Accident Details
On 5 May 2017 at 0830 UTC, an Airbus Helicopters AS350 B3e Ecureuil, registration G-MATH, was involved in an accident during a training flight at Wycombe Air Park, Buckinghamshire. The helicopter was conducting a revision flight for type conversion training, with an instructor in the left seat, a pilot under training in the right seat, and another pilot under training as a passenger in the rear. The flight was operated under an Approved Training Organisation (ATO) based at the airfield.
History of the Flight
The helicopter departed at 0805 hrs and first completed uneventful exercises including autorotations and hover work. After returning, the instructor positioned the helicopter for a base leg approach to a grass area north of Runway 06 to begin hydraulic failure training. The instructor selected the ACCU TST switch on and then off per the flight manual procedure to simulate a hydraulic failure. The right-seat pilot then selected the HYD CUT OFF switch to depressurise the system and began a flat approach for a run-on landing.
Accident Sequence
During the first approach, the instructor was dissatisfied with the pilot's yaw and speed control, took control, and initiated a hydraulics-off go-around. A left-hand circuit was flown with up to 32° angle of bank (AOB) to reposition for a second attempt. The instructor handed control back for the second approach, but again took control late in the approach and initiated another go-around, followed by a left turn. On this occasion, the AOB increased beyond 48°. Recorded image data showed the instructor changing his grip and leaning right as if to apply more right cyclic force. The AOB stabilised briefly, then the helicopter rolled further left, descended rapidly, and struck the ground on its left side. The aircraft came to rest on a heading of 019°(M) within the airfield boundary.
Aftermath and Investigation
All three occupants were seriously injured. The right-seat pilot died weeks later from injuries sustained in the accident. The instructor and rear passenger survived. No technical issues were identified, and a definitive reason why the instructor was unable to roll the helicopter back to a level attitude could not be determined. The investigation concluded that clearer instructions in the AS350 flight manual for hydraulics-off flight would help prevent similar accidents. The manufacturer amended the flight manual to limit AOB to 30° during hydraulics-off flight, included warnings against low-speed manoeuvres, and produced a safety video.
Aircraft Information
G-MATH was a 2016 AS350 B3e with a single Turbomeca Arriel 2D engine. It had six seats and a single hydraulic system. Normal flight control with hydraulics on uses powered actuators; with hydraulics off, controls operate mechanically with higher forces. The manufacturer's recommended safe airspeed range for hydraulics-off flight is 40 to 60 kt. The helicopter was also fitted with a HeliSAS autopilot system. The accident site showed the helicopter struck the ground with little forward speed, main rotor blades hitting first at near 90° left bank while powered.