Goshen, NY, USA
N259TW
ROBINSON R22
According to the pilot, following clutch engagement after engine start and warm up, it took 20 to 25 seconds for the main rotor to start turning. About 15 minutes into the flight and while cruising at 700 feet above ground level, the pilot heard a “flapping” noise and smelled burning rubber. He then “sensed” that the engine was losing power, observed numerous caution lights illuminate, and entered an autorotation. The helicopter subsequently impacted uneven terrain, which resulted in damage to the fuselage, as well as the main and tail rotor blades. Postaccident examination found that both power transmission belts had been ripped, mostly through the center of the backing, separating the two sides of the belt. A review of maintenance records showed that an airframe overhaul was completed about 4 months before the accident, which included replacement of both v-belts.According to the manufacturer’s maintenance manual, a delay of more than 5 seconds between clutch switch engagement and rotor turning indicates excessive belt slack. Power transmission belts that are too loose can jump out of their grooves during start up and jump forward into the next groove or off the forward edge of the pulley. The pre-engine start checklist instructs pilots to adjust the slack of the power transmission belt system so that the rotor begins turning within 5 seconds of clutch engagement. Evidence suggests that the pilot did not perform the recommended check.
On March 22, 2011, about 1315 eastern daylight time, a Robinson R22 BETA, N259TW, was substantially damaged when it impacted the ground following a loss of engine power near Goshen, New York. The certificated private pilot and passenger were not injured. Visual meteorological conditions prevailed and no flight plan was filed for the flight. The flight departed from Ridge Heliport (26NK), Hamptonburgh, NY, about 1300, and was destined for Greenwood Lake Airport (4N1), West Milford, New Jersey. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. During a post-accident interview, the pilot stated that during the engine start, the rotors did not begin to move until about 20 to 25 seconds after he engaged the clutch. About 15 minutes into the flight and while cruising at 700 feet agl, the pilot heard a “flapping” noise and smelled burning rubber. He then “sensed” that the engine was losing power, observed numerous caution lights illuminate and entered an autorotation. The helicopter subsequently impacted uneven terrain, which resulted in damage to the fuselage, as well as the main and tail rotor blades. According to FAA records, the pilot held a private pilot certificate, with a rating for a rotorcraft-helicopter and airplane single-engine land. The pilot reported 2,000 total hours of flight experience; 1,400 hours of which were in rotorcraft. The R22 drive system consisted of a v-belt pulley that was bolted to the output shaft of the engine, an upper pulley connected to the rotor system, and a pair of v-belts that interconnected the two pulleys. Each v-belt consists of two vees incorporated onto a reinforced backing. According to the pre-engine start checklist, pilots were advised to adjust the slack of the v-belt system so that the rotor began turning within five seconds of clutch engagement. The handbook warned that, “Excessive slack may cause the belts to jump out of the pulley grooves during start.” According to Robinson Safety Notice SN-28; “The smell of burning rubber may also indicate an impending belt failure.” A review of maintenance records showed that an airframe overhaul was completed November 4, 2010, which included replacement of both v-belts. Since that time the helicopter had accrued 86.6 flight hours. Following the accident, the v-belts were forwarded to the airframe manufacturer and examined under the supervision of a FAA inspector. Both v-belts had been ripped, mostly through the center of the backing, separating the two vees. The vee of one belt was in two sections. Two of the vees appeared to have been cut and the other sections were separated and exhibited signatures consistent with overload. The vees were mated with the matching vee and the manufacturing and identification markings were legible on both belts. The yellow installation direction arrow was legible on three sections, which indicated the position and direction that the belts were installed. The backing of the aft belt was ripped between the vees and small portions of the backing were missing. The contact surface of both vees appeared to have 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 as the gear was rotating. The backing of the forward belt was ripped between the vees and portions of the backing were missing. The inside contact surface of the forward vee was deformed, consistent with the belt running off of the forward edge of the sheave. This vee was separated in two places and exhibited signatures consistent with overload. The contact surface of the aft vee appeared to have normal wear. Due to the legibility of the direction arrow, identification markings, and pliability of the material the belts were estimated to have accumulated less than 100 hours in service. According to the manufacture’s Maintenance Manual, a delay of more than 5 seconds between clutch switch engagement and rotor turning indicates excessive slack. V-belts that are too loose can jump out of their groves during clutch engagement. The elapsed time between clutch engagement and the main rotor turning was about 20 to 25 seconds according to the pilot.
The pilot’s failure to adhere to published preflight checklist limitations and procedures, resulting in excessive slack and subsequent failure of the power transmission belts and a total loss of rotor system drive.
Source: NTSB Aviation Accident Database
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