Airplanes share the air with birds and the ground with animals. Unfortunately, bird strikes and animal strikes are a serious economic and safety problem.
Researchers estimate that wildlife strikes have cost the civil aviation industry more than $300 million a year every year for the last decade. Add in the cost to military aircraft, and the costs resulting from wildlife strikes likely exceed $500 million a year in North America alone. The cost isnt just financial, either. More than 300 people have been killed worldwide from bird strikes.
Many airports are located close to water and have large expanses of grass – both of which are attractive to birds and other wildlife. Many times there are nearby woods, wetlands or scrub not frequented by people. The more wildlife there is, the more of a threat animals become to aircraft operations.
Airport managers and the FAA have concluded that management programs to reduce wildlife activity on airports are critical because more than 80 percent of wildlife strikes occur in the airport environment. That is not to say, however, that all wildlife species are equally hazardous to airplanes.
Finding the right method to repel birds or other animals depends on the kind of animal. And in developing priorities for fighting wildlife hazards, its important to know the relative risk posed by various species. That fixes the attention – and the dollars – on the species that present the most hazard.
The FAA has a standard form (5200-7) for reporting aircraft strikes by birds and other wildlife. Filing the report is strictly voluntary. Although the FAA has monitored these reports since 1965 to determine general patterns, no quantitative analyses of these data were conducted until the last few years.
The U.S. Department of Agricultures National Wildlife Research Center, through an interagency agreement with the FAA, initiated a project in 1995 to obtain more objective estimates of the magnitude and nature of the wildlife strike problem nationwide for civil aviation. The scientists wanted to rank various wildlife species observed on and near airports in the United States as to their relative hazard to aircraft. They based the rankings on the strike statistics generated by the FAAs National Wildlife Strike Database.
The study covered 21 wildlife species or species groups for which there were more than 17 strike reports from January 1991 to May 1998. For each of these species or groups, strikes were categorized by the reported extent of damage and the effect on flight.
The data was then used to estimate the percentage of strikes causing damage, major damage (i.e., aircraft destroyed or substantial damage incurred), and any effect on flight. These three variables were used separately to rank the species groups as to their relative hazard to aircraft.
The scientists then developed a composite ranking by comparing the relative rank of each species group with every other group for the three variables. Finally, a relative hazard score was developed for each species group by summing the percentage values for the three variables and scaling the scores downward.
The database contained reports of 18,083 strikes from January 1991 to May 1998, of which 52% provided no information on the species of wildlife struck. For the 21 species groups selected for analysis, there were 7,876 reports. The actual species was identified in 2,669 of these reports. Sample size ranged from 17 strikes for pelicans to 2,599 for gulls.
Airport operators typically are faced with a diversity of wildlife species in the airport environs that may be struck by aircraft. For example, at least 56 different species of birds were struck by aircraft at JFK International Airport from 1979 to 1992. Furthermore, wildlife management plans implemented on airports to discourage certain species (e.g., tall grass for gulls) may increase the abundance of other species such as small mammals and raptors.
Analyzing the relative risk of each species should help airport managers determine how to modify their wildlife management plans in order to focus their efforts on the species most likely to cause damage.
The rankings and relative hazard scores are based on empirical data and thus represent predicted hazards based on past experience. One variable ignored in this analysis was the number of individual animals involved in a strike event. Obviously, an aircraft striking a large flock of birds is more likely to have damage or a negative effect on flight than an aircraft striking a single bird.
For example, bird strikes that resulted in 62 people dying in Massachusetts in 1960 and 35 people killed in Ethiopia in 1988 involved flocks of starlings and speckled pigeons, respectively.
The number of birds struck is usually not noted accurately on strike reports, which is why researchers ignored this variable in their study. However, because the analyses are empirically based, flock size is incorporated into the rankings and hazard scores were based on the patterns of effects and damages that have occurred for the species groups.
The energy dissipated during a wildlife strike is directly proportional to the mass of the animal struck and the square of the velocity at impact. Data on bird ingestions by engines of Boeing 737 aircraft confirmed that for any given velocity, the probability of engine damage increased with the mass of the bird.
Relative hazard scores, based on actual strike data, also were correlated with body mass. Thus, the system of rating relative hazard by various wildlife groups conforms to the expected pattern of increased hazard with increased body mass. There were, however, a few surprises.
Vultures and ospreys showed a greater-than-expected hazard score relative to their body mass, whereas coyotes showed a less-than-expected rating. Vultures and ospreys perhaps soar at higher altitudes than most other birds commonly struck by aircraft and thus are more likely to be hit by aircraft traveling at greater velocities, resulting in greater damage. Coyotes had a relatively high ranking for effect on flight, but lesser rankings for damage because when they are seen on runways pilots frequently abort takeoffs or landings, however, most coyotes are struck by aircraft landing gear or wheels and do little damage.
The initial rating system provides a useful guide to assist airport operators and biologists in prioritizing management actions to reduce strike hazards. These hazard ratings should be used in conjunction with site-specific wildlife surveys to determine relative abundance and use patterns of wildlife species for the airports in question.
A critical action needed to improve the rating system is to increase the identification of species struck by aircraft, which presently stands at less than half of the incidents in the National Wildlife Strike Database. Wildlife biologists can usually identify carcass remains (if saved) by species. Specialists can identify even small fragments of feathers or tissue by species group.
With a larger sample size of strike reports identified by species, researchers can provide more accurate estimates of the relative hazard among species, as well as refine estimates for such factors as aircraft and engine types. This would allow adjustments of the hazard ratings for airports with different air-traffic characteristics such as large commercial passenger jets, small corporate jets, propeller-driven aircraft, helicopters or specialized military aircraft.
Personally, my first close encounter with animals while flying came while I was taking flying lessons at Willow Run in Ypsilanti, Mich., where we almost hit a coyote crossing a runway while landing. Ive seen coyotes on several airports since then, and even in urban environments you can find deer, coyotes, beaver, and other animals you might not expect to find.
Being based in Michigan has its own nuances (as do other geographical locations) when it comes to flying and animal encounters. The Great Lakes basin hosts large migrations of waterfowl, and even raptors, during certain times of the year.
A few months ago I was flying back to my home base in Traverse City when I had a close call with a seagull at 4,500 feet. I was receiving flight following from Saginaw, had the auto-pilot engaged, and was sitting back enjoying the ride when a speck appeared directly in front of me. Im sure I scared my passenger nearly to death when I grabbed the yoke and blurted out an expletive with a shocked look on my face.
At 160 knots the gull went from a speck to a flash over the wing in about three seconds. All my passenger saw was a blur as the gull passed three feet over the outboard section of the wing.
The gull may have heard or seen me coming, but neither of us could have really done much to avoid the potential conflict. In another recent incident, I flew into Fort Lauderdale/Hollywood International and flew right through a wake of vultures, just missing one on the base leg.
It helps to know the hazard rankings so you can assess the situation and determine the best course of action. If you encounter a coyote or a deer on the runway and a collision is imminent, consider the possible consequences. Coyotes are low on the damage scale, so it may be better to proceed straight ahead rather than groundloop or otherwise depart the runway. If it is a deer on the runway, you may be better off maneuvering, or even leaving the runway, rather than hitting one head-on.
Report strikes, either through the form or on-line at www.birdstrike.org. Reporting strikes – including supplying remains so the proper species can be identified – will help researchers provide even more valuable data in the future.
Also With This Article
Click here to view “Ways the Damage Gets Tallied.”
-by Kevin Clark
Kevin Clark is president of Critter Control Inc., one of the nations leading wildlife control companies. He is a 1,000-hour commercial/instrument pilot who flies a Piper Saratoga.