CEN13LA437

The flight instructor reported that, during takeoff, as the helicopter climbed through 300 feet, the private pilot started a right downwind turn. At that time, they heard a loud sound and ricocheting metal directly behind their heads, and the collective control was unresponsive. The flight instructor immediately took control of the helicopter and prepared to land. He lowered the collective to start a descent; however, the collective control was still unresponsive. He then chose to set the helicopter up for a long, shallow approach over an open field to the helipad. During a turn at 60 knots indicated airspeed, the helicopter began to oscillate vertically. The flight instructor heard popping sounds, and the oscillations increased. The main rotor rpm began to decrease, and the flight instructor lowered the collective and increased the throttle; however, the main rotor rpm continued to decrease. The helicopter started to shake violently, and the flight instructor observed that the blade pitch was very high. The shaking increased, and the flight instructor could no longer control the helicopter. A few seconds later, the helicopter impacted the ground. 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 assembly, and the pivot point remained attached to the main transmission housing. The collective control linkages forward of the walking beam fracture were consumed by the postimpact fire. Examination of the 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 revealed features and deformation patterns on the 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 observed on all of the components' surfaces. The reason for the loss of collective control could not be determined due to extensive fire damage.

On July 26, 2013, about 1230 central daylight time, an Enstrom F-28A helicopter, N287Q, was substantially damaged when it impacted the ground near Danbury, Texas. A postimpact fire ensued. The flight instructor was seriously injured and the private pilot had minor injuries. The helicopter was registered to and operated by Salaika Aviation LLC., under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed for the flight, which operated without a flight plan. The flight was originating at the time of the accident.According to the written statement submitted by the flight instructor, he had flown with two other students prior to the accident flight. Those flights were uneventful and no mechanical anomalies were encountered. The flight instructor refueled the helicopter and confirmed that 25 gallons of fuel were on board. Immediately following the warm up and pre-takeoff checks, the private pilot hover taxied the helicopter to runway 24 and departed. As the helicopter was climbing through 200 feet, the private pilot initiated a turn to the crosswind. As the helicopter climbed through 300 feet, the private pilot started a right turn to the downwind, at which time a loud sound, described as a "gun shot", and ricocheting metal was heard by the instructor and private pilot. This sound was heard directly behind their heads and was accompanied by an unresponsive collective control. The flight instructor immediately took control of the helicopter and prepared to land immediately. He lowered the collective to start a descent; however, there was no response from the flight control input. The flight instructor elaborated that the collective "moved freely in [his] hand with no resistance or effect on the helicopter." He then elected to set the helicopter up for a long, shallow approach to the helipad, over an open field. During the turn at 60 knots indicated airspeed, the helicopter began to oscillate vertically. The flight instructor heard popping sounds, and the oscillations increased. The main rotor rpms began to decrease and the flight instructor lowered the collective and increased the throttle; however, this had no effect and the main rotor rpm continued to decrease. The helicopter started to shake violently and the flight instructor observed the blade pitch was very high. The shaking increased and the flight instructor could no longer control the helicopter. A few seconds later, the helicopter impacted the ground. The helicopter sustained substantial damage during the impact and the postimpact fire. Investigators with the National Transportation Safety Board (NTSB) examined the fractured and burnt remains of the collective push-pull rod assembly, cyclic, swashplate assembly, collective, and other related systems. The collective walking beam was found to have fractured immediately forward of its pivot point. The aft end of the walking beam remained attached to the upper swashplateassembly and the pivot point remained attached to the main transmission housing. The collective control linkages forward of the walking beam fracture were consumed by the post-impact fire. Fractured pieces from two brackets and the lower universal housing of the lower swashplate assembly, the end of the push-pull rod assembly, control cyclic, and collective pitch, and the collective walking beam were sent to the NTSB Material Laboratory for further examination. The examinations revealed features and deformation patterns on the fracture surfaces that were 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 observed on the surfaces of all of the components. The collective walking beam was analyzed using a Thermo Scientific Niton XL3t-980 x-ray fluorescence (XRF) alloy analyzer. The alloy analyzer identified the material as ASTM A356 aluminum alloy, which is consistent with the alloy specified for the collective walking beam.