Bird strikes have become a growing problem at both the nation’s airports and over low-altitude aviation corridors. For helicopters, the problem is particularly acute, given both the lower cruising altitudes and lighter-weight construction of those aircraft.
The danger was thoroughly illustrated on Jan. 4, 2009, when a Sikorsky S-76C++ operated by PHI Helicopters collided with a red-tailed hawk at 850 feet agl seven minutes after takeoff from Amelia, Louisiana, and crashed into a swamp, killing eight of the nine aboard. The bird penetrated the windshield and, according to the subsequent NTSB accident report, the impact “near the engine control quadrant likely jarred the fire extinguisher T-handles out of their detents and moved them aft, pushing both ECL triggers out of their stops and allowing them to move aft and into or near the flight-idle position, reducing fuel to both engines.”
“Wildlife strikes with aircraft are increasing in the United States and elsewhere," the FAA said. "The number reported per year to the FAA increased steadily from about 1,800 in 1990 to 16,000 in 2018. Expanding wildlife populations, increases in the number of aircraft movements, a trend toward faster and quieter aircraft, and outreach to the aviation community all have contributed to the observed increase in reported wildlife strikes. As a result, there has been greater emphasis on wildlife strike hazard research and airfield wildlife management.”
When the FAA talks about “wildlife,” it is primarily discussing birds. The FAA reports 3,744 bird strikes on turbine helicopters since 2005 and 138 so far this year through September. Of those more than 3,700 strikes, four resulted in aircraft categorized as “destroyed,” with 234 incurring damage classified as “substantial.”
The issue of bird strikes and how to mitigate them was the topic of a panel at October’s Vertical Aviation Safety Team conference with presentations by subject experts including Travis DeVault, associate director for research at the Savannah River Ecology Laboratory at the University of Georgia, and Bradley Blackwell, a research biologist at the United States Department of Agriculture (USDA).
DeVault discussed avian conflict behavior and mitigation strategies based on a variety of studies. He said the empirical evidence suggests that birds are always trying to avoid aircraft collisions, noting that a multiyear study of dead birds found along the runways at New York JFK Airport found that injury locations “tended to be on the ventral and posterior side of those birds. The birds saw them [aircraft] coming and they tried to initiate an avoidance response, they just couldn’t do it in time.”
He said that research also showed that birds initiated the avoidance response at a near-constant distance of 92 feet, regardless of aircraft speed. It also takes the birds a near-constant 0.8 seconds to “clear the path of the vehicle once it starts the avoidance maneuver.” That means that birds typically cannot clear the path of an approaching aircraft traveling faster than 65 knots.
Habitat disincentives that would limit bird water, food, and cover are critical to abatement. DeVault pointed out that the amount of surface turf at U.S. airports is nearly 1,300 sq mi, bigger than the U.S. state of Rhode Island. Non-lethal technology mitigations, such as the use of acoustic devices, show mixed results based on species.
Blackwell said various research on bird reactions to aircraft pulse lighting and various light shades on the IR spectrum held promise. An anecdotal study following the installation of pulse lighting on Qantas Boeing 737s showed a 24 percent drop in strikes and an annual repair savings of $1 million compared to airline aircraft not so equipped.
A study using penned geese and drones showed that pulsing white LEDs initiated a response from the birds that was four seconds faster. The birds tended to initially avoid both blue and red lights but avoided blue the most. However, over time they became attracted to the red. “That’s not a good thing for aircraft,” he said.
Blackwell said continuing research that would conclude over the next year is focusing on “building the first aircraft light that is intended to enhance detection and the avoidance response by birds.”