Accident Details
On August 16, 2018, at approximately 1030 central daylight time, a Schweizer 269C helicopter, registration N3625Z, was destroyed when it was involved in an accident near Kindred, North Dakota. The pilot, who was the sole occupant, was not injured. The helicopter was being operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
Pilot Actions
The pilot reported that while cruising at about 1,000 feet above the ground, he heard a loud "snap" followed by a significant yaw of the helicopter. He immediately pushed the cyclic control forward and lowered the collective. The instrument panel showed a "split needle" indication, meaning the engine speed did not match main rotor speed. The throttle still controlled engine speed, but the main rotor speed did not respond to throttle changes. The engine continued to run normally, and yaw control was maintained through the antitorque pedals. The pilot entered an autorotation and made one revolution while searching for a suitable landing area.
He landed the helicopter level on its skids in a nearby wheat field. However, the helicopter still had forward ground speed, causing it to pitch up briefly before pitching down and slowly rolling onto its right side. After the accident, the pilot moved the mixture control to the fuel cutoff position to shut down the engine. He exited the helicopter without injury and observed smoke emanating from the right side near the damaged right fuel tank. The helicopter caught fire a few minutes later and was subsequently destroyed.
Wreckage Examination
A Federal Aviation Administration (FAA) airworthiness inspector examined the wreckage before recovery. The inspector reported that the forward drive splines of the lower coupling drive shaft were missing and exhibited evidence of significant rotational damage.
Maintenance and Compliance
The FAA inspector interviewed the pilot to confirm which preflight inspection tasks were required for the lower coupling drive shaft. The pilot was unaware of the helicopter’s flight manual preflight checklist requirement to check free-play and verify adequate lubrication of the lower coupling drive shaft. The flight manual stipulates that maintenance be completed before the next flight if excessive free-play or lack of lubrication is observed during a preflight inspection. When the inspector demonstrated how to perform these checks, the pilot stated he had never completed those tasks during the 18 years he had owned the helicopter.
FAA Airworthiness Directive (AD) 93-17-13, dated October 20, 1993, required disassembly and inspection of the lower coupling drive shaft components every 300 hours time-in-service. A review of maintenance and flight records revealed that the helicopter had accumulated about 127 hours since AD 93-17-13 was last completed on September 5, 2013.
Further review showed the helicopter was not in compliance with AD 2017-14-06, which replaced AD 93-17-13 on August 25, 2017. AD 2017-14-06 required disassembly and inspection of the lower coupling drive shaft components within 25 hours time-in-service, and then every 150 hours thereafter. The helicopter had never been inspected per AD 2017-14-06 and had exceeded the initial 25-hour requirement by about 44 hours at the time of the accident.