Robinson Helicopter R22 BETA II N8360T accident near North Las Vegas, Nevada

Probable cause

The partial loss of engine power for undetermined reasons. Contributing to the accident was the certified flight instructor's decision to continue the flight after the helicopter exhibited inadequate performance capabilities and an unresolved power production issue.

NTSB analysis

While conducting the pre-takeoff check of the right magneto, the certified flight instructor (CFI) determined that the drop in the helicopter's engine rpm remained within operational limits during the required two-second check period, but that it continued to drop significantly for a short period thereafter. A second check sequence produced the same results. Although concerned, the CFI continued the instructional flight, whereupon he determined that maneuvering the helicopter was taking considerably more power than he was accustomed to. About 30 minutes into the flight, the CFI landed the helicopter to once again check the right magneto because of the apparent lack of performance. The results showed the same excessive post-check rpm drop. After lifting the helicopter back airborne, and returning control to the student in a low hover, the helicopter suddenly descended, contacting the surface with one skid. The CFI then took control of the helicopter, but was unable to keep it from rolling onto its side. A postaccident test and disassembly inspection of the helicopter's magnetos and ignition system did not reveal a reason for the rpm drop or the reduction in performance.

Text from the NTSB. Open the NTSB docket for WPR11LA161 for the full record.