Accident involving Puma XW211 on 5 Jul 2011

On 5 July 2011, a Royal Air Force Puma HC1 (serial number XW211) from RAF Benson was conducting a transit flight. During a scheduled stop at Middle Wallop airfield for a refuel and crew change, the crew noticed a discrepancy in the hydraulic fluid levels. To diagnose the potential leak, the crew opened the Main Rotor Gearbox (MRGB) cowling—the large protective fairing atop the fuselage. After a telephone consultation with engineering personnel at their home base, the crew believed the issue was manageable and prepared to return to RAF Benson.

Approximately three minutes after taking off from Middle Wallop, the MRGB cowling became unsecured and was ripped away by the aerodynamic forces. The detached cowling struck both the Main Rotor Blades and, more critically, the Tail Rotor Blades. The impact caused severe damage to the tail rotor drive and control systems, leading to an immediate and violent loss of directional control. The crew, facing a rapidly deteriorating situation, managed to perform an emergency "autorotative" landing in a field southeast of Andover, near the A303.

The Service Inquiry (SI) identified the "Causal Factor" as the failure to properly secure the MRGB cowling before flight. The investigation found that the cowling's fasteners had not been fully engaged after the maintenance check. A "Contributory Factor" was the crew's operational pressure and the informal nature of the "telephone engineering advice" received, which did not sufficiently emphasise the criticality of the cowling security checks. Furthermore, the inquiry noted that the Puma HC1's cowling design did not have a clear visual "unlocked" indicator, making it difficult for the crew to spot the error during a standard pre-flight walk-around.

The airframe was written off due to the severity of the impact and the structural damage caused by the rotor strikes. This incident highlighted the dangers of "human error" in seemingly routine maintenance tasks and led to a redesign of the checklist procedures for Puma aircrew, ensuring that any opening of major cowlings away from a main base required a more formalised inspection process.