Sharing the sky with birds

The dramatic ditching two weeks ago of US Airways flight 1549 in New York’s Hudson River shows what can happen when birds and airplanes cross paths. Although relatively rare and generally not harmful to aircraft or their occupants, bird strikes do occur and have been part of the aviation scene since the beginning.

Orville Wright logged an in-flight encounter with a bird in 1905. While circling his flying field east of Dayton, Ohio, the younger Wright brother flew through a rising flock and struck one of the birds. Stunned or dead, it lay accusingly atop his biplane’s wing until he banked into a sharp turn.

Even though airplanes flew no faster than birds back then, such encounters could be deadly. Calbraith Perry Rodgers, another early aviator, drowned when a seagull jammed his biplane’s rudder, causing him to plunge into the waters off Long Beach, California. Famous for the first aerial crossing of the United States the previous year—a feat that took him 84 days due to countless mishaps—Cal Rodgers was lamented until public attention shifted to the sinking of the Titanic the following week.

As aviation came of age, faster cruise speeds lent urgency to the issue. Basic physics tells us that force rises as the square of velocity. Thus, colliding with a bird of a given weight will have four times the effect if the impact speed doubles.

Fortunately, the same human ingenuity that gave us airliners has also been addressing this issue. For starters, the global aerospace industry has learned how to make jets and their fanjet engines more robust and tolerant of such events. Design “best practices” and lessons gleaned from operational experience are formalized in the evolving certification standards that govern airframe and engine development.

Among other things, these standards decree that jets must be able to suffer an engine failure at takeoff and still climb safely out. Consequently, all twin-engine types—including the Airbus A320 involved in the January 15, 2009, ditching—are 100-percent overpowered. In practice, this thrust margin means that even when birds are ingested into both engines, enough power generally remains in one or both fanjets for a safe return to the airport. In a rare exception, however, both engines were knocked out last Thursday, and no airplane can sustain flight without power.

The aerospace industry’s many stakeholders—including airports, airlines and other operators, manufacturers, pilots’ associations, regulatory authorities and other government agencies, and interested nongovernmental organizations—have also collaborated with considerable success to reduce the likelihood that aircraft and birds will cross paths in the first place. Guided by data analysis showing where the greatest gains are to be realized, these interdisciplinary efforts gather together experts on flight procedures, bird migratory patterns, wildlife management and emerging technologies.

Because most strikes occur at low altitude when airplanes are taking off or landing, airports landscape to discourage geese, heron, and other large birds from congregating. Airports may also employ noise generators, pulsing or strobing lights, dogs trained to chase birds, and other active but benign measures that discourage resident avian populations.

Commercial aviation is the safest mode of mass transportation in human history and it is getting more so. Nevertheless, US Airways flight 1549 reminds us—fortunately without loss of human life—that we have more to learn on this key front. It also reminds us that when things go badly wrong, as they can every few million airline flights, there is no substitute for a well trained, proficient and professional flight crew.