Accident Overview
On June 12, 2015, about 1215 central daylight time, a Grumman-Schweizer G164B airplane, registration N48687, nosed over during a forced landing following a loss of engine power during an aerial application maneuver near Foster, Nebraska. The commercial pilot sustained minor injuries. The airplane empennage was substantially damaged during the nose over. The airplane was operated under 14 Code of Federal Regulations Part 137 as an aerial application flight. Day visual flight rules conditions prevailed, and the flight did not operate on a flight plan. The local flight originated from Bloomfield Municipal Airport (84Y), near Bloomfield, Nebraska, about 1100.
Pilot Account
According to the pilot's accident report, the airplane departed with two hours of fuel on board. The terrain of the field he was spraying was flat with scattered trees, and the ground was muddy and water logged. All gauges indicated in the green. During his last turn to conduct a pass on the pasture head land, the engine stopped producing power at an altitude of about 100 feet. He leveled off, checked that magnetos were on, mixture rich, fuel valve on, and moved the throttle to full. Noting airspeed falling, he applied forward stick pressure to regain airspeed. Unable to reach the nearest road, he landed in an adjacent pasture. As the wheels touched down, the airplane slowed, reducing lift and putting more weight on the main wheels. The wheels sank into the mud, causing the airplane to nose over onto its top.
During a post-accident inspection, the fuel quantity gauge, part number A5587-1, was found to be indicating incorrectly. When the airplane was refueled via the remote single point port to full as indicated on the gauge, the tanks were only 3/4 full. When the gauge read 1/4 full, the fuel system was actually empty.
Fuel System and Gauge Issues
Another operator described the fuel system: all models of the Ag Cat (G164, G164A, G164B, G164C, G164D) rely on a mechanical fuel gauge in the bottom of the center section fuel tank. Configurations vary with additional wing tanks, but all tanks connect and the engine draws from the center section. The single fuel gauge indicates the level of the entire system. There is one fuel filler neck and cap in the center section. With a bottom point fuel system modification, valves and hoses allow fueling from the ground. Fuel quantity gauges are generally checked for accuracy when full and empty, but partial readings fluctuate during maneuvering. The operator also noted reports of Ag Cat fuel quantity gauges slipping a tooth in the gearing system, giving false indications. The fuel filler cap can be opened and a stick used to check fuel level, but the single point fueling system was designed to eliminate climbing onto the wing for visual checks.
According to a fuel gauge manufacturer's brochure, the gauge was a senior liquid level, bottom mount, side view dial gauge, with the float operating the dial through gear action.
Manufacturer Information
The airplane flight manual specifies pre-flight checks including opening the fuel cap and visually checking fuel level and color, observing the fuel gauge for proper reading, and draining sumps. The manufacturer acquired the AgCat program in 1998 and sold 600 A5587-1 units. Of those, 400 had been removed for reasons including stained dial faces, sunk floats, movement obstructions, or being worn out. The manufacturer stated that the gauge should not be considered fuel quantity verification, and flight manuals include fuel quantity and fuel gauge checks as pre-flight procedures. The accident pilot confirmed that he relied on the fuel gauge indication and did not stick the tank before departure.