What happened
During a training flight at Hare Field, Ontario, a Schweizer 2CO (300C) helicopter, registration C-GGUV, was performing practice autorotations. The flight, involving an instructor and a student pilot, was intended to review maneuvers in preparation for an upcoming flight test. After completing several successful straight-in autorotations, the student pilot initiated a 360-degree autorotation from an altitude of approximately 800 feet.
As the maneuver progressed, the aircraft's airspeed dropped significantly, and the rate of descent increased sharply. The instructor took control at roughly 200 feet altitude, noting an airspeed of 25 knots and a rotor speed of 400 rpm. Attempting to recover, the instructor lowered the nose to regain speed and then raised it to flare for landing, but did not apply power. The helicopter struck the turf with a nose-up attitude, causing the skids to spread and the aircraft to roll forward and land inverted. The aircraft sustained substantial damage, though both pilots escaped with only minor injuries.
The investigation
The investigation examined the flight training procedures, the student's experience, and the instructor's decision-making. It was noted that the student had previously practiced these maneuvers at much higher altitudes, whereas this specific exercise began at a lower height. The investigation also reviewed the adequacy of the pre-flight briefing, which was found to be abbreviated and lacked specific discussions regarding contingency planning or error correction.
Furthermore, investigators analyzed the technical guidance provided in various Canadian aviation manuals, including the Flight Training Manual and the Flight Instructor Guide. They specifically looked at the use of the height-velocity chart and the instructions regarding the "shaded area" of the aircraft's performance envelope.
Findings
- The primary cause of the accident was the instructor's decision to continue the autorotation after the aircraft had entered a state where a safe recovery was no longer assured.
- The student pilot failed to recognize the developing unsafe condition due to a lack of experience and a reliance on the instructor to intervene.
- The 360-degree autorotation was initiated at an altitude too low to provide an adequate margin for error.
- Ambiguous guidance in official reference materials regarding safe entry heights and the significance of the height-velocity chart contributed to the risk.
- A lack of detailed briefing meant the instructor and student held different expectations regarding altitude and maneuver execution.
- The instructor's uncertainty regarding the risks of operating within the height-velocity chart's shaded area led to an inappropriate attempt at a power recovery.