ERA23LA205

After the instructional flight was airborne for slightly more than an hour, the helicopter began descending slightly followed by repetitive low main rotor rpm warnings. The student corrected after the first two warnings, but did not correct after the third. The flight instructor took over the controls and rolled the throttle slightly off, then opened it all the way to the stop, recovering the engine rpm. The flight instructor then initiated a precautionary landing and turned toward an open field. During the descent, when operating in the shaded area of the height velocity diagram (between 100 and 200 ft above the ground and 40 knots airspeed ), the low main rotor rpm again sounded. Knowing the helicopter was flying in the shaded area of the height velocity diagram, the flight instructor nosed the helicopter over to increase airspeed and entered an autorotation. About 40 to 50 ft above ground level (agl), he started a slight deceleration though the helicopter was in a near-vertical descent. He leveled the helicopter at a height of about 10 to 20 ft agl while rapidly approaching the ground. He applied collective to cushion the landing but landed hard, damaging all main rotor blades and the tail boom. Following the accident, the engine was started twice and operated to partial power (due to the main rotor blade damage), with no anomalies noted. The reason for the reported loss of engine power could not be determined from the available evidence.

On April 22, 2023, about 1230 eastern daylight time, a Schweizer 269C, N789LH, was substantially damaged when it was involved in an accident near Springfield, Tennessee. The flight instructor and pilot undergoing instruction (PUI) were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations part 91 instructional flight. The flight instructor had flown the helicopter about 1.4 hours earlier in the day with no engine issues. Before the accident flight, he performed a preflight inspection, an engine run-up, and a hover/power-before-takeoff check with no engine issues noted. The flight instructor further stated that after liftoff they performed 15 to 20 minutes of hover work, then departed the Springfield Robertson County Airport (M91), Springfield, Tennessee, via runway 22 for right traffic, remaining in the airport traffic pattern. On the third pattern, he decided to depart to the west for airwork. After about 15 minutes he decided to fly to a confined area east of M91. When the flight was transitioning west to east, about 3 nautical miles south of M91 and flying between 1,200 to 1,400 ft mean sea level (500 to 700 ft above ground level), he noted that the main rotor (MR) rpm was low and heard the horn and announced, “Rotor RPM.” The PUI made a correction, but almost immediately had low MR rpm. He announced the low MR rpm to the PUI, who made a correction. On the third time in a short span (possibly 15 to 30 seconds between each event), he announced low MR rpm, but the PUI didn’t appear to make a correction. At this point the flight instructor attempted to increase rpm via throttle manipulation, but he noted the throttle was fully engaged, though they still had low rpm at around 2,950. He noted the engine rpm could increase to about 3,050 if he pushed against the limiting spring in the throttle. He announced, “I have the controls” and took the controls from the PUI, made a slight reduction in throttle, noted the drop in rpm, and immediately increased throttle all the way to the stop, regaining about 3,050 rpm. He did not remember seeing a split in engine and rotor rpm throughout the event. The flight instructor further stated that he informed the PUI of the need to perform a precautionary landing. He turned towards the nearest field and started a normal approach, which began between 200 and 300 ft agl. During the descent, with the throttle fully engaged against the spring, he heard the low MR rpm alarm sound; the MR rpm was now around 2,900. While at about 40 kts and 100 to 200 ft agl, he announced his intention to the PUI of performing an autorotation and simultaneously lowering the collective with the throttle fully engaged. He nosed the helicopter over to an accelerative attitude to gain airspeed knowing they were flying in the shaded area of the height/velocity diagram. He reported that, upon entering the autorotation, he remained focused outside and that he announced, “Mayday” on the airport common traffic advisoryfrequency. At about 40 to 50 ft agl he started a slight deceleration, though the helicopter was in a near-vertical descent. He leveled the helicopter at about 10 to 20 ft agl and, as they rapidly approached the ground, he applied collective to cushion the landing. On ground contact, which was described as a hard landing, the helicopter came to an immediate stop. Due to the hard landing, the main rotor blades dipped and contacted the tail boom, damaging both. Postaccident examination of the airframe revealed the skids were spread out, all three main rotor blades were damaged, and the tail boom was partially separated and bent at a 90° angle to the right side of the helicopter. Postaccident examination of the engine by the owner with FAA oversight revealed the engine contained sufficient oil with an adequate supply of fuel. The sprag clutch was checked with no discrepancies noted. The owner started the engine and operated it for about 3 to 5 minutes, to about 1,600 rpm because they could not engage the main rotor. The engine was also operated a second time also to about 1,600 rpm with no discrepancies reported by the FAA inspector who witnessed the engine run. The reason for the reported loss of engine power could not be determined from the available evidence despite twice operationally testing the engine.