What happened
At 15:02 MST, a Northwestern Air Lease Limited Jetstream 3212, registration C-FNAE, veered off the end of Runway 29 at Fort Smith, Northwest Territories. The aircraft, operating flight PLR 599, was arriving from Edmonton, Alberta, under instrument flight rules. During the landing, the aircraft drifted 60 feet left of the runway centerline and came to a stop 3ered 367 feet beyond the runway threshold in an area covered by approximately 18 inches of snow. There were no injuries among the 16 passengers and 2 pilots, though the number two propeller sustained damage.
Weather conditions at the time involved light snow, mist, and freezing fog, with visibility significantly reduced. While the crew was familiar with the airport, the runway surface had recently undergone maintenance. Sweeping operations had removed snow and sand, leaving a thin, polished layer of moisture on the pavement.
The investigation
The investigation focused on the runway surface condition and the flight crew's approach profile. Investigators found that runway maintenance had completed sweeping operations shortly before the arrival, but there was insufficient time to re-apply sand or conduct a new friction test. Consequently, the crew was unaware that the Canadian runway friction index (CRFI) had dropped significantly. A subsequent inspection after the accident revealed a CRFI of 0.18 in parts of the runway.
Technical analysis of the flight revealed that the aircraft was above the optimal glide path during the final approach. In an attempt to correct the descent, the pilot allowed the airspeed to increase to at least 20 knots above the reference speed. Furthermore, the application of full braking and reverse thrust was delayed, as the crew relied on aerodynamic drag to slow the aircraft from 120 knots to 90 knots before engaging the brakes.
Findings
- The descent profile during the final approach was too high for a touchdown in the intended zone.
- The aircraft's airspeed at touchdown was significantly higher than recommended, which, combined with a light tailwind, resulted in an insufficient stopping distance.
- The primary cause was the extremely low coefficient of friction on the runway surface, which had not been measured or reported to the crew following sweeping operations.
- The delay in applying maximum wheel braking and reverse thrust consumed vital runway length.
- Had the crew consulted CRFI charts prior to the approach, they likely would have recognized the need to reject the landing due to the high approach speed and altitude.