N248LF

On June 13, 1997, approximately 1300, central daylight time, an Air Tractor AT-502A agricultural airplane, N248LF, owned and operated by Lissie Flying Service, Lissie, Texas, was substantially damaged during landing roll out at a private agriculture airstrip, near Chesterville, Texas. The commercial pilot, sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the Title 14 CFR Part 137 aerial application flight.

The pilot reported that he had just landed about 200 feet beyond the approach end of the northwest oriented 2,600 foot runway. About 2/3 to the end of the runway, he applied reverse power, "but did not receive any reversing action." After applying full reverse, "the prop sounded like it was going to flat pitch." In an attempt to "go around" he pushed the power lever to full forward, but did not get any response. Another attempt was made to apply reverse with no response. As the airplane approached the departure end of the runway, the pilot applied left brakes to intentionally ground loop to avoid hitting parked trucks at the departure end of the runway. Subsequently, the right main landing gear sheared and the airplane skidded into a ditch adjacent to the left side of the runway.

On site examination of the airplane by a FAA inspector revealed that the right wing spar web was structurally damaged. External examination of the engine, engine accessory gearbox, and propeller assemblies did not reveal any obvious pre-impact anomalies. Further external examination of the propeller piston and the propeller governor did not reveal any oil leaks.[Note: Propeller blade pitch is actuated by oil pressure within the piston assembly] All cockpit power control quadrant linkages were found to be intact, and the reverse detent on the thrust lever housing operated normally when cycled.

At the request of the NTSB investigator-in-charge, the operator coordinated a teardown of the propeller assembly, and a functional bench test of the propeller governor. The propeller assembly, which was overhauled approximately 6 months prior to the accident, did not reveal any defects during the teardown examination. The propeller governor, which was recently installed and had a total time since overhaul of 31.2 hours, did not show any abnormalities during the bench tests that would have contributed to the accident. However, it was noted in the test results that the underspeed setting @ 3,000 engine RPM, was found to be 1.5 PSI. According to manufacturer's specifications, the underspeed setting @ 3,000 RPM should be 4.0 PSI. According to the bench test technician, the lower underspeed PSI setting would not inhibit propeller reversing capability.