What happened
On 5 July 2011, an Agusta A109C, registration N109TK, was conducting a private flight from London Battersea. While cruising at 750 feet altitude and a speed of 150 knots along route H10, the aircraft experienced a bird strike. A Herring Gull collided with the left windshield, causing the acrylic material to shatter into multiple sections.
The impact caused the commander, who was operating the aircraft from the left seat, to be struck by fragments of the windshield and bird remains. The co-pilot, seated in the right seat, took control of the aircraft and declared a mayday. Following the incident, the co-pilot performed an emergency landing in a field near Kew Bridge. The commander sustained minor cuts and grazes but did not require medical treatment.
The investigation
Investigators examined the damage to the aircraft and the nature of the windshield. The upper portion of the left windshield, constructed of 3.81 mm thick acrylic, had broken into several large and small pieces. Evidence of blood spatter on the left door post suggested that while the commander was struck by fragments, the bird itself likely hit the door post after penetrating the windshield. The remains of the Herring Gull were recovered from inside the cabin.
The investigation also reviewed the regulatory requirements for the aircraft type. The Agusta A109C was certified under US Federal Aviation Administration (FAA) Regulation Part 27. Under these regulations, windshields are only required to be made of material that does not break into dangerous fragments; there is no specific requirement for the windshield to withstand bird strikes. This differs from Part 29 certification, which requires larger rotorcraft to be capable of safe landing after a 1.0 kg bird impact.
Findings
- The incident was caused by a Herring Gull striking the left windshield at a relative speed of approximately 150 knots.
- The aircraft's acrylic windshield was not designed to withstand bird strikes.
- The commander sustained minor injuries from fragments and bird debris.
- The co-pilot successfully managed the emergency landing after the commander was incapacitated by the impact.