Mcdonnell Douglas Helicopter 369E N371EE accident near Swan Lake, New York

Probable cause

The pilot's failure to maintain adequate clearance from the power transmission tower structure during powerline maintenance work, which resulted in the helicopter's main rotor striking the lifeline support bracket for the tower catwalk and the subsequent loss of control and collision with terrain.

NTSB analysis

The pilot positioned the helicopter near one of the power transmission tower structures as the lineman, seated on a platform that was attached externally on the skids, began the maintenance. The pilot and the lineman both reported that they then heard a bang, and the helicopter began to shake violently. The pilot maneuvered the helicopter away from the tower and descended through the tree branches. The helicopter came to rest upright in a heavily wooded area.

A microscopic postaccident examination of one main rotor blade tip revealed witness marks consistent with metal impact, and a support bracket for the tower catwalk displayed impact damage. A postaccident examination of the airframe and engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation of the helicopter. A postaccident examination of the tower revealed that, unlike the majority of the towers being maintained, it was equipped with a catwalk which had a lifeline support bracket protruding from the top of it for the tower catwalk. Given this information, it is likely that the pilot did not note this hazard and that main rotor blade tip impacted the tower structure and resulted in the subsequent loss of control.

Text from the NTSB. Open the NTSB docket for ERA21LA262 for the full record.