Southwest Returns to San Francisco

Additionally, improved instrument landing procedures have enhanced the airport's ability to maintain arrival levels in foggy weather, while congestion dropped after the 2001 terrorist attacks triggered an airline industry restructuring.

Mann said other carriers at the airport will likely all be affected in some way as Southwest competes for passengers. "Southwest drains the pool," he said. "They nick everybody."

Southwest began flying to San Francisco in 1982, but eventually chose to focus on Oakland, building an operation with 142 daily departures. It also has 77 daily departures from San Jose.

Of leaving in 2001, Kelly said, "Back then, facility and runway constraints meant we could not compete and be profitable, and there was no growth potential beyond the 14 flights we had at the time." He noted that service levels at the two other area airports won't be affected.

Southwest's plans reflect its effort to position large numbers of new airplanes. The carrier will add 37 Boeing 737s in 2007, boosting capacity by 8%, and it has 30 firm orders and four options for 2008. This May, it will add new flights on existing routes from Denver, Baltimore and Chicago Midway and will begin Denver to Tampa service.