Tracking radar tested for birdstrike prevention

 - April 3, 2009, 9:35 AM

The US Airways flight that splashed down safely in the Hudson River drew renewed attention to the longstanding problem of birdstrikes. It’s tempting to call the ditching the ultimate birdstrike event. But thankfully, everyone lived, unlike the 62 souls in an Eastern Airlines Lockheed Electra that in 1960 was downed right after liftoff by a flock of starlings–a bird much smaller than the Canada geese that are blamed for the damage to Flight 1549. The Electra’s crash into Boston Harbor marked the highest death toll to date for birdstrike accidents. Yet almost 50 years later, even with warnings of birds in the vicinity, there’s still uncertainty about the actual threat they present until they’re unavoidable, or almost so. What can be done about that? One promising answer is bird-tracking radar.

In the early days following radar’s invention during World War II, researchers regarded the birds it detected as unwanted “clutter” that obscured important information. Only much later were those nuisance returns on the screens of “skin paint,” or primary radars recognized as potentially valuable alerts to pilots, particularly during spring and fall, when millions of migrating birds were on the move. So while today’s primary radars, such as the 200-plus-mile range Nexrad and the FAA’s 60-mile-range ASR-9 and ASR-11 terminal radars, track birds in conjunction with their basic weather role, they only skim the surface at close ranges and, due to the earth’s curvature and the need to avoid ground clutter, their scans soon rise above 3,000 feet agl. But it is at that height and below that most birdstrikes occur.

This has led to the development of airport-based bird tracking radars that scan from the ground up, out to around five miles, using modified marine X-band radars that are common to private and commercial vessels worldwide. Yet how can this be, since airborne weather radars are also X-band systems, and they don’t even show aircraft, let alone birds? The answer lies in the sophisticated signal processing that the researchers apply to wring out the smallest details from the radar returns, thereby detecting not only birds but also smaller creatures such as bats and even swarms of insects.

A Four-pronged Approach
While bird-monitoring radar has been in military use for many years, a four-year collaboration of government, academia, industry and the airport community was established in 2006, to address the problem of civil aircraft birdstrikes. Participants include the FAA’s Technical Center, in Atlantic City, N.J.; the University of Illinois’ Center of Excellence for Airport Technology (CEAT) at Urbana-Champaign, Ill.; Accipiter Radar Technologies of Fonthill, Ontario; and Seattle’s Sea-Tac Airport. Major funding and program oversight comes from the Technical Center, while CEAT provides detailed direction and analysis, Accipiter brings radar and signal processing expertise and Sea-Tac provides the equipment sites and the key knowledge of the airport’s wildlife specialists.

An early product of this cooperative program is a compelling video of an exploding rush of more than 1,000 starlings as they simultaneously left their roosts just outside Sea-Tac at dawn. The radar clearly shows them breaking into separate streams as they crossed the runways at heights between 100 and 300 feet agl, and at speeds of up to 52 mph.

Wildlife experts call the birds “feathered bullets,” and have always considered the movements of their typical whirling mass unpredictable. However, longer-term analysis of the radar data from these and similar flocking birds can be expected to discern patterns in their apparently chaotic maneuvers, potentially making predictions of their aircraft strike potential more accurate. (By contrast, a radar video of Canada geese crossing the airport shows them proceeding in an orderly straight line.)

CEAT is one of several FAA-supported Centers of Excellence, each of which has specific objectives and expertise. Concurrent with CEAT’s bird-tracking radar work, for example, is its evaluation of automatic runway FOD detection systems at Chicago O’Hare, Boston Logan and Providence T.F. Green.

Ecological engineer Professor Edwin Herricks leads CEAT, and he is encouraged by progress so far, but cautions that there is still a long way to go, pointing out that it took many years after the 1985 Delta L-1011 wind shear crash at Dallas/ Fort Worth before the development of flight deck alerting systems.

Many other issues must be resolved, such as who assesses the threat and warns crews, and the method by which warnings are delivered (voice or electronically). Would busy controllers be legally liable if they failed to spot on their tower display birds that then caused problems for an aircraft? Should pilots have cockpit displays of local bird movements and self-separate? How big should the displayed targets be? (At Subic Bay, a fruit bat once destroyed a DC-10 engine.)

Herricks also wants to fuse the tracking data from all the nation’s primary radars and the fine-grain bird radars, and Accipiter Radar is under contract to do this. Just as combining data from the Nexrads and the ASRs provides a composite national weather picture, so can bird movements be presented and analyzed on a national scale. Accipiter’s work commenced in 1995 after a fatal EC-3/ bird encounter at Elmendorf AFB, Alaska, with systems subsequently provided to Navy, Marine Corps and Air Force bases. Seattle is the first U.S. civil airport so far to use bird-tracking radar, but the company is also installing equipment this year at Chicago O’Hare and JFK under the FAA program.

Yet the key input to the FAA’s bird-tracking project rests with the knowledge of Sea-Tac’s wildlife specialists, headed by Steve Osmek. “All wildlife managers,” he told AIN, “know the characteristics of the birds at their airports. But what we badly need–but are not getting–are pilot reports of every birdstrike, however minor. Without that total picture, we can’t do as good a job as they need.”

One sobering fact stands out when discussing birdstrikes. Those feathered creatures aren’t so soft when they are encountered in midair. Osmek has developed a graph showing the impact force exerted by birds of various weights when struck at different speeds. For example, hitting a two-pound bird after slowing to the FAA’s required 250 knots below 10,000 feet has the same effect as being struck by a 10-ton object. Those radars can’t arrive too soon.