Accident Overview
On March 11, 2011, at approximately 1450 Pacific standard time, a Robinson R-22 Beta II helicopter, registered N8360T, rolled onto its side after one of its skids contacted the terrain during an instructional flight at North Las Vegas Airport, North Las Vegas, Nevada. The helicopter was owned by Tamiry Aviation LLC and operated by 702 Helicopters. The certified flight instructor and his student were not injured, but the aircraft sustained substantial damage. The local instructional flight under 14 Code of Federal Regulations Part 91 had begun about 50 minutes prior and was conducted in visual meteorological conditions. No flight plan had been filed.
Pre-Flight and Initial Phase
According to the instructor, the primary objective was to teach the student, who had accumulated less than 2 hours of helicopter instructional flight time, how to perform a stationary hover. During the startup and pre-takeoff checklist, the instructor observed a dramatic drop in engine rpm when checking the right magneto, whereas the left magneto showed only a four or five percent drop. He rechecked the right magneto; the rpm dropped about six or seven percent within two seconds, then continued to decrease to a total drop of about fifteen percent in four or five seconds. Although concerned that the rpm continued dropping past seven percent, the instructor noted it technically met the two-second limit and decided to continue the flight.
In-Flight Performance Issues
During the flight, the instructor noticed the helicopter required an unusually high power setting to maintain a hover of 2 to 3 feet above ground level (agl). He commented to his student that the difficulty might be due to the helicopter being "very underpowered." About 30 minutes into the flight, due to perceived underperformance, the instructor landed to perform another magneto check. The right magneto check produced similar results: a drop of six to seven percent within two seconds, followed by a continuing total drop of about fifteen percent in four to five seconds. Afterward, the instructor ran the engine at a lean fuel setting for about two minutes to burn off possible carbon or lead deposits. He then lifted the helicopter back into a hover but determined that nothing had changed, and it still required about maximum continuous power to hold a 3-foot hover.
Accident Sequence
Despite the performance concerns, the instructor decided to continue the instructional flight and turned controls over to the student. The student established a hover at about 3 feet agl and was hovering fairly well, according to the instructor. Suddenly, the helicopter began to descend. The student reacted by inputting right cyclic, causing the right skid to contact the ground with the helicopter tilting right. The instructor took over, adding left cyclic and up collective, but could not prevent the helicopter from rolling onto its side.
Post-Accident Examination
After the accident, the magnetos were bench tested and disassembled with no negative findings; magneto-to-engine timing was correct for both magnetos. Both magnetos had undergone their repetitive 500-hour inspection/overhaul less than 45 days prior. The leads showed no frayed shielding, shorting, unusual wear, contamination, cracked insulators, or other anomalies. The air induction system was inspected with no issues. Except for some roughness of the paint on the underside of the main rotor blade tips (noticed by the instructor before the flight), no component anomaly was observed that would have contributed to a reduction in performance.
Instructor's Remarks
In a postaccident interview, the instructor mentioned receiving a text message from another instructor the day before, who noticed a brief performance reduction during a 30-minute flight. He felt it might have been a magneto or fouled-plug issue. Reflecting on his own flight, the instructor said he had no good reason for not discontinuing after the second magneto check. He was uncomfortable with the high power required and difficulty maintaining hover height, but did not take control and return to the ramp. He speculated he may have continued because he felt capable of fixing hover problems, as he had done many times before. He later admitted that continuing the hovering instructional flight with a low-time student when the helicopter might not be performing at its normal potential was not a good decision, and that returning to the ramp after the second magneto check would have been wise.
The helicopter had flown 6.4 hours since the flight referenced in the text message.