History of the Flight
Bearskin flight 372, a Fairchild SA227-AC aircraft registered C-FFZN, was operating a regular scheduled domestic passenger flight from Sudbury, Ontario, to North Bay. The aircraft departed Sudbury at 1847 eastern standard time carrying two crew members and 16 passengers. The flight was conducted under instrument flight rules at an altitude of 9,000 feet above sea level.
The co-pilot, seated in the right seat, was at the controls. Upon arrival in the North Bay area, the flight was radar vectored for an instrument landing system straight-in approach to runway 08. The crew flew the approach at appropriate airspeeds for the weight and flight conditions.
Touchdown occurred at the runway threshold at or near the centerline at the correct airspeed and with the aircraft in the correct landing configuration. As the main landing gear wheels contacted the runway, the nose pitched down abruptly and the aircraft began to veer left. The co-pilot applied heavy right brake and reverse thrust on the right engine but could not prevent the aircraft from going off the left side of the runway into deep snow.
There were no injuries to the two crew members or the 16 passengers. Emergency evacuation was not required. Passengers exited through the normal cabin airstair door and were transported to the terminal by airport van.
The occurrence took place at North Bay Airport at 1915 EST during darkness.
Meteorological and Aerodrome Information
At the time of departure from Sudbury, weather was reported as a precipitation ceiling of 1,100 feet obscured, visibility three-quarters of a mile in light snow, wind from 050° at 23 knots, temperature -13°C, dew point -18°C.
At North Bay, the 1915 EST special weather observation reported a precipitation ceiling of 200 feet obscured, visibility one-quarter mile in moderate snow and blowing snow, wind from 080° at 19 knots gusting 25 knots.
Runway 08 at North Bay is oriented 076° magnetic, 10,000 feet long by 200 feet wide. The asphalt surface was plowed full width, 30% bare and dry, 70% snow drifts up to one inch deep. The runway condition report was broadcast to the flight crew during approach.
Aircraft Damage and Examination
The aircraft No. 1 engine and propeller were damaged. The four blades of the No. 1 propeller were bent and curled in the feathered position with no leading edge damage. The No. 2 engine and propeller were undamaged.
On the left dual main landing gear, both tires had flat spots worn through to the cords, with no other damage. Workers who recovered the aircraft reported that the left main wheels would not rotate until heat was applied from a portable heater. The right main landing gear tires were undamaged and in good condition with no evidence of binding or discrepancies.
A dual black scuff mark began approximately 2,300 feet from the runway threshold and 26 feet left of centerline, extending 664 feet before going off the left side of the runway. No other relevant marks were found.
Examination of the brake system revealed that snow entering the warm brake area can melt and then freeze in below-freezing temperatures, causing the brakes to bind. The aircraft was equipped with dual-rotor hydraulic-operated multi-disk wheel brakes with no means to prevent blowing snow from entering the brake disk area. The brakes were not power-assisted nor did they incorporate anti-skid.
Findings
The left main landing gear wheels did not rotate from touchdown until the aircraft went off the runway, as indicated by the rapid nose drop, continuous scuff mark, and flat-spotted tires. The left brake was frozen, preventing wheel rotation. Applying heat to the brake assembly allowed free rotation, confirming the brake was frozen.
The right brake appeared not to function during the landing roll; the reason was not determined. There was no evidence of right brake activation on the tires or runway.
Directional control of the aircraft was lost during the landing roll, leading to the runway excursion.