History of the Flight
The pilot and one passenger were returning from Kotrijk, Belgium, to a private landing site near Oxford. While passing through the Stansted control zone, the helicopter's autotrim in the Automatic Flight System disengaged, and the helicopter pitched nose-down. The pilot, interpreting this as a double engine failure, entered autorotation. During the landing flare, the tail struck the ground first, severing the fenestron drive. The helicopter subsequently rolled onto its right side, sustaining extensive damage. The occupants escaped without injuries.
Helicopter Information
The aircraft was a Eurocopter EC135 T2, registration G-IWRC, powered by two Turbomeca Arrius 2B2 turboshaft engines. It was equipped with a Central Panel Display System (CPDS), Auto Flight System (AFS), and a high skid assembly. The AFS included a three-axis autopilot with Stability Augmentation System (SAS) and pitch damper. The pilot had 2,500 hours total flight experience, with 450 hours on type.
Events Leading to the Landing
At 1309 hrs, the helicopter was at 1,000 ft near Billericay. The pilot obtained clearance to cross the Stansted control zone and climbed to 1,500 ft using ALT ACQUIRE mode. While consulting a flight guide, he heard and felt a dull thud from above and behind, similar to a bird strike. He noticed the helicopter pitching nose-down. His wife expressed alarm. The pilot took the controls and entered autorotation. He checked instruments and recalled one needle on the triple tachometer pointing up, one normal, and one down. He made an emergency call to Essex Radar, who provided bearing and distance to North Weald. Realizing he could not reach the airfield, he selected a field for landing.
Impact and Damage
The helicopter touched down tail first on a track with a heading of approximately 345°. The tail dragged for about 3.5 m before both skids touched down. The helicopter ran for another 10 m before rolling onto its right side. The tail boom broke just forward of the horizontal stabilizer, and all four main rotor blades failed near the roots. The fenestron fan made contact with the duct, and two blades broke off. The damage was consistent with a heavy tail strike. Engines were undamaged and rotated freely; air intakes were covered in vegetation.
Warnings and Systems
The Warning Unit stores the last 31 warnings. During the accident flight, the AP A TRIM warning would have illuminated and a gong sounded if the autotrim disengaged. The pilot did not recall visual or aural warnings. The SAS DCPL switch, if operated, disengages autopilot, pitch damper, and SAS, which can cause uncommanded control inputs. The pilot's assessment of a double engine failure led to the autorotation.