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Open Access Publications from the University of California

Have population increases of large birds outpaced airworthiness standards for civil aircraft?


Bird-aircraft collisions (bird strikes) are an increasing safety and economic concern to the USA civil aviation industry, costing over $400 million each year. One approach to reducing risks associated with strikes is to require commercial aircraft components to meet certain standards of safe performance in the event of a bird strike. The Federal Aviation Administration has developed airworthiness standards for airframes, windshields and engines using a single 4-lb (1.82-kg) bird mass as the maximum that must be tested (with the exception of a single 8-lb bird for the empennage, 6-lb bird for certain mid-sized engines that may be developed in the future, and an 8-lb bird for certain large-intake engines on aircraft such as the Boeing 777). Because of concern within the aviation industry that populations of certain flocking bird species weighing more than 4 lbs, such as Canada geese (Branta canadensis), have increased dramatically, discussions are underway in the USA and Europe regarding the need to revise 4- and 8-lb test standards to heavier body masses or to include multiple strikes. To help clarify this issue, we surveyed the avian literature and determined that 36 and 14 of the approximately 650 bird species that nest in North America (north of Mexico) have average body masses (for at least 1 gender) greater than 4 and 8 lbs, respectively. Of the 31 species for which population trend data were available, 24 (77%) showed population increases over the past 20-40 years, 2 showed declines, and the other 5 were stable. Thirteen of the 14 species with mean body masses over 8 lbs showed population increases. At least 261 strikes with >4-lb birds caused substantial damage to civil aircraft in the USA, 1990-2001. Furthermore, multiple birds were involved in 31% of the strikes with >4-lb birds and 40% of the strikes with >8-lb birds. Therefore, we conclude that airframe, windshield, and engine standards, as well as proposals to allow high-speed (>250 knot) operations below 10,000 feet, should be reevaluated to address the threat posed by increased populations of large flocking birds. Finally, because most critical aircraft components are not designed to withstand strikes by birds greater than 4 lbs, wildlife biologists who work at airports should increase efforts to detect, remove and disperse these large birds from airport environments.

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