Incident Overview
A multi-engine fire bomber, operating without a load of fire retardant, was en route to a fire base when it encountered forecast instrument meteorological conditions. The flight crew descended to lower altitudes to remain in visual flight rules (VFR) conditions beneath the cloud layer.
Sequence of Events
During the final minutes of the flight, the aircraft descended to less than 1,300 feet above ground level over nearly level terrain. As the aircraft approached rapidly rising terrain at the end of a broad open valley, it inadvertently entered instrument meteorological conditions (IMC). While maintaining a nearly wings-level attitude, the airplane impacted a ridge approximately 240 feet below its top.
Crew Actions
The First Officer, who was pilot flying, had asked the Captain about ten minutes before impact whether their altitude was sufficient to clear the upcoming terrain. The Captain did not respond, and the First Officer did not further challenge the Captain on the issue.
Witness Reports
Witnesses in the area reported low clouds with ceilings around 200 feet above ground level, visibility of one-quarter mile or less, and rain with fog. One witness briefly saw the airplane flying "very low," while others only heard the aircraft.
Probable Cause
The flight crew's failure to maintain terrain clearance during low altitude flight in low ceiling and visibility conditions. Contributing to the accident was the flight crew's failure to adequately monitor their location with respect to the rising terrain environment ahead, and their lack of crew resource management communication as a crew.