Rotorway A600 N602RW

Summary

On 15 March 2011 at about 21:00 local time, a Rotorway A600 registered N602RW, operated by Rotorway International, was involved in an accident near Chandler, Arizona, United States. 2 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

15 March 2011 at 21:00

Classification

Accident

Location

Chandler, Arizona, United States

Nearest airport

Stellar Airpark (P19)

Coordinates

33.2247, -111.9647

Aircraft

Rotorway A600

Registration

N602RW

Category

Helicopter

Engines

1

Operator

Rotorway International

Operating rule

Part 91: General Aviation

Purpose of flight

Instructional

Phase of flight

Not recorded

Route

Chandler → Chandler

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR11LA167

Nobody was injured.

A design modification that changed the fasteners and components used to attach the main rotor drive pulley to the engine, which resulted in fatigue failure of those fasteners and a complete loss of power to the main rotor.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The flight instructor and a helicopter-rated pilot were conducting the flight for the purpose of transitioning the pilot to the piston-engine experimental helicopter. About 30 minutes into the flight, while flying straight and level, the pilots felt a jolt followed by loud noise and vibration. The flight instructor reduced power and began looking for a place to land. Erratic engine tachometer indications and additional power reduction then prompted the flight instructor to enter an autorotation for a forced landing. The helicopter had some forward velocity at touchdown on the firm, smooth ground. The skids dug in and the helicopter rolled over. Both pilots were uninjured. The helicopter used a system of pulleys and sprockets to enable the engine to drive the main rotor at the desired rotational speed. The accident helicopter incorporated a design change for the main drive pulley attachment to the engine flywheel. The original design used three 3/8-inch diameter socket-head bolts to attach the pulley to the flywheel and one other drive component; the revised design used four 1/4-inch diameter cross-slot (Phillips) screws to attach the pulley only to the flywheel. Postaccident examination of the components revealed that the four attach screws had failed due to fatigue. Laboratory examination of other screws from the same manufacturing lot indicated that the screws were in compliance with their design specifications. The failed screws had about 20 hours in service. The torque that could be applied to the cross-slot screws was limited by the slippage of the screwdriver in the screw head, which in turn limited the preload on the screws and the induced friction in the pulley-to-flywheel joint. Those conditions contributed to the cyclic loading of the fasteners, which then resulted in their fatigue failure. Subsequent to the accident, the manufacturer reverted to its original flywheel-pulley attach method and replaced the newer design pulley assemblies with the original configuration.

Quoted verbatim from the NTSB record.