Summary
On 16 July 2006 at 1730 UTC, a Bell 206B Jet Ranger (G-NEWS) sustained major damage during a training flight at Cambridge Airfield, Cambridgeshire. The aircraft, fitted with a high-skid landing gear, was completing an Engine Off Landing (EOL) exercise when the touchdown was slower and heavier than normal. The helicopter bounced approximately 3 to 4 feet, and on the second touchdown, the tail strike protector struck the ground, causing the tail rotor gearbox to detach and the main rotor blades to contact the vertical stabilizer. Both occupants, an instructor and a student, were uninjured.
History of the Flight
The student pilot was undergoing a 5-hour type conversion on the Bell 206B Jet Ranger, with training shared between two instructors. All training had been conducted in the same helicopter. On the day of the accident, the weather was good with a light surface wind from 060° at 7 to 9 kt, CAVOK conditions, and a surface temperature of 29°C. The instructor planned two flights: the first was instructional, and the second was a revision prior to the Licence Skills Test. At the end of the first flight, the student performed two Practice Force Landings and two EOLs unassisted to a satisfactory standard. The second flight included the final exercise of an EOL.
Flight Details
The aircraft was positioned for the EOL onto a grass surface in the south helicopter training area, on a heading of 280°, at a height of 700 ft and an indicated airspeed of 90 kt. The instructor initiated the exercise, the student entered autorotation, and the instructor closed the throttle to idle. The student turned into the wind, and at about 300 ft, the instructor confirmed it was safe to continue. The height and approach angle ensured the EOL area would be achieved, with an indicated airspeed of approximately 65 mph and rotor rpm at about 100%. The student commenced the flare at the normal height, reducing the rate of descent. As the aircraft decelerated, the instructor called for the student to level the aircraft, which he did at a skid height of about 8 ft with very little forward speed. As the aircraft began to descend, the student raised the collective pitch control lever to cushion the landing. The instructor, monitoring the collective, thought the rate of application appeared normal. The aircraft touched down heavily in a level attitude but bounced back to a height of about 3–4 ft. The instructor took control as the 'LOW RRPM' warning horn sounded. He attempted to cushion the second touchdown, managing to control the aircraft to a skid height of approximately 2 ft in a stable attitude but had no further control below that height as the aircraft dropped. On contact with the grass, the aircraft shuddered for about two seconds then settled. The instructor shut down the engine, applied the rotor brake, notified ATC, switched off the electrical system, and both occupants vacated through normal exits. The airfield Rescue and Fire Fighting Service attended within two minutes.
Engineering Findings
From discussions with the repair agency, on the second touchdown, the tail strike protector struck the ground with sufficient force to bend the tail pylon upwards at a point approximately 12 to 14 inches aft of the pylon-to-fuselage attachment. The tail rotor gearbox detached, and the main rotor blades impacted the vertical stabilizer. The main rotor gearbox mounting plate showed evidence of forward movement, and the front left cross tube exhibited signs of a heavy impact.
Analysis
The EOL exercise had been fully briefed and demonstrated earlier, and the student had successfully completed it on previous flights. The EOL was entered at a safe height, allowing adequate time to stabilise and position the aircraft. Up to the point of raising the collective lever to cushion touchdown, the EOL appeared normal. It is possible that following the heavy touchdown, the student continued to raise the collective, which may have contributed to the height of the bounce. With high collective pitch applied, the rotor rpm decayed rapidly, limiting the effectiveness of the flight controls. The tail-first landing and contact of the tail rotor blade with the ground or airframe likely caused the tail rotor gearbox to separate. The high-skid landing gear was not considered a factor. The instructor considered two possibilities: the student may have made an inadequate collective input to reduce the sink rate, though the instructor believed the collective movement was appropriate and a normal touchdown should have followed; alternatively, they may have encountered windshear from the light and variable surface wind combined with the high ambient temperature.