LAX00LA276 · Schweizer 269C

The helicopter sustained substantial damage when it descended into a rough rock-strewn field while attempting to hover. The density altitude at the 2,200-foot msl accident site would have been about 5,000 feet. The normally aspirated engine's critical altitude is 4,000 feet and the Rotorcraft Flight Manual shows that the maximum available manifold pressure at that altitude is 24.8 inches. The pilot said that he chose a spot suitable to hover for a closer look at items of interest on the ground. He made a shallow approach to the spot and loaded the rotor blades as the helicopter slowed; when the helicopter reached a hover, the manifold pressure was at 25 inches. The next thing the pilot realized was that the rotor rpm was near the bottom of the green arc and the helicopter was settling toward the ground. The pilot reduced the collective a small amount and rolled the throttle full on; however, the helicopter began settling faster. The pilot used collective in an attempt to cushion the landing but the skids touched down hard on a large rock, bending the skids and fuselage structure and damaging the tail boom. The pilot reported that after the helicopter came to rest when the collective was lowered all the way the rotor rpm recovered. The pilot then completed a normal engine cool down and shutdown procedure. The pilot said that when the rpm first decayed and the helicopter began to settle, he initially thought about trying to fly forward out of the descent. Large rocks, high brush, and rising terrain were directly in front, and he feared that the damage and injury potential there was much worse if the helicopter had continued to settle. Review of the performance charts in the Helicopter Flight Manual revealed that the reported temperature and pressure altitude of the accident site for the estimated weight of the helicopter was very near the limit for an out of ground effect hover.

Verbatim NTSB analysis and probable cause from the NTSB dataset