft encountered moderate icing conditions.
As the aircraft descended, the crew observed ice accumulating on the engine nacelles and parts of the wing not covered by de-icing boots. During the approach, the aircraft was flying in level flight at 2700 feet above sea level. The autopilot was engaged in altitude-hold mode but was not set to approach mode, meaning the aircraft was not following the glide slope.
As the pilot flying reduced engine power, the airspeed dropped from approximately 135 KIAS to 98 KIAS. The aircraft then stalled without any prior warning from the onboard systems. The pilot flying immediately initiated recovery by applying maximum power and lowering the nose. The aircraft lost approximately 850 feet during the event, reaching a minimum altitude of 800 feet above ground level. Following the recovery, the crew executed a missed approach and subsequently landed the aircraft safely on a second attempt.
The investigation
The TSB examined the aircraft's flight data recorder, which revealed that the power reduction led to a rapid decay in airspeed. The investigation also looked into the aircraft's ice protection systems, finding that while the de-icing boots were functioning correctly, they were not preventing all ice accumulation.
Investigators reviewed the flight crew's training records, noting that while both pilots were qualified, they had not undergone recent, formal Crew Resource Management (CRM) training. The investigation also analyzed the aircraft's stall warning system, which uses a lift transducer vane. It was determined that this system was not designed to account for the aerodynamic changes caused by ice accumulation on the wing surfaces.
Findings
- The aircraft stalled because the flight crew failed to monitor the airspeed as it decreased during the approach.
- Ice accumulation on critical surfaces increased the stall speed above normal parameters.
- The stall warning system failed to activate because it could not compensate for the reduced stall angle of attack caused by ice.
- The autopilot was not transitioned to approach mode, preventing the aircraft from capturing the glide path and leading to a loss of altitude during power reduction.
- The crew did not adhere to the aircraft flight manual's requirement to maintain a minimum airspeed of 140 KIAS during sustained icing conditions.
- Ineffective crew resource management resulted in a lack of monitoring of critical flight parameters and a failure to discuss icing procedures during the approach.