Incident Overview
A flight conducted under visual flight rules experienced a dual engine power loss approximately 40 minutes after departure, resulting in a forced landing in a marshy wooded area 20 nautical miles southwest of Armstrong, Ontario. The aircraft was substantially damaged.
Flight Details
The aircraft departed from Dryden, Ontario, en route to Geraldton, Ontario, cruising at 5,500 feet above sea level with ambient temperatures aloft of -33°C. The flight was operating under visual flight rules.
Sequence of Events
About 40 minutes into the flight, the crew observed an abnormal right engine fuel flow indication. While troubleshooting, the right engine's rpm and fuel flow began to decrease, prompting a diversion toward Armstrong, Ontario. Shortly thereafter, the left engine's rpm and fuel flow also decreased, and the crew could no longer maintain level flight. At 0917 central standard time, the crew executed a forced landing into a marshy wooded area.
Injuries and Damage
The captain sustained serious injuries. The co-pilot and a passenger sustained minor injuries. All occupants were stabilized and transported to Thunder Bay, Ontario, for medical assistance. The aircraft sustained substantial damage.
Probable Cause
The official investigation identified two causes and contributing factors: 1) Suspended water in the fuel system precipitated out of solution and froze in the fuel distributor valve, blocking the fuel supply to the fuel nozzles and leading to loss of engine power. 2) The aircraft was being operated without a fuel additive icing inhibitor; use of such an additive would have inhibited ice formation and likely prevented the blockage. Additionally, two risk factors were noted: the fuel distributor valve on the Aero Commander 500B is exposed to outside air cooling, which under extreme cold can freeze super-cooled water droplets in the fuel stream, and the operator lacked procedures for using fuel additive icing inhibitor during winter operations.