History of the Flight
The helicopter departed from London Battersea heliport and was transiting along helicopter route H10 at 750 ft agl and 150 kt. A bird struck and shattered the left windshield. The commander, flying from the left seat, was struck by pieces of windshield and parts of the bird. The co-pilot, in the right seat, took control, declared a mayday, and made an emergency landing in a field near Kew Bridge. The commander sustained minor cuts and grazes and did not require medical attention.
Damage to the Helicopter
The upper portion of the left windshield, made of acrylic, shattered into multiple sections. The largest piece measured about 30 cm by 45 cm, several were about 15 cm by 15 cm, and many were smaller. None broke into sharp fragments. The windshield had a thickness of 3.81 mm ± 0.5 mm (part number 109-0310-27-3). Blood spatter on the left door post indicated the bird likely struck the post after shattering the windshield. The bird, mostly intact, was found inside and identified as a Herring Gull, with typical weight 690 to 1,495 g, classified as 'High' on the Hazard Probability list. Several circuit breakers and switches were broken off; some switches moved to the off position.
Bird Strike Resistance Requirements
The Agusta A109C was certified to US FAR Part 27 in 1989. Part 27 requires only that windshields be made of material that will not break into dangerous fragments, with no birdstrike resistance requirement. EASA CS-27 has the same requirement. Rotorcraft over 7,000 lb or with more than nine seats are certified to Part 29, which includes birdstrike resistance: safe landing capability after impact with a 1.0 kg bird at the lower of VNE or VH up to 8,000 ft.
Previous Incidents and Recommendations
The manufacturer was aware of three previous A109 bird strikes: one in Florida in May 2009 (A109E N911UF) where a duck shattered the windshield, causing pilot injuries; one in October 2006 in the USA; and one in Mexico in November 2009. In November 2010, the NTSB recommended to the FAA that Part 27 helicopters be required to have birdstrike-resistant windshields, citing a Sikorsky S-76C accident with eight fatalities. The FAA responded in January 2011 that they were reviewing databases. EASA also studied the issue and recommended a 2 lb/1 kg birdstrike capability for CS-27 helicopters, which was added to the rulemaking programme.