On July 6, 1985, a Hughes 369HS (registration N5410W) operated by Rushmore Helicopters, Inc. was involved in an aviation accident near Keystone, SD. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter's main rotor hub and blades separated in flight 279 hours after an overhaul by a repair station not authorized by the manufacturer. The torsion-tension strap pack failed due to fatigue cracking from corrosion pits, with nine failed laminants exceeding the allowable limit of three.
Accident Overview
A helicopter experienced an in-flight failure of the main rotor system, resulting in separation of the main rotor hub and blades. The incident occurred 279 flight hours after the hub had been overhauled. The overhaul was performed by a repair station that was not authorized by Hughes Helicopters for hub overhauls. The helicopter subsequently crashed into a densely wooded area.
Post-Accident Examination
Investigators examined the main rotor system and found that the torsion-tension strap pack had failed. The failure was attributed to fatigue cracking within the stainless steel laminants of the strap pack. Further metallurgical examination showed evidence of corrosion pitting on the laminant surfaces. These corrosion pits served as the initiation points for the fatigue cracks.
Condition of the Strap Pack
The manufacturer specifies a maximum allowable number of laminant failures in any one strap of three. Examination of the failed strap pack revealed that nine laminants had failed due to fatigue.
What happened in the 6 Jul 1985 Hughes 369HS accident near Keystone, SD?
A helicopter's main rotor hub and blades separated in flight 279 hours after an overhaul by a repair station not authorized by the manufacturer. The torsion-tension strap pack failed due to fatigue cracking from corrosion pits, with nine failed laminants exceeding the allowable limit of three.
What aircraft was involved and where did it happen?
The accident on 6 Jul 1985 involved a Hughes 369HS, registration N5410W, operated by Rushmore Helicopters, Inc., at Keystone, SD.
A SkyWalk Join't 3 paraglider crashed into the ground near Las Vizcachas, Chile, on September 1, 2024. The pilot and passenger sustained serious spinal…
PARAPENTE (ULTRALIVIANO NO MOTORIZADO)·2024-09-01DGAC Chile
A Cessna 172N struck electrical cables while on final approach to land at Aucó Aerodrome in Chile. The pilot was uninjured, but the aircraft sustained damage…
A Bombardier DHC-8-402 suffered a tail strike during landing at Puerto Williams on September 9, 2024. All 76 occupants were unharmed, but the aircraft…
A MYD JS-MD 3 glider veered off the runway and struck a wall at Vitacura Aerodrome on January 6, 2025. The pilot was uninjured, but the aircraft sustained…
A recreational paraglider flight in Puchuncaví, Chile, ended with the pilot sustaining serious injuries after a rapid descent and impact with a hillside on…
PARAPENTE (ULTRALIVIANO NO MOTORIZADO)·2025-03-29DGAC Chile
A Tecnam P2006T landed on its belly at an aerodrome in Poland after the crew failed to confirm landing gear deployment. The incident resulted in no injuries…