Accident Overview
On July 26, 2013, about 1230 central daylight time, an Enstrom F-28A helicopter, registration N287Q, was substantially damaged when it struck the ground near Danbury, Texas. A postimpact fire ensued. The flight instructor sustained serious injuries, while the private pilot received minor injuries. The helicopter was registered to and operated by Salaika Aviation LLC under 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed, and the flight operated without a flight plan. The accident occurred at the beginning of the flight.
Flight Sequence
The flight instructor reported that he had conducted two uneventful flights earlier that day with no mechanical anomalies. He refueled the helicopter, confirming 25 gallons of fuel aboard. After warm-up and pre-takeoff checks, the private pilot hover taxied the helicopter to runway 24 and departed. As the helicopter climbed through 200 feet, the private pilot initiated a crosswind turn. At approximately 300 feet, during a right turn to the downwind, a loud sound described as a "gun shot" and ricocheting metal was heard by both pilots, originating directly behind their heads. Simultaneously, the collective control became unresponsive.
The flight instructor immediately took control and attempted to land. Lowering the collective had no effect; the collective "moved freely in [his] hand with no resistance or effect on the helicopter." He set up for a long, shallow approach to a helipad over an open field. During a turn at 60 knots indicated airspeed, the helicopter began oscillating vertically. Popping sounds were heard, and oscillations intensified. Main rotor rpm decreased; lowering the collective and increasing the throttle produced no response, and rotor rpm continued to drop. The helicopter shook violently, and the flight instructor observed that the blade pitch was very high. Control was lost, and the helicopter impacted the ground moments later.
Examination Findings
Investigators from the National Transportation Safety Board (NTSB) examined the fractured and fire-damaged components, including the collective push-pull rod assembly, cyclic, swashplate assembly, collective, and related systems. The collective walking beam was found fractured immediately forward of its pivot point. The aft end of the walking beam remained attached to the upper swashplate, and the pivot point remained attached to the main transmission housing. Control linkages forward of the walking beam fracture were consumed by the postimpact fire.
Fractured pieces from two brackets and the lower universal housing of the lower swashplate assembly, the end of the push-pull rod assembly, and the collective walking beam were sent to the NTSB Materials Laboratory for further examination. Analysis revealed features and deformation patterns on fracture surfaces consistent with overstress separations. No indications of pre-existing cracks or fatigue cracks were observed. Darkened areas and/or rough surface texture consistent with heat damage were found on all examined components. The collective walking beam material was identified via X-ray fluorescence as ASTM A356 aluminum alloy, consistent with specifications.