Enstrom F-28A N287Q accident near Danbury, Texas

Probable cause

The loss of collective control for reasons that could not be determined due to extensive fire damage.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for CEN13LA437 for the full record.