Migratory Season Heightens Hazard Of Bird Strikes

Air Safety Week, Sept 14, 1998

Geese and swans are social animals and fly in flocks. No jet engine currently operating is certified to ingest even one large goose and continue operating.

The seriousness of an encounter with large birds cannot be overstated.

Late summer and early fall is the time when an estimated 300 million birds in North America and Canada undertake their great seasonal migration to points south. It is a period where the hazard from bird strikes is greater than usual.

The flocks follow four main flyways, namely the Atlantic, Pacific, Mississippi and Central; these flyways follow both coastlines, the Mississippi River and the central plains east of the Rocky Mountains. Weather is the key to the start of the migration; radars will track flocks of thousands of birds headed south. The birds take advantage of the favorable winds as cold fronts move across the country. Indeed, they often will wait on the ground for days until they sense favorable winds aloft.

The hazard from waterfowl is particularly great. Sandy Wright of the National Wildlife Research Center in Sandusky, Ohio, has remarked that when an aircraft collides with a 12 pound goose, the impact has a force equal to that of an elephant stampeding over a parked car. Jets and jet engines are designed and tested today to withstand the impact of birds weighing up to 2.5 pounds, but they are not tough enough to withstand impact with a single goose at high altitude, let alone a large number (for related story, see ASW, July 13).

However, the danger of small birds is not to be discounted. According to an "advice to flight crews" on bird strike hazards prepared by the Air Line Pilots Association (ALPA), "smaller flocking wildlife, such as starlings, which have high body density and often flock by the hundreds or thousands, may have the same effect on aircraft engines...to the point that they must be shut down."

The ALPA memorandum offered these tips:

* More than 90 percent of bird strikes occur below 2,300 feet. If taking off in an area of high bird activity, climb as expeditiously as possible.

* If suddenly confronted with birds en route, pull up rapidly. Birds, when confronted with a collision risk, tend to tuck their wings and dive away from the "intruder."

* Consider slowing down if confronted with bird activity. A slower speed may minimize the damage, given that the impact force is determined by mass times velocity squared.

* Avoid flying over locations that attract fowl. Birds like bodies of water, such as airport retention ponds, lakes and seashores. >> Wright, tel. 419/625-0242; ALPA, tel. 703/481-4440 <<