ORACLE, AZ, USA
N4006K
Ayres S2R
The pilot configured the aircraft to drop fire retardant over a fire with a planned downhill turn to the left after the release, so as to avoid rising bowl type terrain to the right. He did not release the retardant, when over the fire as expected; instead, he raised the flaps, added power, and turned to the right. During the right turn, he was close to a stall and reportedly encountered a downdraft. He rolled wings level to control a collision with the ground. He did not use the emergency release handle to drop the load. The aircraft was operating near its maximum gross weight, and the density altitude was about 7,700 feet. Examination of the drop system, including the emergency release mechanism, did not indicate a malfunction or failure. A witness flying overhead observed that the aircraft entered the right turn into the bowl area with an estimated airspeed of about 60 knots.
On June 14,1996, at 0822 hours mountain standard time, an Ayres Thrush Commander S2R, N4006K, collided with the ground during fire suppression activities near Oracle, Arizona. The aircraft was destroyed and the single pilot received minor injuries. Visual meteorological conditions existed at the time and no flight plan was filed. The aircraft departed Mesa, Arizona, about 0750. The aircraft is owned and operated by Marsh Aviation International in Mesa and was operating under 14CFR Part 137 for the Arizona State Land Department, Division of Fire Management, at the time of the accident. The pilot stated in his report that he armed the drop system and the 60 percent door while on the base leg and the respective activation lights illuminated. While on final he corrected his line to the right and triggered the drop over the target. He stated he pushed the release button a couple of times. He then retracted the flaps and initiated a right turn to clear the terrain. During the turn, he said he was close to a stall and encountered a downdraft. He then rolled the wings level to control the impact. A witness flying overhead was surprised when the pilot entered the right turn at a slow airspeed estimated at 60 knots. The right turn put the aircraft into a tight bowl and, after about 150 degrees of turn, the aircraft first impacted the terrain with the right wing nearly parallel to the slope. The pilot informed the parties to the investigation in an interview that he originally planned to turn to the left after making the drop and depart through an area with a lower elevation. He said the approach was normal with a slight crosswind and the retardant system was armed with the bleed air prime and the 60 degree door switches on. After the attempted drop, he checked for a red and yellow arm light and turned right because of the right crab angle to correct for the drift. He proceeded to retract the flaps and added full power. He didn't realize he had a problem until he saw the approaching ridge line. He indicated he did not attempt an emergency release using the emergency release control. In the pilot/operator aircraft accident report, a valve was identified as having a malfunction. Examination of the retardant release system and the emergency release system by the parties and the operator did not find any evidence of a mechanical malfunction or failure prior to the accident. This included the control valve, pneumatics, the doors, and the manual release handle. The unofficial temperature at the accident site was reported to be about 89 degrees Fahrenheit. The elevation at the accident site was 4,780 feet msl. At this temperature, the density altitude was estimated to be about 7,700 feet. According to the pilot, the aircraft departed Mesa with full fuel tanks including 350 gallons of fire retardant and 11 gallons of foam. The maximum certificated gross weight for this aircraft was 8,700 pounds. The distance from Mesa to the accident site is about 65 statute miles. According to the operator, the engine uses about 45 gallons of fuel per hour for this type of operation.
the pilot's improper decision to turn toward rising terrain, without releasing or jettisoning the load of fire retardant, while maneuvering at slow airspeed, which resulted in a stall/mush and collision with the terrain. Factors relating to the accident were: the proximity of rising terrain, and high density altitude.
Source: NTSB Aviation Accident Database
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