CHI06LA124 · Hughes 269B

The helicopter was substantially damaged when a tail boom support fitting failed during cruise flight, which resulted in a secondary failure of the tail rotor drive shaft. The pilot initiated an autorotation and encountered a ditch during touchdown, causing the right skid to collapse. The pilot reported that the helicopter was in cruise flight when he heard a "very loud" bang. He stated that the aircraft began to yaw and he subsequently determined the aircraft had no tail rotor authority. He set up for a run-on landing to a field; however, he subsequently heard a "metal grinding sound" and a "high pitched squealing noise." He initiated an autorotation at that time. The pilot reported a "sensation of the tail boom swinging left [and] right, up [and] down." The helicopter encountered a ditch during touchdown, which collapsed the right skid. Upon exiting the helicopter, the pilot noticed that the left main tail boom support (cluster) fitting had broken loose from the frame. The tail rotor drive shaft and cluster fitting were examined by the National Transportation Safety Board Materials Laboratory. Damage to the tail rotor drive shaft was consistent with an overstress failure and appeared to be caused by rotational contact between the drive shaft and the forward tail boom closure fitting. The cluster fitting exhibited fracture markings indicative of fatigue. Fracture features on both lugs indicated localized fatigue origin areas on the outer surfaces of each lug. Federal Aviation Administration (FAA) Airworthiness Directive (AD) 2003-13-15 R1, which became effective August 10, 2004, was applicable to the accident aircraft. The AD noted that compliance was required in order "to prevent failure of a tailboom support strut or lug on a cluster fitting." The AD required modification or replacement of the original cluster fittings, part numbers 269A2234 and 269A2235, within 6 months or 150 hours time-in-service (TIS). The AD required dye penetrant inspections of the lugs within 10 hours TIS, and thereafter at intervals not to exceed 50 hours TIS, until the lugs were modified or replaced. Nominal measured lug thickness was 0.076 inch, which was consistent with the original cluster fitting configuration. The failed lug did not appear to have been modified and did not appear to be in compliance with the AD. Review of the aircraft logbook revealed that a 100 hour / annual inspection was completed on May 23, 2005. The inspection entry noted AD 2003-13-15 R1. In addition, the airworthiness compliance record noted that the AD had been complied with by performing a dye penetrant inspection without finding any cracks. The entry also stated that the modification kit was not installed at that time.

Verbatim NTSB analysis and probable cause from the NTSB dataset