SEA96LA172

Immediately after takeoff, the pilot began a turn which took him within 75 feet of an operating agricultural irrigation spray device. This device was located 500 feet from the takeoff runway. The pilot reported that as he passed the device, the water stream from the device pivoted and shot a two-to-three-inch stream of water directly in front of the engine air intake of the turboprop-engine-equipped aircraft, resulting in engine flameout. This occurred at an altitude of about 75 feet above ground level. A forced landing was then made in a wheat field, where the airplane nosed over.

On July 27, 1996, approximately 0700 mountain daylight time, a Grumman-Schweizer G-164A, N5390, registered to Buzz Ruchert Flying Service of Pomeroy, Washington, was substantially damaged in a forced landing in a wheat field following a loss of engine power immediately after takeoff from a private airstrip approximately 7 miles south of Dubois, Idaho. The commercial pilot of the single-seat agricultural aircraft was not injured. The 14 CFR 137 local agricultural aerial application flight was not on a flight plan. Visual meteorological conditions prevailed, according to the pilot.

The airplane had a Garrett TPE331-1 turboprop engine conversion installed. The pilot stated that immediately after takeoff to the south, he began a right turn back to the north. After completing about 90 degrees of turn, while at an altitude of about 75 feet above ground level, he passed about 75 feet from a pivoting irrigation device which was spraying. This device was located approximately 500 feet southwest of the takeoff runway. The pilot stated that as he passed the device, the water stream from the device pivoted around and "shot a [two to three inch] stream of water directly in front of the engine air intake resulting in flame out." The ensuing forced landing was made into a "waist high, thick mature wheat field in sandy soil...." The airplane nosed over during the forced landing into the wheat. On his accident report, the pilot recommended an auto-relight system triggered by negative torque sensing, and avoidance of flight near high-output sprinkler systems with turboprop aircraft, as possible ways that the accident could have been prevented.

A representative of the AlliedSignal Engines air safety investigation department, in a telephone conversation with the NTSB investigator-in-charge (IIC), stated that a water ingestion tolerance test had been accomplished on a TPE331-16 engine on a previous occasion, in conjunction with another accident investigation. He stated that the test consisted of spraying a water stream from a fire hose into the intake of an operating engine. The AlliedSignal representative stated that the engine continued to run under those conditions, but that the TPE331-16 has a larger compressor than the TPE331-1.

On his accident report, the pilot (who was also a co-owner of the aircraft) reported that the engine had 457 hours in service since inspection of the hot section and gearbox, and 3,510 hours since overhaul. The AlliedSignal Engines representative stated to the NTSB IIC that the TPE331 engine has a recommended time between overhauls of 3,000 hours, which may be extended to 3,600 hours if certain service bulletins are accomplished. It was not determined whether the applicable service bulletins had been accomplished on the accident engine.

Per 14 CFR 33.77, the following airworthiness standards are applicable to the design and construction of turbine aircraft engines with respect to tolerance to water ingestion: "Ingestion of water...under the conditions prescribed in...this section, may not cause a sustained power or thrust loss or require the engine to be shut down. It must be demonstrated that the engine can accelerate and decelerate safely while inducting a mixture of at least 4 percent water by weight of engine airflow following stabilized operation at both flight idle and takeoff power settings with at least a 4 percent water-to-air ratio." The regulation specifies that the engine must be capable of ingesting at least 4 percent water by weight of engine airflow, sucked into the engine, for 3 minutes each at flight idle and takeoff, and "during acceleration and deceleration in spray to simulate rain."