Firefighting Aircraft Collision with Terrain During Retardant Jettison Attempt (N5198Y)

Incident Overview and Pilot Actions During Flight The aircraft departed and was en route to a nearby forest fire when the pilot reported that the takeoff roll was longer than usual, which he attributed to high temperatures. During the flight, the pilot observed lower propeller rpm and manifold pressure, and the aircraft was descending at a rate of 50 to 100 feet per minute. The pilot determined that the retardant load needed to be jettisoned and made several unsuccessful attempts to use the emergency jettison handle. While the pilot's attention was diverted to jettisoning the load, the aircraft collided with terrain. ## Pre-Takeoff Procedures and Retardant Condition The pilot failed to disengage the emergency release (jettison) handle-locking lever prior to takeoff, as required by the Pilot Operating Handbook. The pilot also chose not to arm the hydraulic power for the retardant gate before takeoff. At the accident site, the slurry mixture was described as having a very thick consistency. The pilot stated that he mixed and loaded the slurry, called Fire-Trol, into the aircraft. The slurry consisted of ammonium phosphate, a clay thickener, a corrosion inhibitor, and a colorant. ## Retardant Testing and Payload Weight A sample of the slurry removed from the sealed pump hose was tested and found to be LCA-R, concentrated retardant unmixed with water. The sample weighed 12.2 pounds per gallon, slightly heavier than pure concentrate, which weighs 12.1 pounds per gallon. No water was found in the sample. When properly mixed, the slurry concentrate should weigh 9.13 pounds per gallon. The aircraft's hopper held 400 gallons, and a properly mixed load should weigh 3,652 pounds. It was computed that the hopper's payload weighed 4,880 pounds at the time of the accident, a difference of 1,228 pounds.