An available seat mile is the fundamental unit of production for a passenger-carrying airline.

Revenue for each seat mile flown was down 10 percent as the boom in business travel of the late 1990's ended abruptly.

But after the attacks, revenue per seat mile plunged 40 percent.

Both revenue and the cost per available seat mile, a standard measurement, were exceeding projections, he said.

The system has reduced American's labor costs by 7 percent, to $2.84 per available seat mile in 1987, from $3.05 in 1983.

United's labor costs have declined by only 4 percent to $2.83 per available seat mile in 1987, from $2.95 in 1983.

United grew by only 2.8 percent last year in terms of available seat miles, compared with 12.9 percent for American.

As a regional carrier, its costs per seat mile were three times Southwest's.

A seat mile is the cost of carrying a passenger one mile.

Available seat miles, which measure capacity, were up 12.4 percent in February over the year-earlier month, the agency said.