Accident
On the day of the accident, a Douglas DC-3C aircraft, registered as C-FBZN and owned by Transfair, was destroyed shortly after takeoff from the La Grande-LG-4 airstrip in Quebec. Both crew members suffered fatal injuries. The aircraft departed at 06:35 for a visual flight rules (VFR) charter flight to Lac Bienville, Quebec, carrying drums of kerosene (Jet B) for a Hydro-Quebec contractor.
Pre-Takeoff Conditions
A system for de-icing the wings on the ground was available at the airport but was not used. Instead, a broom was used to remove snow and ice from the wings. The airplane took off with some ice still present on the wing surfaces.
Takeoff and Engine Failure
An eyewitness reported that the takeoff from runway 10 appeared normal. The pilot initiated a left turn at low altitude immediately after the landing gear was retracted. Shortly after takeoff, the crankshaft of the left engine failed between the two banks of cylinders. The rear section of the engine continued to operate because it remained connected to its key accessories, including the magnetos; however, its power could not be transmitted to the propeller. The tachometer, mounted on the rear section, continued to provide an engine rpm reading.
Consequences of Crankshaft Failure
The failure of the crankshaft caused the front part of the engine to misfire, with pistons no longer synchronized with the ignition timing of the magnetos. This seriously disrupted engine operation and led to a rapid decay of rpm in the front section, which drives the propeller governor. The propeller governor, which regulates propeller rpm by adjusting blade pitch angle, detected the decrease in engine power and adjusted the blades to a lower pitch angle to reduce torque required to maintain rpm. The resulting additional drag from the left propeller operating at low pitch was aggravated by the increased power needed to windmill the propeller, due to resistance from the erratic functioning of the engaged cylinder bank.
Crew Actions and Stall
The crew may not have recognized the engine failure and was unable to feather the left propeller in time. A left-hand turn was initiated in an attempt to return for a landing. While the pilot tried to maintain the aircraft in flight, its critical angle of attack was probably exceeded, and the aircraft stalled during the turn.
Probable Cause
The official probable cause stated that ice was present on the wings of the aircraft at takeoff. Following the failure of the left engine after takeoff, and while the pilot may have been attempting to return to land, the aircraft stalled in the turn and crashed.