A 1957 built de Havilland Canada DHC-3 Otter was operating a charter flight between Cochenour and Sandy Beach Lodge, both in Ontario Canada. Onboard the float-equipped aircraft, for the short 25 miles flight, was a pilot and 6 passengers. One of the passengers occupied the right-hand seat in the cockpit, with the remaining five in the cabin.
All that remained of the aircraft after the fire had died out (Source; baaa-acro.com © Unknown)
The take-off and climb to cruise phase of the flight were uneventful. Shortly after the pilot levelled off the aircraft for the short cruise, at ~2500 feet, the pilot heard a popping sound and a slight loss of engine power. Smoke started to appear in the cabin at the same time. A scan of the engine instruments revealed no abnormal indications and there was no fire warning.
Suspecting a cylinder on the engine had failed the pilot initiated a return to Cochenour. At that time the passenger in the righthand cockpit seat alerted the pilot to flames near the floor at the front right-hand side of the cabin. The pilot then multitasked, Flight Services was informed of the emergency, told the passenger to evacuate the cockpit and attempted to extinguish the fire using the hand-held fire extinguisher on the flightdeck.
The aircraft in better days.... (Source; baaa-acro.com © Unknown)
The smoke intensity rapidly increased and thick black smoke filled the cabin, reducing visibility and causing respiratory problems for all onboard the aircraft. To enable forward vision, the pilot opened the left crew door and initiated an emergency landing on McNeely Bay the nearest possible landing site while the aircraft was on fire., The emergency landing, although hard, was successful and the aircraft remained upright and afloat. Using the main door all occupants evacuated the aircraft and were picked up by boats that were out on McNeely Bay. The pilot suffered second-degree burns to his face and right arm, while the passenger that had been in the cockpit sustained burns to his right leg. The other passengers escaped serious injuries. The aircraft burned down within minutes of the emergency landing.
The accident was investigated by the Transportation Safety Board of Canada (TSB) They concluded that the accident was caused by the failure of the exhaust valve in the number 2 cylinder of the Pratt & Whitney R140-61 radial engine. This caused flaming cases to enter the exhaust manifold causing overheating of the cylinder head and the exhaust manifold. The failed cylinder head allowed hot gases to escape causing overheating of materials, ultimately resulting in smoke and fire in the cockpit and cabin. In their report (available by clicking here) the TSB concluded that the cause of the accident was;
"Continued operation of the engine following an exhaust valve failure on the No. 2 cylinder resulted in a flaming gas path near the right side of the firewall, an exhaust system overheat, and a subsequent cabin fire"