Bird Strikes on Aircraft: What's the Risk?

It's hard to imagine what the passengers of US Airways flight 1549 experienced in January 2009. Only minutes after takeoff from New York’s LaGuardia Airport, an emergency forced Captain Chesley “Sully” Sullenberger to land in the Hudson River. Thankfully, all aboard survived what instantaneously became an international news story dubbed "Miracle on the Hudson."

Unlike most aircraft accidents which involve painstaking investigation to identify the cause of the calamity, in this case the captain’s radio transmissions with ground control provided a strong clue as to what caused this accident: geese.

This was not the first aircraft accident attributed to birds and it won’t be the last, but it did, thanks to extensive media coverage, highlight the issue of bird strikes on aircraft. Ironically, the very animals who provided man with a dream to fly have become a threat, albeit extremely remote, to aircraft.

Bird strikes to aircraft are a reality. While the vast majority of reported bird strikes are of no consequence to people, failing to cause any aircraft damage or delays, on occasion bird strikes cause damage (in some cases substantial), emergency landings, flight delays, and, though extremely infrequent, aircraft accidents. Some of these accidents end in tragedy such as the 1961 crash of an Eastern Airlines jet into Boston Harbor after it struck a flock of starlings, killing 62 passengers, or the 1995 crash of a Boeing 707 AWACS aircraft that struck Canada geese after taking off from Elmendorf Air Force Base in Alaska. All 24 on board were killed.

Though tragic, not only are such accidents exceedingly rare, but the risk of a bird striking an aircraft is miniscule. This key fact, not reported by the media in light of “Miracle on the Hudson,” is also ignored in various relevant scientific studies.

Though rare, there are many identified causes of bird strikes. A number of the nation’s airports are located within migratory bird flyways and/or provide extensive habitat for birds to roost, rest or feed. For example, JFK International Airport in New York is adjacent to the Jamaica Bay National Wildlife Refuge, a renowned birding spot where thousands of birds stop during migration. In addition, some bird populations are increasing, aircraft operations have largely increased over the years, and aircraft engines are quieter which, according to some experts, has reduced the ability of birds to detect and avoid oncoming aircraft.

According to bird strike data compiled by the federal government, more than 369 species of birds have been involved in bird strikes from 1990 to 2007 ranging from sparrows and starlings to eagles, geese, gulls and herons. Smaller-bodied birds, like sparrows, are often referred to as “feathered bullets” because of the extensive damage they can cause to aircraft engines when ingested while the sheer size of the larger birds, like Canada geese, pelicans, vultures and eagles also pose threats to engines and other aircraft parts if struck. According to government bird strike data the bird groups most commonly involved in bird strikes in the United States are gulls, doves and pigeons, raptors and waterfowl.

While the sheer number of reported bird strikes, the number of species involved in strikes and a plane landing in the Hudson River are enough to make many question the safety of flying, the reality is that air travel remains extraordinarily safe. Bird strikes, though receiving considerable attention when causing an aircraft emergency, are extraordinarily rare events.

According to government wildlife strike statistics, there were 7,516 reported wildlife strikes (including 7,286 bird strikes) on civil aviation (non-military) aircraft within the United States in 2008. The reported bird strikes resulted in “substantial” damage to 79 aircraft—damage that affects the aircraft’s structural strength, performance or flight characteristics and normally requires major repairs. To place these statistics into a national context, according to US Department of Transportation data in 2008 (the latest calendar year available for statistics), there were a minimum of 54,823,492 airport operations (defined as the number of arrivals and departures at US airports of air carrier, commuter/air taxi, general aviation, and local aircraft), providing transportation for 736,470,443 passengers. With a reported 7,516 wildlife strikes, approximately .013 percent of all aircraft takeoffs and landings struck wildlife. The government claims that only one in five (20 percent of) bird strikes are reported. Yet, assuming this is accurate, even if 100 percent of all strikes were reported, this would still mean that less than .068 percent of all aircraft operations struck wildlife.

While the five human fatalities attributed to wildlife strikes in 2008 were unfortunate, considering that nearly 736.5 million people traveled by air via US airports, the risk of being killed as a result of a wildlife strike is nearly non-existent.

Nationally, from 1990 through 2008, there were a reported 87,416 bird strikes on aircraft. Of the 68,653 bird strike reports providing information about damage to the aircraft, 59,047 strikes resulted in no damage, 5,112 resulted in minor damage, 2,455 resulted in substantial damage, 2,015 resulted in uncertain damage, and in 24 instances the aircraft was destroyed. During that 18-year period, there were 1,151,813,266 airport operations (excluding military airports). Based on those statistics, the risk of an aircraft experiencing a bird strike was less than .0076 percent. Again, even if there was 100 percent reporting of all bird strikes, the risk of an aircraft striking a bird would only increase to approximately .0379 percent. Of the 24 aircraft reported destroyed due to bird strikes, 15 were considered small aircraft (2,250 kg), six were medium-sized aircraft (2,251-5,700 kg), two were large aircraft (5,701-27,000 kg), and one was a very large aircraft (27,000 kg).

During that period, tragically, 15 people died as a result of bird strikes on aircraft. The estimated number of airline passengers departing from or arriving at US airports over those 18 years, according to government data, was nearly 12.5 billion passengers, reemphasizing that the risk of being killed as a result of a bird strike is extraordinarily miniscule.

Responding to Bird Strikes
Despite the infrequency of bird strikes on aircraft, efforts are being made worldwide to further reduce this remote risk. In the United States, the FAA requires most airports to develop Wildlife Hazard Management plans to identify and mitigate wildlife threats to aircraft. It also has promulgated regulations requiring select aircraft parts, like engines, depending on their size, to be able to withstand the ingestion of small, medium and large-sized birds (up to 8 pounds) without losing a certain percentage of power and thrust, catching fire or failing to contain any engine debris within the engine cowling. While there are presently no engine ingestion certification standards for larger-bodied birds such as vultures, eagles and herons, the vast majority of reported bird strikes involve small birds weighing less than 2.5 pounds.

Airport authorities throughout the country, given their responsibilities for the safety of millions of airline passengers and to avoid legal liability in the case of a crash, also actively work to reduce, eliminate and prevent wildlife strikes. In some cases, non-lethal strategies are used such as airport water management (eliminating temporary or permanent ponds that may attract birds); vegetation management (planting certain species of, or managing the vegetation to, reduce the attractiveness of the airport to birds); sanitation management both on and off airport properties (to reduce availability of potential food sources); fencing and barriers (preventing wildlife from accessing airports); human management (reducing intentional feeding of birds by cab drivers, airport staff and the public); improved radar to detect flocks of birds traversing the airspace and the use of devices to disperse birds (cracker shells, pyrotechnics, dogs, trained raptors and radio-controlled model airplanes).

Unfortunately, despite the extremely remote risk of a bird striking an aircraft, let alone causing substantial damage or an accident, lethal bird control is also practiced at many airports. Nearly 570 depredation permits have been issued by the US Fish and Wildlife Service allowing the harassment and killing of migratory birds at U.S. airports. Most lethal control efforts, however, are conducted by the USDA’s Wildlife Services program. Wildlife Services personnel provided technical assistance to address wildlife (including bird) management issues at 714 airports and military airbases. Wildlife Services conducted lethal control at 235 airports, employed non-lethal dispersal techniques at 218 airports, performed habitat modification at 158 airports and captured and translocated wildlife at 75 airports. During fiscal years 2007 and 2008, according to data provided by Wildlife Services, 164,918 and 136,890 birds at US airports—including military airports—were killed by Wildlife Services, respectively. At JFK Airport in New York alone, Wildlife Services personnel killed 72,063 gulls, including 63,838 laughing gulls from 1991 to 2002.

Despite its continued use of lethal bird control to address a risk that is, by all measures, extremely remote, the USDA’s Wildlife Services program continues to develop non-lethal options to reduce the attractiveness of airports to wildlife, to make aircraft more noticeable to wildlife and to more effectively disperse wildlife as necessary to protect aircraft and passengers. Ideally, it should emphasize such non-lethal options and forego future lethal control given the statistical evidence of the remote risk of bird strikes to aircraft.

For those who travel the United States or the world, there is no need to significantly concern themselves or alter their mode of air travel due to bird strikes. Indeed they have a greater risk of being in an accident driving to work or being struck by lightning than being injured or killed as a result of a bird strike.

Paying the Price
Sadly, some six months after the miracle, New York City Mayor Bloomberg, in cooperation with state, federal and airport authorities initiated a massive goose capture and euthanasia campaign targeting upwards of 2,000 geese within five miles of La Guardia and JFK airports. While this effort may have violated state and federal law, in press reports announcing the operation Mayor Bloomberg callously asserted that “there is not a lot of cost involved in rounding up a couple thousand geese, and letting them go to sleep with nice dreams.” Of course this effort, though it may have placated Mayor Bloomberg’s fear of geese causing another aircraft accident, did nothing to reduce the already remote risk of bird strikes on aircraft in the New York metropolitan area.

See chart “By the Numbers” bird strike data for the 10 busiest US airports in 2008 in the Winter 2010 AWI Quarterly PDF.