"When you have a lot of cancellations at the end of a month like this, it is usually a combination of aggressive crew scheduling and/or labor trying to make a point," said George Hamlin, managing director, Airline Capital Associates in New York.

"When a company gets into a tight squeeze, minor slowdowns from the pilots will make quite a difference," he said. "Unfortunately, the people inconvenienced are the people paying both management and labor."

The Federal Aviation Administration allows pilots to be in the air 100 hours a month. Northwest used to schedule for an average of 80 hours a month. Under the more stringent contract the pilots adopted while the airline was in bankruptcy, they are now flying closer to 90 hours a month, limiting their chances of picking up additional routes (and monthly income) and putting the whole airline in a bind when unexpected delays slow it down.

Two weeks ago, the Northwest branch of the Air Line Pilots Association, the union that represents Northwest's 4,800 pilots, issued a vote of no confidence in Northwest's management, mostly over the staffing issue, said Capt. Wade Blaufuss, union spokesman.

"Northwest had not properly staffed the airline for the upcoming summer months, and we were trying to tell them that," he said. "This is a very complicated business. We're not making widgets and selling them at Wal-Mart. There are safety, customer service, security, weather, fuel prices and schedules that have to work in perfect harmony to make this airline run. When you leave so many areas at red line, and something happens, it becomes a spectacular failure because it all cascades."

Northwest would not comment on how much summer travel had increased its work load.

At 5 p.m. Wednesday, Northwest's on-time ranking on Flightstats was 83 percent systemwide but only 62 percent in Detroit, where it had canceled 47 flights and 29 were running 45 minutes late or more.

While local travel agents say end-of-the-month cancellations are common, "Northwest has definitely been leading the pack in the last four or five days," said Rebecca Martin, president at A & I Travel.

"We started being aware late Monday," she said. "By Tuesday, we knew something was up, so we sent communication to our travelers to try to get ahead of it."

Northwest has been doing its best to alert customers too, she said.

"One of our customers got a call Monday morning for a Tuesday morning flight," she said. "With the 24-hour notice, we were able to get them out Monday night instead of Tuesday."

Rescheduling so many flights "of course, is making our days more hectic," Martin said. "Officially, Northwest is telling us they hope the situation eases July 1."

Joe Brancatelli, who runs joesentme.com, a subscription Web site for business travelers, cuts Northwest no slack, saying the cancellations are running so far ahead of what even Northwest predicted, it has not been physically possible for it to alert all customers.

"No one can cancel this many flights and get to everyone," he said. "Last week, Northwest told its employees to expect four bad days with 240 cancellations. Now, it's gotten so out of control, it shows they can't even predict properly."

He expects the same shortage will happen in late July and August.

Others say Northwest could bring management crews in to bolster the ranks, make short-term cutbacks on pilot vacations or selectively cancel flights in advance, which would probably mean weekend travelers would be hit first.

"Business travelers more than leisure travelers need reliability and schedule. Saying your flight was canceled is like saying the dog ate your homework," Brancatelli said. "That's not acceptable in the business world."