Accident Sequence
During a fire retardant drop operation, the airplane was conducting a third pass after a practice dry run and a go-around on the second pass. The pilot communicated downwind, base, and final on the third pass but made no further transmissions and did not report any problems. The drop occurred at approximately 100 feet above ground level over terrain that sloped downward about 20 degrees through the drop zone. After the retardant was released, the airplane's nose pitched up about 10 degrees, a normal reaction to the shift in center of gravity. Approximately two seconds later, the nose pitched down about 45 degrees, and the airplane maintained this attitude until it struck the ground.
Drop Pattern and Witness Observations
Witnesses observed the retardant exiting the airplane, but the drop was not at the intended point and was not distributed in an even line, unlike previous drops by the same pilot. The drop pattern was angled about 10 degrees to the final approach course, and the pattern was wide and heavy at the beginning and narrow and thin at the end. This pattern indicated that the pilot initiated the drop early while still turning onto final.
Post-Impact Examination
Examination of the wreckage revealed a prominent bend in the propeller shaft and a twist in the vertical splines, indicating that the engine was generating high power at impact. No anomalies were found in the flight control system. Stall speeds for the airplane, equipped with vortex generators, ranged from 73 mph in the clean configuration to 72 mph with full flaps.
Operational Considerations
Drop techniques, airspeed, and flap settings varied among pilots of this type. Some pilots flew at airspeeds of 85 to 90 mph to reduce the pitch-up effect during pullout. The aircraft's operator manual noted that a sudden shift in center of gravity at retardant release would cause the airplane to pitch up and could decrease airspeed by as much as 12 mph.