What happens when an eight-pound Canada goose plows through the air intake and fan blades of a jet engine at 6,000 feet?
You didn’t think Canada geese flew that high?
Guess again. Geese are regularly spotted at 6,000 feet, which is enough to give the Federal Aviation Authority and jet-engine and airplane manufacturers reason for moderate concern.
Jet engines need to accept a healthy fowl smack and perform efficiently–it’s that simple.
Thankfully, there have been relatively few documented aircraft accidents involving “birdstrikes,” to use industry lingo. Figures from the Office of Public Affairs of the National Transportation Safety Board show 83 reported birdstrikes between 1983 and 1999. Those caused aircraft accidents, of which 11 resulted in fatalities.
Chicago radio legend Clark Weber, a private pilot for 48 years, vividly remembers “hitting a beautiful hawk with the leading edge of my right wing. This must have been 25 years ago. I had a Cessna 182 and was taking off from Palwaukee [Airport in Wheeling], climbing out at 110 miles per hour or so and I simply never saw the hawk … but I felt the hit. There was a jolt, and when I landed I found it had put a four-inch dent in the wing.”
Sherman Cornell, a retired United Airlines captain, flew 40 years and recalls “a half-dozen birdstrikes, though most came early in my career when I was flying DC-3s and C-46s at lower altitudes. The DC-3, which was not pressurized, had a canted window, and there was one flight where the captain was bending over to check something just as a goose crashed through the right window and sent the glass over his head, slicing through the bulkhead on the other side. It would have taken his head right off if he’d been sitting up straight. We had another pilot flying a Convair 580 over Sioux Falls, S.D., who lost an eye when a duck came though his windshield.”
The FAA calls such occurrences FOD, for foreign object damage. Cornell rightly points out that birdstrikes are only one type of FOD.
“You might remember the SST crash at the Paris Air Show in the early 1970s. There was talk at the time that a piece of shredded tire may have caused an engine problem there. [Shredded tires also contributed to the crash last year of a Concorde outside Paris]. Birds are only one issue regarding FOD.”
Perhaps understandably, the FAA and the jet-engine manufacturers are wary of discussing FOD and engine ingestion of migratory birds. Testing is so comprehensive, they don’t feel there is cause to rile up the flying public with sensationalized reports. And there is the danger that some glib writer will poke fun at the testing process.
Example: The old myth about using a British-built catapult to fling dead chickens through airplane windshields. The chickens flew at such force, they blew gaping holes through the wall behind the captain’s seat. The American researchers fired off a query to their colleagues across the pond and received a one-line response: “Thaw the chickens first.”
Funny story, but it never happened.
GE Aircraft Engines spokesman Rick Kennedy said “generally only one birdstrike test is conducted on only one engine during the development phase of any engine program. Once the FAA engine certification requirement is satisfied, further birdstrike testing would serve no purpose. The type and number of birds used in testing is prescribed by the FAA, depending upon the engine being tested. In the case of our GE90, [on the Boeing 777] an eight-pound bird was required, so a Canada goose was used. For earlier generation engines a four-pound mallard duck was used. Medium bird tests require four to six birds, usually Herring gulls weighing 2.5 pounds. Small bird tests use six to eight birds, often California gulls weighing 1.5 pounds each.”
For example, a GE90 requires one eight-pound bird, and a Honeywell 7,000-pound engine requires one four-pound bird.
Kennedy is quick to add that GE Aircraft Engines holds federal and Ohio scientific collecting permits and obtains said geese, ducks and gulls through the Animal Damage Control Office of the U.S. Department of Agriculture, as well as the Fish and Wildlife Services of the U.S. Department of the Interior. “We get accidental kills and kills confiscated from poachers,” he explains.
Jim Kidwell, director of engineering at Honeywell Engines’ Gas Turbine Center, is concerned primarily with smaller jet engines with 3,000 to 6,000 pounds of thrust. Honeywell Engines supplies Business Aviation class aircraft, such as those built by Cessna, Lear, Bombardier and Raytheon.
“The FAA requires us to demonstrate two ingestions of a 1 1/2-pound bird with the engine remaining at a minimum of 75 percent power,” he says. “The reason for a lighter bird, as opposed to the eight-pounder required for that GE90 test, is the design of the Honeywell engine. A smaller engine obviously has a smaller opening, about 3 feet across instead of 10 feet or so with the GE90. We’ll use a small hawk or a small grouse, for example. Imagine something the size of a Cornish game hen.
“Our basic design is what we call a closed core with a high bypass turbo fan. In other words, while air is forced into the burner, that burner is enclosed. Foreign objects such as ice or a bird are turned away from the core by rotating fan blades. They bypass that portion of the engine.”
John Fisher, an engineer with the Engine and Propeller Directorate of the FAA, discussed the actual firing of dead game birds into the jet engines:
“One bird is aimed at the most critical exposed location–often a blade tip or directly into the core,” said Fisher. If the engine gives 6,000 pounds of thrust, the reading must reflect no less than 75 percent of that number as the bird/ice/foreign object passes through.
“The rate of occurrence is estimated at one bird for every 5 million flights,” Fisher adds. “It’s not that frequent. It’s just not that frequent.”
Kidwell mentioned ice as another cause for concern. Standards for ice ingestion are covered by FAA regulation, as is the durability of the fan blade.
“On each engine we’re required to demonstrate a deliberate blade-out. This is where we purposefully fail a rotating fan blade with an explosive charge. We need to prove that the broken fan blade won’t fly loose and cause damage to the rest of the airplane. The blade must remain contained within the engine.”
Icing and ice-slab formation also concern the FAA.
“When a pilot activates the anti-icer, there is, after two minutes or so, the potential for ice slabs to slide off the wings,” says Fisher. “This ice may be ingested into the engines as it falls away, and we need to know what type of damage, if any, that it may do. The chances of such damage occurring are remote, but we have to be sure. We check engines in freezing and fog conditions to make certain the engine doesn’t develop ice.”
Regarding hail damage, the FAA requires testing with simulated two-inch hailstones, after which the engine is shut down and inspected for damage to inlet hardware, fan blades and spinner.
Jim Kidwell at Honeywell Engines places jet engine testing in perspective when he says, “As we’ve learned lessons over the years, we’ve been able to accelerate our mission cycle. On a new engine, there is a minimum of 10,000 hours of testing before it’s introduced. You figure the average engine gets 450 to 600 hours per year of flight time, so you’re looking at 12 to 15 years of average flight for testing and validation of each new generation of engine.”
CHICAGO AVIATION OFFICIALS HARASS, MOVE ANIMALS
How does the City of Chicago Department of Aviation handle nuisance wildlife at O’Hare International and Midway Airports and Meigs Field?
“The Wildlife Services Division of the USDA began working with our staff in 1992,” says spokeswoman Monique Bond. “In a sense it’s management by harassment, and if that doesn’t work, staff will relocate the wildlife.
“Raptors give us the greatest problem. They’re a large bird. They look like a cross between an eagle and an owl. We do have the Canada geese you mentioned, but raptors are what we deal with most often.”
Bond goes on to explain that Department of Agriculture employees use specific pyrotechnic devices that create a loud noise and scare away the birds. Stubborn birds are trapped and removed. Bond says more than 500 birds were snagged and removed between 1997 and 2000.
“And don’t forget about deer strikes,” she adds. “Wildlife Services Division personnel captured and relocated all of the deer that lived on O’Hare property. Our last deer strike was in 1993. Deer-proof fences installed at the time have made all the difference.
“We continuously inspect our runways for anything that might interfere with a flight, whether it’s wildlife or debris that could cause an engine problem. Preventing such incidents is a top priority with us.”
