The nation’s two largest airlines, with the largest co-branded frequent flyer credit card programs, are trying to woo business and elite level travelers back into the sky. Tomorrow, United Airlines will permit its “1K Flyers” to upgrade any fare, worldwide, on United’s system through February 29, 2004. Two weeks ago United issued its most frequent flyers four “Sweet Spot Certificates” to use for the special upgrades. Earlier this year “1K Flyers” also received the annual allotment of at least six system-wide upgrades, which carry some new restrictions. United also announced last week that “United First” and “United Business” class passengers who purchase a qualifying international roundtrip ticket on United for travel between now and September 14th, will earn a free award ticket valid for travel to any of over 650 destinations around the world served by United and the Star Alliance carriers. Last month, United launched a promotion offering a free domestic roundtrip for flying three paid, qualifying roundtrip trips on United or United Express between June 5 and September 30, 2003. Meanwhile, American Airlines, last week announced its “Free Ride” program. AAdvantage members who purchase a qualifying first- or business-class round-trip ticket on American Airlines to or from Europe, Japan, Argentina or Brazil between now and September 14th, can earn a free economy-class award for round-trip travel to more than 880 destinations on American and any of more than 20 other AAdvantage participating airlines. For more information visit www.ual.com or www.americanairlines.com.