Overview
On May 26, 2021, at about 1430 Pacific daylight time, a Boeing A75N1 Stearman, registration N75016, was substantially damaged during an accident near Frazier Lake Airpark (1C9) in Hollister, California. The pilot and a pilot-rated passenger sustained minor injuries. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Sequence of Events
The pilot had purchased the airplane six days prior and contracted a local maintenance shop to perform an annual inspection. After the inspection, the airplane was returned to service, and the pilot received a thorough walkaround and preflight briefing. On the day of the accident, the pilot and passenger completed a preflight inspection and engine run-up with no anomalies. They performed ten full-stop takeoffs and landings, then flew to Hollister Municipal Airport (CVH) to refuel. After returning to 1C9, the pilot conducted another takeoff and landing. During the subsequent initial climbout, the engine rpm began decreasing, and the airplane stopped gaining altitude. The pilot estimated the altitude at about 600 feet above ground level. The passenger reported the airplane was neither gaining nor losing altitude and verified that the propeller lever, throttle lever, mixture control lever, and fuel selector were in correct positions. The pilot noted that although rpm was dropping, the engine never lost complete power. Shortly after, the pilot initiated a right turn to avoid telephone lines and executed a forced landing in a soft dirt field approximately 0.3 nautical miles from 1C9. The airplane came to rest upright, and the lower portions of both wings sustained substantial damage.
Postaccident Examination
Postaccident examination of the wreckage revealed no preimpact anomalies or mechanical failures with the airframe. A subsequent engine run-up performed at the scene showed no anomalies. A follow-up examination of the engine also found no preimpact mechanical failures. Attention then focused on the propeller governor, which was removed for testing. Maintenance logbooks indicated the governor had not been overhauled, and the records did not reveal when it was last serviced.
Governor Analysis
External examination of the governor showed no body damage, and the drive gears turned freely. No metal or contaminants were observed in the oil when the gears were manually rotated. The flywheel assembly, pilot valve, and thrust bearing were unremarkable. Bench testing revealed a high rpm setting of 2,400 rpm and a relief pressure setting of 125 psi. Manufacturer specifications call for a high rpm setting of 2,300 rpm and a relief pressure of 180 to 200 psi. In a feather setting, the governor produced 1,200 rpm, which was within manufacturer limits. Internal leakage and pumping capacity were within acceptable ranges. A lag was observed as rpm rose when the simulated throttle setting increased; conversely, no lag occurred when throttle decreased. A teardown of the relief valve assembly revealed that the relief valve spring was shorter than an exemplar spring. No broken pieces were found. The spring was replaced with a standard-length spring, and the governor was bench tested again, producing 200 psi in relief pressure, with no lag observed when throttle increased.