The number of passenger complaints about U.S. airlines fell in September for the first time this year, dropping to 5,143 from 6,822 in August.

The total was the lowest since May, when complaints filed with the Transportation Department began to rise sharply. But it still was high compared with last year.

Northwest Airlines, which has been troubled by labor unrest, ranked highest for the second month in a row, with 33.62 complaints for every 100,000 passengers carried. That was down from 47.36 complaints per 100,000 in August.

Continental, which led the complaint list for several months, ranked second.

Complaints against the Texas Air Corp. subsidiary dropped from 38.6 per 100,000 in August to 24.65.

Pan American World Airways, Hawaiian Airlines and Eastern Air Lines -- another Texas Air unit -- were in the top five, followed by Trans World Airlines, Midway Airlines, United Airlines, Jet America Airlines and Braniff Inc.

The lowest level of complaints registered by a major U.S. airline was for Delta Air Lines, which attracted only 2.86 complaints per 100,000 passengers.

Earlier this week, the department reported that flight delays decreased in September -- in part because of new air traffic routes, in part because of revised and more realistic schedules being published by the airlines, and probably in part because of better weather this year than last.

Airline service has become a major issue this year. The Transportation Department this month will begin collecting data from the airlines that will provide consumers with more information about different aspects of service, such as on-time performance and baggage handling.

In addition, Congress is moving to require similar reports from the airlines and may also impose penalties on airlines that lose baggage or that cancel flights without a safety-related reason.