Accident Overview
On June 20, 2008, at approximately 1400 central daylight time, an Ayres S2R-G6, registration N61374, operated by Swan Lake Flying Service, Inc., was substantially damaged when it struck trees and impacted terrain during a forced landing. The accident occurred near Pine Bluff, Arkansas, following a loss of engine power. The commercial pilot, who was the sole occupant, was not injured. Visual meteorological conditions prevailed at the time of the accident. The aerial application flight was conducted under Title 14 Code of Federal Regulations Part 137 without a flight plan. The local flight had originated at approximately 1330 from Altheimer, Arkansas.
Pilot Account
The pilot reported that he was spraying a rice field with fertilizer when the airplane began to lose altitude. He attempted a forced landing in an open bean field. During the landing, the right wing clipped a tree, causing the airplane to spin to the right. The airplane impacted terrain sideways, shearing off the landing gear. The wings were bent and the fuselage was buckled.
Investigation Findings
FAA inspectors from the Little Rock Flight Standards District Office examined the airplane. The fuel remaining in the engine fuel filter housing was clean and clear. The fuel pressure line fitting on the filter housing had stripped threads, allowing the fitting to wobble about 5 to 10 degrees. When moved, the O-ring would not seat. No fuel residue was found on adjacent cowling structure, indicating that the fitting damage occurred during impact and was not pre-existing.
The engine was removed and shipped to Honeywell in Phoenix, Arizona. Under FAA auspices, it was disassembled and examined on October 8 and 9, 2008. Honeywell reported that the type and degree of engine damage indicated it was not operating at the time of impact. No pre-existing condition was found that would have caused a loss of power or an in-flight shutdown.
Previous Incident and Design Issue
FAA inspectors later learned that about six flights before the accident, the airplane had experienced an uncommanded engine shutdown while being refueled and reloaded. Ayres, in the design process, had not installed engine speed switches for automatic electronic control of the fuel system. Instead, pilot-activated switches provided manual control. Examination of the wiring schematic revealed that a short in the wires or a contaminated or corroded switch could send voltage to pin "B" on the Fuel Shutoff Solenoid Valve, causing it to close. In the case of N51374, there was evidence of wiring and fuel shutoff switch contamination.
A safety recommendation proposal was submitted as a result of the investigation.