Accident Details
On a visual flight rules cargo flight from Bronson Creek, British Columbia, to Wrangell, Alaska, a DC-4 aircraft (serial number 10389) carrying three crew and approximately 16,600 pounds of cargo experienced an in-flight emergency. After an uneventful departure, as the aircraft reached about 1,500 feet above sea level, the crew heard a whining noise in their headsets. Switching inverters did not resolve the issue. Cockpit electrical instruments became erratic, and the number 2 engine on the left wing began to misfire. Its fire warning light illuminated briefly without the accompanying bell. The captain visually confirmed a fire on the number 2 engine, and the crew executed the engine fire drill, but the fire persisted.
The captain initiated a right-hand turn to return to Bronson Creek and announced that the number 2 engine had separated from the wing. Maximum power was applied to the remaining three engines, but the aircraft began to lose altitude. Both pilots held the rudder and aileron controls at full right deflection to counteract yaw and roll to the left. The aircraft shook violently, and the crew could not read any instruments. At about 50 feet above ground level, just short of the Iskut River, the throttles were closed. The aircraft descended rapidly; the burning left wing struck a tree as the fuselage contacted the river surface.
The three occupants escaped the burning aircraft. The first officer and load master swam to safety, while the captain is missing and presumed drowned. The aircraft was destroyed.
Investigation
The accident site is located in the Iskut River at 56°41.57 North, 131°06.22 West, 1.2 nautical miles from the Bronson Creek airstrip. Rescuers arrived by helicopter within 10 minutes and located the first officer and load master on the south shore. A search for the captain, involving three helicopters and three vessels, continued for two additional days but did not find him.
The number 2 engine and its propeller were found about 2.3 nautical miles from the crash site and recovered for examination. Sections of the firewall and engine mounts were sent to the Transportation Safety Board (TSB) Engineering Branch. Portions of the burned left wing and the number 1 engine were later recovered, but strong river currents and fluctuating water levels prevented further recovery.
Findings
The flight crew was licensed and qualified per existing regulations. The captain had approximately 12,500 total flying hours, including 1,500 hours on the DC-4; the first officer had about 2,900 total hours, including 420 hours on type. The crew had been on duty for about five hours, and the flight was their third of the day.
The 51-year-old aircraft had accumulated 50,754.8 total airframe hours and was maintained in accordance with regulations. Four days before the accident, the carburetor and fuel pump on the number 2 engine had been replaced. At takeoff, the aircraft weight (approximately 61,900 pounds) and center of gravity were within limits.
Examination of the recovered number 2 engine, a Pratt & Whitney R2000-7M2 (serial number P-108882) with a Hamilton Standard propeller, revealed that the engine and firewall separated from the wing due to failure of aluminum support channels. The inboard channels showed heat damage consistent with high temperatures, while outboard channels showed mechanical stress. The fire was localized in the engine compartment between the firewall and the accessory section, with the greatest heat concentration adjacent to the engine mounting structure. Potential fuel sources included pressurized fuel and hydraulic lines; potential ignition sources included electrical components, but the actual ignition source could not be identified.
The engine's physical separation likely affected the controls of the number 1 engine, as control cables for both left-wing engines shared common pulley brackets. With maximum power applied to the remaining engines, the aircraft could not maintain altitude or directional control because its speed fell below the minimum control speed (VMCA) for that configuration, which was unknown for an engine-separation scenario.
Probable Cause
The number 2 engine separated from the aircraft as a result of an intense fire in the wing. The loss of the engine rendered the aircraft uncontrollable, and the pilots were forced to land in the river.