History of Flight
On September 20, 2017, at 1309 Pacific daylight time, a Robinson R22 Beta helicopter, registration N7514S, landed hard and rolled over following an autorotation at Long Beach Airport (Daugherty Field), Long Beach, California. The student pilot sustained serious injuries, and the helicopter sustained substantial damage. The helicopter was registered to Spitzer Helicopter LLC and operated by Revolution Aviation under Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and no flight plan was filed. The local flight departed Long Beach about 1305.
The student departed earlier that morning with his instructor from their operational base in Santa Ana, California. They planned to fly to Long Beach Airport, where the instructor would disembark, and the student would perform solo maneuvers and flights in the traffic pattern. After arriving at Long Beach and landing on helicopter pad 1, they performed a pedal turn to assess helicopter performance with a left crosswind, then departed for a traffic pattern flight. After landing, the instructor exited and waited on the grass adjacent to the pad. He watched the student perform low hovering maneuvers uneventfully. Other helicopters in the area had departed, and the student and instructor agreed that the student should depart, perform one circuit in the traffic pattern, and land on pad 3, a larger pad the student was more familiar with.
The departure and landing were uneventful; once on the ground, they exchanged thumbs-up, and the student departed for another pattern flight. The instructor reported the flight appeared normal, with appropriate descent path and speed during approach. However, as the helicopter neared the pad, it slowed. The instructor thought the student would land just short of the pad, but the nose yawed left and right by a few degrees, and the helicopter suddenly began a rapid, uncontrolled descent, as if all lift were lost. The helicopter struck the ground slightly left-side-low and rolled onto its right side.
The student recalled similar observations: approaching within about 40 ft of the pad, the helicopter shuddered, then the low rotor RPM horn sounded. He immediately lowered the collective and initiated an autorotation. Just before striking the ground, he pulled back on the cyclic but did not apply collective control. He did not hear unusual engine sounds and did not check engine or rotor tachometer during the event.
Personnel Information
The student pilot held a third-class aviation medical certificate issued on July 27, 2017. After the accident, he reported 45 total flight hours, all in helicopters, including 2 hours of solo flight time.
Aircraft Information
The helicopter was manufactured in 2002 and equipped with a Lycoming O-360-J2A engine, serial number L-37717-36A. On May 9, 2012, a helicopter overhaul and engine rebuild were completed. A 100-hour inspection was completed on August 25, 2017, about 20 flight-hours before the accident. During the inspection, the engine's no. 1 cylinder was removed due to low compression, repaired, and re-installed. At inspection, the airframe and engine had accumulated 1,370.4 flight hours since overhaul/rebuild.
The most recent maintenance event was for an inspection following a rotor blade overspeed (below 114%). The inspection was completed on September 8, 2017, about 10 flight-hours before the accident.
The helicopter was equipped with a governor system designed to maintain engine speed by sensing changes and applying corrective throttle control inputs through a friction clutch. The system could be overridden by manual throttle manipulation. The governor switch was found in the "ON" position at the accident site.
Meteorological Information
A special aviation routine weather report issued immediately after the accident indicated wind from 170° at 9 knots. Pad 3 is oriented east-west, and left traffic pattern was in use, resulting in an almost direct left crosswind during the landing approach.
Additional Information
The FAA Helicopter Flying Handbook discusses transverse flow effect, which can cause increased vibrations at airspeeds just below effective translational lift and may require a cyclic input to the left to counteract. The handbook also notes that during normal landing approaches, helicopters require near maximum power to land.
The Pilot's Operating Handbook (POH) describes procedures for power loss at all altitudes and autorotations to power recovery, instructing the pilot to raise the collective just before touchdown to cushion the landing. For activation of the stall warning horn and caution light, the POH states: "A horn and an illuminated caution light indicate that rotor RPM may be below safe limits. To restore RPM, immediately roll throttle on, lower collective and, in forward flight, apply aft cyclic."
Tests and Research
The helicopter was examined by the NTSB investigator-in-charge and technical representatives from Robinson Helicopter Company (RHC). Drivetrain and flight control continuity were established. The engine did not exhibit indications of catastrophic failure. Spark plugs showed normal operation deposits and wear. The crankshaft rotated by hand established mechanical rotational continuity; valves and rockers moved freely with equal amounts; cylinder compression was obtained on all cylinders in proper firing order; sparks were observed at each spark plug lead.
The upper frame sustained crush damage, causing the upper sheave to meet frame tubes adjacent to the clutch actuator. Rotational scoring was observed on the outer radius of the sheave and corresponding frame tubes, consistent with engine operation at impact.
The governor controller was tested at RHC facilities according to factory calibration and functional test specifications and passed all tests.