What happened
While operating as part of an aerial firefighting effort, a multi-engine fire bomber was transiting to a fire base. The aircraft was not carrying any retardant at the time of the incident. During the cruise phase of the flight, the crew encountered weather conditions that had been forecast as instrument meteorological conditions (IMC). To maintain visual flight rules (VFR) and remain beneath the cloud layer, the crew performed several descents to lower altitudes.
As the flight progressed, the aircraft was operating at an altitude of less than 1,300 feet above ground level over relatively flat terrain. As the flight path approached a section of rapidly ascending terrain at the edge of a wide valley, the aircraft entered IMC. Shortly after entering these conditions, the aircraft struck a ridge approximately 240 feet below its peak while maintaining a nearly wings-level attitude. Local witnesses reported extremely poor visibility, with fog, rain, and cloud ceilings as low as 200 feet above the ground. Some observers noted the aircraft flying at a very low altitude shortly before the impact.
Findings
Investigation into the flight dynamics revealed that the First Officer was the pilot in command at the time of the crash. Approximately ten minutes before the impact, the First Officer had questioned the Captain regarding whether the current altitude was sufficient to clear the approaching terrain. The Captain did not provide a response to this inquiry, and the First Officer did not further contest the altitude setting. The unintentional entry into instrument meteorological conditions while flying at a low altitude over rising terrain was a primary factor in the collision.