History of Flight
On March 15, 2011, at approximately 1400 mountain standard time, an experimental Rotorway A-600 Talon helicopter, registration N602RW, made an emergency landing near Chandler, Arizona. The helicopter was substantially damaged during the event. The certificated flight instructor (CFI) and the helicopter-rated pilot under instruction were not injured. The flight was conducted as an instructional flight under Title 14 Code of Federal Regulations Part 91 for transitioning the pilot to the Rotorway helicopter. Visual meteorological conditions prevailed, and no flight plan was filed.
The helicopter had departed Stellar Airpark (P19) in Chandler to practice maneuvers. About 30 minutes into the flight, while flying straight and level at 1,800 feet above mean sea level, the CFI felt a jolt followed by a loud banging noise and strong vibration. He reduced power and searched for a landing site. The engine tachometer indications became erratic, prompting him to further reduce power and initiate an autorotation. Just before touchdown, he added collective to soften the landing. After a brief ground run, the skids dug into the soil, the helicopter pitched nose down, and the main rotor blades contacted the ground. The helicopter then rolled onto its left side. Both pilots exited without assistance, and the CFI shut off the fuel valve and electrical switches.
There were no ground witnesses. The CFI contacted the manufacturer, and company personnel recovered the wreckage later that day. The manufacturer began disassembling the helicopter to determine a possible cause and notified the NTSB the following day. Several days later, an FAA inspector examined the helicopter at the manufacturer's facility.
Personnel Information
The CFI was employed by the manufacturer. He held a flight instructor and commercial pilot certificate with helicopter rating and had approximately 370 total hours of flight experience, all in helicopters. His most recent flight review was in November 2010, and his most recent FAA second-class medical certificate was issued in December 2010.
The pilot under instruction was an Austrian national receiving transition training. He held a private pilot certificate with multiple ratings, including airplane, glider, and helicopter. He had approximately 2,267 total hours of flight experience. His most recent flight review was in January 2011, and his most recent first-class medical certificate was issued in June 2010.
Aircraft Information
The helicopter was an experimental Rotorway A-600 Talon, manufactured from Rotorway components. It was equipped with a Rotorway RI600N 150 hp piston engine. The airworthiness certificate, issued in November 2010, classified it as experimental for "Market Survey / Crew Training." The two-place helicopter had a two-blade main rotor and a two-blade tail rotor.
The engine was mounted vertically behind the cockpit. Normal engine operating speed was about 4,250 rpm. A speed reduction system with an 8:1 ratio used two pulleys and two sprockets, along with belts, to transfer power to the main rotor. A flywheel was attached directly to the engine output shaft, and an engine/drive pulley was attached to the flywheel.
The engine had a history of modifications and zero-timing: originally installed new in another helicopter in June 2009, it was returned to the factory multiple times for modifications and zero-timed each time. The engine was installed in the accident helicopter in February 2011 with a total time (TT) of about 195 hours and 0 hours since major overhaul (SMOH). At the accident time, engine TT was about 215 hours with 20 hours SMOH. The airframe had about 86 hours TT at installation. The most recent inspection was completed on February 24, 2011.
Meteorological Information
Automated weather observation at an airport about 5 miles east of the accident site at 1350 included winds from 180 degrees at 4 knots, visibility 35 miles, a broken cloud layer at 20,000 feet, temperature 27°C, dew point -1°C, and altimeter setting 29.95 inches of mercury.
Wreckage and Impact Information
The accident site was about 6 miles south of P19. Manufacturer personnel recovered the helicopter before notifying authorities, so no on-scene NTSB or FAA investigation was conducted. Photographs showed level, firm desert soil with light scrub. Ground scars from the landing skids extended about 30 feet, ending about 10 feet from the helicopter. The scars indicated initial right skid contact, bounce to left skid, then both skids digging in. The helicopter came to rest facing back toward the scars. The cockpit was intact except for transparencies. Both main rotor blades were crumpled, the tail rotor intact, and the tail boom almost completely severed about 5 feet forward of the tail rotor.
Post-accident examination by an FAA inspector revealed that four screws attaching the engine flywheel to the engine drive pulley had failed, preventing power delivery to the rotor system. The components were sent to the NTSB Materials Laboratory. Optical examination showed fretting and wear on the pulley interface with the flywheel. Both flywheel faces and the pulley attach face had mechanical damage consistent with rotational contact after screw failure. All flywheel screws failed due to fatigue propagation; no metallurgical abnormalities were found with exemplar screws.
Additional Information
The original flywheel-pulley attachment design used three 3/8-inch cap bolts. The modified design on the accident helicopter used four 1/4-inch countersunk machine screws with Phillips heads. Phillips heads have limited torque capacity due to cam-out, which introduces variation in applied torque and preload. The manufacturer did not specify the reason for the design change. At the time of engine assembly in February 2011, the main drive pulley and flywheel were new (0 hours). No records indicated any adjustments or removals since installation. After the accident, the manufacturer reverted to the original attachment method and replaced new-design assemblies with original configuration assemblies.