Accident Overview
On April 22, 2023, at about 1230 eastern daylight time, a Schweizer 269C, registration N789LH, was substantially damaged during a hard landing near Springfield, Tennessee. The helicopter was conducting an instructional flight under Title 14 Code of Federal Regulations Part 91. The flight instructor and the pilot undergoing instruction (PUI) were not injured.
Sequence of Events
Earlier that day, the flight instructor had flown the helicopter for about 1.4 hours with no engine issues. Prior to the accident flight, a preflight inspection, engine run-up, and hover/power-before-takeoff check were completed without any issues. After takeoff from Springfield Robertson County Airport (M91) via runway 22, the flight performed 15 to 20 minutes of hover work and then entered the traffic pattern. On the third pattern, the instructor decided to depart west for airwork. After about 15 minutes, he chose to fly to a confined area east of M91.
During the transition from west to east, about 3 nautical miles south of M91 at an altitude between 1,200 and 1,400 feet mean sea level (500 to 700 feet above ground level), the instructor noticed low main rotor (MR) rpm and heard a warning horn. He announced "Rotor RPM." The PUI made a correction, but almost immediately the MR rpm dropped again. The instructor announced the low rpm again, and the PUI corrected. A third time, within 15 to 30 seconds, the instructor announced low MR rpm, but the PUI did not appear to correct. The instructor then attempted to increase rpm by manipulating the throttle but found it fully engaged; however, rpm remained around 2,950. He noted that pushing against the limiting spring could raise engine rpm to about 3,050. He announced "I have the controls," reduced throttle slightly, observed a drop in rpm, then immediately increased the throttle to the stop, regaining about 3,050 rpm. He did not observe a split between engine and rotor rpm throughout the event.
The instructor informed the PUI of the need for a precautionary landing and turned toward the nearest field, starting a normal approach from 200 to 300 feet agl. During the descent, with the throttle fully engaged against the spring, the low MR rpm alarm sounded as rpm fell to about 2,900. At about 40 knots and 100 to 200 feet agl, the instructor announced his intention to perform an autorotation, simultaneously lowering the collective with the throttle still fully engaged. He nosed the helicopter over to gain airspeed, knowing they were in the shaded area of the height-velocity diagram. Upon entering the autorotation, he focused outside and announced "Mayday" on the airport common traffic advisory frequency. At about 40 to 50 feet agl, he began a slight deceleration, though the helicopter was in a near-vertical descent. He leveled the helicopter at 10 to 20 feet agl and, as the ground approached rapidly, applied collective to cushion the landing. The helicopter contacted the ground in a hard landing and came to an immediate stop. Due to the impact, the main rotor blades dipped and struck the tail boom, damaging both.
Postaccident Examination
Postaccident examination revealed the skids were spread out, all three main rotor blades were damaged, and the tail boom was partially separated and bent 90 degrees to the right. The owner, under FAA oversight, examined the engine and found sufficient oil and an adequate fuel supply. The sprag clutch was checked with no discrepancies. The engine was started and operated for 3 to 5 minutes at about 1,600 rpm (without main rotor engagement) and again to 1,600 rpm with no anomalies reported by the FAA inspector who witnessed the run. Despite these operational tests, the reason for the reported loss of engine power could not be determined from the available evidence.
Probable Cause
The probable cause of the accident could not be determined from the available evidence.