Maintenance Test Flight Ends in Crash of Robinson R44 II

Casualties unknown • Cambridge, Ontario, CA

A maintenance check flight in Ontario resulted in the destruction of a Robinson R44 II after the rotor RPM decayed during an unauthorized autorotation procedure.

What happened

On 20 January 2007, a Robinson R44 II helicopter, registration C-FGTN, was performing maintenance check flights near the Kitchener/Waterloo Regional Airport. The flight was intended to track the main rotor blades and verify rotor revolutions per minute (RPM) during an autorotation. Following a recent replacement of the main rotor blades, an aircraft maintenance engineer (AME) and the pilot were conducting these tests to ensure proper blade tracking and pitch link adjustments.

During the descent into autorotation, the aircraft's rotor RPM dropped significantly. The engineer, who had been focused on observing the rotor blades, noticed the engine/rotor RPM gauge had fallen to approximately 80 per cent and that the aircraft was in a nose-down attitude. The helicopter continued its descent and struck a snow-covered field. The impact caused the aircraft to be destroyed, and the seat belt attachments failed, resulting in two serious injuries as both occupants were ejected from the cockpit.

The investigation

Investigators examined the aircraft's maintenance history and the procedures used during the flight. It was established that the aircraft had recently undergone blade replacements. The investigation found that the procedure of tracking blades during an autorotation was not a recognized method in the manufacturer's maintenance manual. Furthermore, the aircraft's gross weight at the time of the flight was 2279 pounds, which exceeded the manufacturer's limit of 1900 pounds for conducting autorotational RPM checks.

Findings

  • The maintenance engineer attempted to track the main rotor blades during an autorotation, a procedure not supported by the manufacturer's manual.
  • The gross weight of the aircraft exceeded the maximum allowable limit for performing the specified RPM check.
  • The pilot's ability to monitor essential aircraft performance was likely compromised by the attempt to combine blade tracking with the autorotation maneuver.
  • During the maneuver, the rotor RPM decayed to roughly 80 per cent, leaving insufficient altitude and time to recover the descent before impact.

Probable cause

The accident was caused by the use of an unauthorized maintenance procedure involving blade tracking during an autorotation, combined with an aircraft weight that exceeded the manufacturer's limits for such a test, leading to a critical decay in rotor RPM.

Frequently asked questions

What happened in the 2007-02-02 Robinson R44 II, C-FGTN accident near Cambridge, Ontario, CA?

A maintenance check flight in Ontario resulted in the destruction of a Robinson R44 II after the rotor RPM decayed during an unauthorized autorotation procedure.

What aircraft was involved and where did it happen?

The accident on 2007-02-02 involved a Robinson R44 II, C-FGTN, operated by The Helicopter Company Inc., at Cambridge, Ontario, CA.

What was the probable cause of the accident?

The accident was caused by the use of an unauthorized maintenance procedure involving blade tracking during an autorotation, combined with an aircraft weight that exceeded the manufacturer's limits for such a test, leading to a critical decay in rotor RPM.

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