What happened
On 7 November 2003, an Eurocopter EC 120B, registration EI-IZO, was performing a stationary hover over the apron at Swansea Airport. The aircraft was operating in connection with the Wales Rally Great Britain 2003, carrying a pilot and four passengers.
While the helicopter was hovering, the wind was gusting between 15 and 20 knots from the right and slightly behind the aircraft. Suddenly, the helicopter yawed to the left and experienced a significant nose-down pitch. The pilot attempted to recover by applying full aft cyclic control, but the control reached its physical limit, and the aircraft could not be leveled. The nose and the right skid made contact with the paved surface, followed immediately by the main rotor blades.
The impact caused the helicopter to roll onto its right side and slide across the apron. During the slide, the rotor blades struck the tail boom, severing the fenestron, and the aircraft eventually came to rest against a small airport tractor. Despite the substantial damage to the aircraft, all five persons on board escaped without injury.
The investigation
Investigators examined the aircraft's weight and balance, the flight control systems, and the meteorological conditions. The investigation established that the aircraft's centre of gravity (CG) was approximately 5mm forward of the forward limit. While this was a marginal deviation, it was noted that the pilot had not performed a specific weight and balance calculation for the current load.
Regarding the flight controls, the investigation found that the left crew seat was locked in the fully forward position. While full aft cyclic authority was available during testing, it was noted that the physical presence of a passenger in the left seat could potentially restrict lateral cyclic movement.
Findings
- The primary cause of the accident was the uncommanded pitch-down caused by the effects of gusting winds acting on the helicopter.
- The aircraft was operating in gusty, varying wind conditions that destabilised the hover.
- The forward CG position and the aircraft's weight acted as aggravating factors, reducing the available control authority needed to counter the pitch rate.
- The pilot's inability to prevent the nose-down attitude was due to the cyclic control reaching its aft limit.
Safety action
- It is recommended that Eurocopter highlight the risks to EC 120 operators regarding correct loading and the adverse effects of gusting tailwinds on helicopters with a forward CG.
- It is recommended that Eurocopter update the Approved Flight Manual to include information regarding potential restrictions in cyclic control movement caused by the physical positioning of crew members in dual-control configurations.