ROBINSON HELICOPTER COMPANY R44 II near Mt. Baldy, CA — 2016-12-29

Probable cause

The pilot's failure to maintain main rotor speed during a low orbiting approach over a confined mountainous area. Contributing to the accident was the pilot's decision to attempt to land in an area that did not allow for a safe exit path under conditions near the limit of the helicopter’s performance capability.

NTSB narrative

The commercial pilot planned to land the helicopter at the top of a high mountain peak. Three passengers were onboard, and the helicopter was loaded just below its maximum gross weight. The enroute climb was uneventful, and after reaching the peak, the pilot performed an orbit over the landing site. While surveying his landing options, the helicopter's low rotor rpm warning horn sounded, and he corrected by lowering the collective and increasing engine power. The horn stopped, and he continued to circle the area while reviewing an engine limit manifold pressure chart and determining that he had enough engine power available to proceed. Hikers were close to his intended landing area, so he initiated an approach with a tailwind toward the lower face of a ridgeline with the intention of turning back to land into the wind. As he approached the landing spot, the low rotor rpm horn sounded again, and he lowered the collective. The helicopter descended rapidly, and due to terrain, there was no escape path, so he warned the passengers to brace for impact. The helicopter landed hard and sustained substantial damage. The helicopter was operating at the upper limit of its performance capabilities at the reported gross weight and calculated density altitude. Performance charts indicated that the helicopter would not have been able to hover at that altitude, and as such, a successful landing, while not impossible, would have been challenging. The activation of the warning horn during the initial orbit would have been another indication to the pilot that there was limited engine power available for landing. The pilot reported no preimpact mechanical malfunctions or failures with the airframe or engine that would have precluded normal operation, and the accident is consistent with the pilot's failure to maintain rotor rpm while operating near the helicopter's performance limits.

Analysis

Primary failure mode

Loss of control

First missed decision gate

Pilot could have aborted the approach when low rotor RPM warning sounded.

NTSB coding

• Loss of lift · Approach
• Decision Making / Judgment

Evidence available

• ADS-B / radar
• Photos
• 8 docket documents

Docket documents8

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Pilot Statementinterview
• Maintenance Logbook Excerptsother
• N324RS Current Weight and Balanceother
• Pilot's Operating Handbook Excerptsother
• Weather Research and Forecasting Computer Model Air Soundingother
• Factual Report Imagesphotos
• Approximate Flight Track Data - Provided by Harris Corporationradar

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