NTSB Identification: ERA10LA238
14 CFR Part 133: Rotorcraft Ext. Load
Accident occurred Wednesday, April 21, 2010 in Newfane, VT
Probable Cause Approval Date: 07/18/2011
Aircraft: MCDONNELL DOUGLAS HELICOPTER 369E, registration: N400MB
Injuries: 2 Serious.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The accident occurred during a procedure to install a hold-down block onto a pulling rope located between powerline structures. An all stop order to quit pulling the rope was reportedly given 3 to 5 minutes before the accident and confirmed by the pilot via radio before maneuvering to begin the hold-down block installation. No movement of the pulling rope was reported by personnel associated with the installation. The pilot confirmed there was adequate clearance to work and positioned the helicopter near one of the structures as the additional lineman in the helicopter installed the hold-down block. After completion, the lineman in the helicopter saw two waves in the pulling rope. The first wave missed the helicopter but the second wave contacted the main rotor blade, wrapping around the main rotor mast. The lineman jumped into the helicopter, which descended to the ground and came to rest on its left side nearly inverted. The operator reported that there was no preimpact mechanical failure or malfunction with the helicopter. No determination could be made as to the reason for the reported wave in the pulling rope.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The pilot's inadvertent encounter with a rope while maneuvering during powerline operations for undetermined reasons.

Full narrative available

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