Minneapolis ? Northwest Airlines Corp. got off to a smooth start by keeping its planes flying when mechanics struck. But the real test for the company and its replacement mechanics arrives with a far busier weekday schedule.

The strike began on Saturday, generally the lightest flying day of the week. Northwest averages 1,215 flights on Saturdays – but that increases to 1,381 on Sunday and 1,473 on weekdays, company spokesman Kurt Ebenhoch said Sunday.

The airline will find that maintaining its schedule will be tougher as the work week begins, said airline consultant Scott Hamilton, an airline consultant for Leeham Co. in Sammamish, Wash.

“Sooner or later if the replacement mechanics can’t keep on top of it, it’s going to start causing cancellations,” he said.

Northwest’s unionized mechanics, cleaners and custodians walked off the job Saturday morning after refusing to take pay cuts and layoffs that would have reduced their ranks almost by half. No new talks have been scheduled.

Northwest said there were few cancellations and most flights were on time, though the company declined to provide specifics.

Terry Trippler of cheapseats.com, a ticket fare Web site, said Northwest’s schedule had recovered from a work slowdown just before the strike began Saturday morning. Northwest apologized to passengers for delays then, and said it would work to resolve them.

“This weekend has gone much much better than I think (the union) thought it was going to, and maybe a little bit worse than Northwest wanted it to,” he said.

Northwest said there were few cancellations and most flights were on time, though the company declined to provide specifics. The nation’s fourth-biggest carrier switched to its fall schedule Saturday, a week earlier than planned, lightening the schedule by about 17 percent.

Between 6 a.m. and 10 a.m. CDT Sunday, Northwest had 85 delayed flights at Detroit Metropolitan Airport and 68 at Minneapolis-St. Paul International Airport, said Bob Rose, president of Local 5 of the Aircraft Mechanics Fraternal Assn. The local represents 916 Northwest employees in Detroit. The company had 234 delays at those two airports on Saturday, Rose said. He did not have data on canceled flights.