What happened
A Cargojet Airways Limited Boeing 727-260, registration C-GUJC, was conducting a night cargo flight from Montréal International (Mirabel) Airport to Hamilton, Ontario, under instrument meteorological conditions. During a non-precision approach to Runway 30, the aircraft descended below the minimum descent altitude (MDA).
As the aircraft descended through approximately 865 feet, the enhanced ground proximity warning system (EGPWS) issued a "Too Low Terrain" caution. The crew attempted to level off at 800 feet, but shortly after, a "Pull up" warning triggered. In response, the crew initiated a go-around with significant nose-up pitch and thrust application. During this maneuver, the aircraft struck trees approximately 2.7 nautical miles from the runway threshold at an altitude of roughly 768 feet.
Following the strike, the crew performed a second approach to the same runway and landed successfully. A post-flight inspection revealed substantial damage to the right wing, the right landing gear door, and the anti-skid electrical harness. There were no injuries to the three crew members on board.
The investigation
The investigation examined the aircraft's descent profile, the functionality of the cockpit instruments, and the crew's adherence to company procedures. Investigators reviewed the flight data recorder (FDR) and cockpit voice recorder (CVR), though much of the relevant conversation had been overwritten due to the limited recording capacity of the CVR.
The investigation focused on why the aircraft descended below the MDA. While the altimeters and barometric settings were functioning correctly, the investigation explored whether the crew had misread the instruments or incorrectly set the altitude bugs. Additionally, the investigation looked into the crew's awareness of the EGPWS capabilities, specifically how the system behaved following the deactivation of the radio altimeter earlier in the flight.
Findings
- An incorrect altimeter bug setting that went undetected likely caused the aircraft to descend below the MDA.
- The crew was unaware of how the EGPWS functioned when the radio altimeter was inoperative, and the resulting "RFCF" caution alert caused confusion, delaying an appropriate terrain avoidance response.
- The decision to execute a go-around, rather than a more aggressive terrain avoidance maneuver, led to the aircraft striking the trees.
- The use of step-down techniques on non-precision approaches by large aircraft increases the risk of controlled flight into terrain.
Safety action
Cargojet Airways Limited implemented several corrective measures, including:
- Revising company policy to require the stabilized constant descent angle (SCDA) method for all non-precision approaches.
- Updating the Boeing 727 checklist to include a mandatory confirmation of MDA/DA/DH.
- Implementing stricter requirements for the independent setting and cross-checking of airspeed and altitude bugs.
- Enhancing training for flight crews regarding the reporting of aircraft defects and the procedures for pulling circuit breakers.