Accident Details
On a day visual flight rules training flight, a Robinson R22 Beta helicopter, serial number 2110, was conducting autorotation practice 20 nautical miles north of Toronto/Buttonville Municipal Airport, Ontario. After 45 minutes of practicing autorotations, the student pilot was flying the helicopter back to the airport at 1700 feet above ground level when the instructor simulated an engine failure. The student selected a field and executed a forced approach. At 40 feet agl, the student began to flare the helicopter by moving the cyclic aft. As the descent continued, the helicopter approached tall trees at the end of the field. The student pulled up hard on the collective, and the instructor opened the throttle to initiate a recovery. However, engine rotor rpm was low, and the engine did not respond. The descent could not be arrested, and the aircraft struck the ground. The left skid tip dug into the semi-frozen ground, and the helicopter pivoted forward onto its right side. Both pilots evacuated through the left door. Neither pilot was injured, but the helicopter was substantially damaged. The accident occurred at 1040 eastern daylight time.
Aircraft Information
The Robinson R22 Beta helicopter, manufactured in 1992, had accumulated 4699 hours. It was equipped for visual flight rules operations and used mainly as a primary rotary-wing trainer. Records indicate the helicopter was equipped, maintained, and certified in accordance with existing regulations and approved procedures. No known defects existed before the flight. The aircraft's weight and centre of gravity were within approved limits.
Pilot Information
The instructor pilot held a valid Canadian Airline Transport Pilot Helicopter licence on multiple helicopter types, a Class 2 instructor rating, and a Group 4 instrument rating. He had over 8950 hours total rotary wing time, with approximately 1800 hours on the Robinson R22 Beta. In the previous 90 days, he flew 90 hours, including 35 hours in the previous 30 days.
The student pilot held a valid Canadian Student Pilot Helicopter permit and had accumulated 20 hours of flying time, all on the Robinson R22 Beta, all within the previous 90 days, including 10 hours in the previous 30 days.
Weather
At 1000 eastern daylight time, weather at Toronto/Buttonville Municipal Airport was: sky clear, visibility greater than 12 statute miles, temperature 8°C, dew point −3°C, wind 350° true at 6 knots, altimeter 30.38 inches of mercury.
Autorotation Procedure Description
According to Transport Canada's Helicopter Flight Training Manual, an autorotation is a condition where the rotor is driven by aerodynamic forces with no power from the engine. During autorotation, the helicopter remains fully manoeuvrable in descending flight. The Robinson R22 Pilot Operating Handbook recommends: lower collective immediately, establish a steady glide at 65 KIAS, adjust collective to keep rotor rpm in the green arc, select a landing area, at 40 feet agl begin cyclic flare to reduce rate of descent and airspeed, and at 8 feet agl apply forward cyclic and raise collective before touchdown. The main-rotor blade system is considered a low-inertia rotor system, meaning the rotor depletes stored energy quickly, which can lead to rotor rpm decay and aerodynamic stall. Robinson Safety Notice SN-24 warns that low rotor rpm can cause fatal rotor stall.
Accident Sequence
The student selected a field with an upslope from 4° to 6° and tall trees at the eastern end. The instructor saw the field was inappropriate but judged it safe to continue, planning to have the student perform a power-on recovery and discuss field selection. As the helicopter descended through 40 feet agl, the student flared and, seeing approaching trees, aggressively pulled up on the collective and aft on the cyclic. The low-rotor-rpm warning horn sounded. The instructor opened the throttle, but the engine did not respond. At approximately 30 feet agl, rotor rpm fell below 50% and continued dropping.
The helicopter contacted the ground in a level attitude at about 10 knots forward speed. The emergency locator transmitter activated. Ground scarring showed the initial heading was approximately 040° magnetic. The wreckage trail was 40 m long on a heading of 320° magnetic. The tail boom was severed by the retreating main-rotor blade and thrown 25 m north. The advancing main-rotor blade struck the ground and was bent to −85°. Neither main-rotor blade separated. The cockpit was structurally intact, but windshields and right door window broke. Examination showed the main rotor and tail rotor were in a low-energy state at impact. Drive train and flight control continuity were confirmed. No pre-impact airframe failure or system malfunction was found.
Findings
Findings as to causes and contributing factors: During the practice autorotation, the helicopter's main-rotor rpm was allowed to drop below safe limits, leading to an aerodynamic stall of the main-rotor blades. The instructor pilot allowed the student pilot to conduct the practice forced approach and autorotation into an inappropriate field.
Findings as to risk: Before the exercise, the instructor placed inadequate emphasis on the dangers of low main-rotor rpm and rotor-blade stalls.