Edmonton, Alberta, 12 May 2021 — In its investigation report (A20W0016) released today, the Transportation Safety Board of Canada (TSB) found that a flap malfunction combined with the flight crew’s handling of the “flaps fail landing procedure” led to a loss of aircraft pitch control and subsequent contact of the rear fuselage with the runway while landing in Calgary, Alberta.
On 23 February 2020, a Bombardier Challenger 605 operated by the Canadian Pacific Railway Company (CP) departed Palm Beach International Airport, Florida, United States, for Calgary International Airport, Alberta, with three crew members and 10 passengers on board. During the descent, the flight crew attempted to deploy the flaps and immediately received a “FLAPS FAIL” caution message. The flight crew proceeded to complete the flap failure procedure from the Quick Reference Handbook (QRH).
The investigation found that after the nose wheel touched the ground during the landing, maximum reverse thrust was selected; however, insufficient pressure was applied to the control column to maintain the nose landing gear on the runway. As a result, the nose pitched up, and the rear fuselage contacted the runway. The aircraft’s stall protection system then commanded a rapid nose-down control input, leading to damage to the forward section of the aircraft when the nose wheel contacted the runway. Once the landing was completed, the aircraft continued to the intended parking area. There were no injuries to any of the aircraft occupants, although there was significant damage to the aircraft.
The flap failure occurred when one of the flap flexible drive shafts failed. Moisture entered the flap flexible drive shaft casing, likely through the undetected puncture holes and the drive shaft casing to flap actuator interface, which led to the subsequent corrosion and failure of the inner drive shaft. As the aircraft’s actual annual utilization was approximately half of that expected by the manufacturer, the calendar time interval between maintenance inspections increased. As a result, the corrosion that developed was not detected because the shaft had not yet reached the 2400 flight-hour maintenance interval.
The pilot monitoring did not read the cautions included on the flaps fail checklist out loud to the pilot flying during the completion of the QRH procedure. As a result, information critical to the safe operation of the aircraft was not brought to the pilot flying’s attention.
It was also found that the Challenger 605 flight simulator used for recurrent training did not accurately represent the zero-flap handling characteristics of the aircraft when the thrust reversers are deployed, nor was it required for certification. As a result, the flight crew was inadequately prepared to prevent, or recover from, the nose pitch-up that occurred when the thrust reversers were deployed.
Following the occurrence, CP amended its procedures to address the differences between the caution and warning notes published in the Aircraft Flight Manual and QRH. Bombardier issued a temporary revision to the QRH flap fail procedure. The TSB issued an Air Safety Information Letter (A20W0016-D1-L1) to highlight the Challenger 605 series flap system inspection interval, and a CL60 series cross-fleet product improvement observation.
See the investigation page for more information.
The TSB is an independent agency that investigates air, marine, pipeline, and rail transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.