What happened
On September 12, 2022, a Grumman American AA-5B Tiger, registration OO-XXX (not specified, but Belgian-registered), was performing a non-commercial cross-country flight from Grimbergen to Zwartberg. While cruising at 1,500 ft AMSL in class G airspace near Itegem, the aircraft struck an 800g herring gull.
The impact was severe enough to shatter the cockpit windshield, allowing the bird to enter the cabin and land on the rear seat. The collision also struck the pilot's head, knocking off their headset and smearing their goggles. Despite the intense wind noise and propeller wash making communication difficult—leading air traffic services to initially misinterpret a PAN PAN declaration as a report of fire—the pilot successfully navigated the aircraft back to the aerodrome of Grimbergen. The aircraft sustained substantial damage, though no injuries were reported.
The investigation
AAIU(Be) conducted a limited-scope investigation focusing on the immediate circumstances of the strike. Investigators examined the aircraft's structural damage, noting that while the windshield was breached, the propeller remained undamaged. The investigation also consulted the Research Institute Nature and Forest of the Flemish government to identify the species and assess local bird activity.
Furthermore, the investigation reviewed certification standards for small aircraft. It was noted that under current CS-23 regulations, aircraft with fewer than 10 seats are not required to have windshields capable of withstanding an impact from a bird of this mass at the aircraft's speed. The investigators also analyzed the pilot's equipment, noting the importance of having spare corrective eyewear accessible in the cockpit.
Findings
- The primary cause of the incident was the impact of an 800g gull at an airspeed of 110 KIAS.
- The aircraft's certification standards do not require the windshield to withstand a strike by a bird of this weight.
- The pilot's ability to declare a PAN PAN and return to the departure aerodrome was a positive factor in preventing further escalation.
- High-altitude flight by gulls is possible via thermals, even in areas not near primary breeding colonies.
- Effective communication with ATC was hindered by the extreme noise levels inside the cockpit following the windshield breach.