A flight instructor’s decision to attempt a challenging maneuver without adequate power was likely responsible for the rough landing of a commercial helicopter in Kona on June 29, according to the National Transportation Safety Board.

As noted in a probable cause report released on Sept. 30, the instructor and a student pilot were practicing “pinnacle” landings — landings on mountainous areas with steep drop-offs on all sides — when they approached a landing site about 8,000 feet above sea level.

The 26-year-old flight instructor told investigators that as the Robinson R22 Beta helicopter came within 5 to 6 feet of the ground, “the rotor rpm began to droop and we started to descend.”

The helicopter continued to descend despite the instructor’s attempt to increase airspeed. It skidded across the ground and rolled over onto its side, causing substantial damage to the fuselage and tail boom.

Neither the instructor nor the student were seriously injured.

The NTSB determined that the probable cause of the incident was “the flight instructor’s decision to conduct a high-altitude pinnacle landing without adequate power, which resulted in the helicopter impacting terrain during the approach.”

The report cited the air density at the landing site — which was higher than what the instructor reported for the area — as a contributing factor.