Birds and airplanes will always share the sky. The challenge is keeping them apart.

On Thursday, crews at Minneapolis-St. Paul International Airport learned just how to do that by firing small fireworks-like devices into the air, creating a loud boom or a noisy screech over the field 100 yards away. They also fired nets from cannons to learn how to catch birds that had settled on airport property.

The number of bird-plane collisions has been growing nationally simply because there are more birds -- thanks in part to conservation programs -- and planes in the air than ever. Also, as awareness of the problem has increased, reporting has improved -- but still, according to Federal Aviation Administration estimates, only 20 percent of bird strikes are reported.

Nationwide, according to the FAA, 7,439 bird strikes to civil aircraft were reported in 2007, with 122 of those in Minnesota. MSP, which keeps track of its own data, reported 99 "wildlife strikes," most of which were birds, that year. Worldwide, 219 people have been killed as a result of bird strikes since 1988 and millions are spent each year repairing planes, according to the Bird Strike Committee USA, which studies bird strikes and how to prevent them.

"No matter what we do, no matter how much we spend, we will not be able to prevent aircraft from hitting birds," said John Ostrom, the manager of air operations at the airport who is also chairman of the committee. "The only way to do that is to take birds out of the sky or to take us out of the sky."

The Hudson River splash landing in January called attention to the dangers of bird strikes. US Airways Flight 1549 lost power in both engines after hitting a flock of Canada geese at 3,200 feet over New York, leading to the "miracle on the Hudson" landing.

Ostrom said MSP has been fortunate to have never had a catastrophic bird strike, despite its location near the 14,000-acre Minnesota Valley National Wildlife Refuge, which spans 99 miles of the Minnesota River. "Knock on wood, we have not had a major incident or accident here at MSP because of wildlife," he said. "We've had some close calls, mind you. But we've never lost an airplane or had a fatality due to a bird strike."

Among the close calls was a DC-9 that encountered 50 swans in March 2000 at approximately 800 feet. The plane struck one, causing "significant damage" to the engine. In 1993, a 747 went through a flock of 400 starlings, damaging two of the four engines, one of them significantly. In both cases, the pilots returned to the airport and landed safely.

Ostrom said about 25 bird strikes are reported each day in the United States, most of which cause minor or no damage to the plane.

The FAA, which estimates that only about 20 percent of bird strikes are reported, currently releases general information about bird strikes, such as how many occur in each state, but has not released numbers for specific airlines or airports.

FAA spokeswoman Laura Brown said Thursday that a comment period on whether to release the more detailed data ends Monday. She said she expected the agency would release the data, possibly as early as next week.

Targeting Canada geese

At the airport, feathered enemy No. 1 is the Canada geese, because of their large size and habit of flying in large groups, followed by starlings, then raptors such as hawks, Ostrom said.

The airport has 22 noisemaking propane cannons that can be activated remotely, but crews also modify wildlife habitat. Canada geese love Kentucky bluegrass, so they avoid planting that. Nets are placed over ponds to keep geese and other birds away. Stuffed coyotes and foxes that move in the wind also deter birds from coming around.

But what works for one species doesn't work for another. Some cannons have recordings of distress cries that are used to scare away starlings or gulls, Ostrom said. But doing that attracts the raptors, which are always looking for easy prey.

Some birds that are caught, such as eagles and snowy owls, are banded and relocated. Others, such as the many captured starlings, are killed.

'Giant vacuum cleaner'

So how can Canada geese bring down a jetliner, as they did on Flight 1549?

Dale Oderman, associate professor of aviation technology at Purdue University in Indiana, described a jet engine as a giant vacuum cleaner.

"It's got the big opening on the front with compressor blades spinning in the compressor section. Their sole purpose is to bring in a huge volume of air and compress it before that air and fuel are mixed and ignited to create thrust from the engine," he said. "Anything that's in the engine's way gets sucked up."

Most of the time, a bird causes fairly minor damage to an airplane such as a dent or cracked windshield. But if a bird -- or mammal, say a deer -- is ingested, the engine's delicate fan blades can be damaged or broken. They can act like shrapnel, damaging other blades and causing the engine to shut down or start on fire.

What happened on the Hudson flight -- both engines getting hit and shutting down -- is very rare, Oderman said.

Jets and jet engines are designed and tested to withstand the impact of small birds, but they are not tough enough to withstand impact of larger birds. Any devices added to the front of an engine, say mesh, would add to the weight of the plane and could itself break off, he said.

Beyond birds

A handful of the strikes on the ground at MSP have been small mammals, including dogs and rabbits, that haven't caused a problem, said Ostrom. If a deer gets on airport property, it is immediately taken out by a sharpshooter.

"What a deer will do to a car it can very easily do to an airplane. It can be ingested into an engine. Most of the airplanes landing here have low-profile engines that are hanging on the wings. So they're actually low to the ground," he said. "There is a significant potential for damage with an animal that weighs 100 pounds."

Suzanne Ziegler • 612-673-1707