Factual Information
On March 22, 2011, at approximately 1315 eastern daylight time, a Robinson R22 BETA (registration N259TW) was substantially damaged when it impacted the ground near Goshen, New York, after the pilot experienced a loss of engine power. The private pilot and a passenger were not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight departed from Ridge Heliport (26NK) in Hamptonburgh, New York, around 1300, destined for Greenwood Lake Airport (4N1) in West Milford, New Jersey. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Information
The pilot held a private pilot certificate with ratings for rotorcraft-helicopter and airplane single-engine land. He reported 2,000 total flight hours, including 1,400 hours in rotorcraft.
Aircraft and Drive System Information
The Robinson R22 drive system comprises a v-belt pulley bolted to the engine output shaft, an upper pulley connected to the rotor system, and a pair of v-belts connecting the pulleys. According to the pre-engine start checklist, pilots should adjust belt slack so that the rotor begins turning within five seconds of clutch engagement. The handbook warned that excessive slack could cause the belts to jump out of the pulley grooves during start. Robinson Safety Notice SN-28 stated that the smell of burning rubber might indicate an impending belt failure.
Sequence of Events
During engine start, the rotor did not begin moving until about 20 to 25 seconds after the pilot engaged the clutch. Approximately 15 minutes into the flight, while cruising at 700 feet above ground level, the pilot heard a flapping noise and smelled burning rubber. He then sensed the engine losing power, observed multiple caution lights illuminate, and initiated an autorotation. The helicopter impacted uneven terrain, resulting in damage to the fuselage, main rotor blades, and tail rotor blades.
Maintenance History
An airframe overhaul was completed on November 4, 2010, which included replacement of both v-belts. Since that overhaul, the helicopter had accumulated 86.6 flight hours.
Post-Accident Examination of V-Belts
The v-belts were forwarded to the manufacturer and examined under the supervision of a Federal Aviation Administration inspector. Both belts were ripped, mostly through the center of the backing, separating the two vees. One vee was in two sections. Two vees appeared to have been cut, and the other sections exhibited signatures consistent with overload. The vees were matched with their counterparts, and manufacturing markings were legible. The yellow installation direction arrow was legible on three sections, indicating the belts' position and direction of installation.
The backing of the aft belt was ripped between the vees with small portions missing, and the contact surface of both vees showed normal wear. The forward vee had two areas of abnormal abrasion on the inner contact surface, consistent with the vee lying across the starter ring gear while it was rotating. The backing of the forward belt was also ripped, with portions missing. The inside contact surface of the forward vee was deformed, consistent with the belt running off the forward edge of the sheave. This vee was separated in two places and showed overload signatures. The contact surface of the aft vee had normal wear. Based on legibility of the direction arrow, identification markings, and material pliability, the belts were estimated to have accumulated less than 100 hours in service.
According to the manufacturer's maintenance manual, a delay of more than five seconds between clutch switch engagement and rotor turning indicates excessive slack. The pilot reported a delay of about 20 to 25 seconds.