use frequent flier miles to upgrade from coach to business class

For those interested in upgrading on airlines flights, there are three ways to get out of coach: qualify for a free upgrade, use frequent flier miles to upgrade to business class service, or purchase an upgrade -- usually by buying airlines upgrade coupons.
US Airways flight upgrade awards allow you to upgrade your purchased fare to a confirmed First Class seat for either one-way or roundtrip travel by redeeming award miles. Upgrades are subject to capacity control, and are only available for travel on US Airways.
As for free upgrades, most us airlines offer them to either elite-level frequent fliers or passengers traveling on full-fare economy tickets (sometimes you have to meet both criteria). These upgrades are generally based on availability and are usually confirmed shortly before travel.
delta airlines gives free upgrades to passengers traveling on full-fare coach tickets to domestic and some international destinations, while United and american airlines reward some elite customers with free e-upgrade or paper certificates based on mileage flown.

For those who aren't elite fliers or don't pay top dollar for a ticket, they can use frequent flier miles to upgrade from coach to business class seats. But here's the catch: even if you are using miles to upgrade, US Airways will only let you do so if you are traveling on an eligible, usually higher, fare.

''I see a lot of people who are on a $99 fare and then they're upset to find out they can't upgrade,'' Mr. Bennett said, which is why he recommends asking if you can use miles to upgrade a particular fare before you buy your ticket. For international travel, he also suggests making sure you are allowed to use miles to upgrade if you are purchasing a ticket that includes travel on an airline's code share partner.

How many miles you need for an upgrade depends on the price of your ticket and the airline you are flying. On US Airways, for example, you need 10,000 miles to upgrade a round-trip domestic ticket if you have bought a full-fare coach or nonrestricted ticket, but 20,000 miles for most economy fares. But United requires 16,000 miles to upgrade a round-trip, full-fare domestic ticket and 30,000 miles for most economy fares. With some airlines, certain discount coach fares cannot be upgraded using miles at all.

The carriers will usually confirm an upgrade using frequent flier miles when you buy your ticket, but upgrades are based on availability and in some cases, an airline won't release seats for an upgrade until shortly before a flight.
Although details of the programs vary, the e-upgrade coupons typically come in 500-mile segments, so you might have to use four coupons for a 1,700-mile flight. If you buy coupons, they generally cost $50 each, meaning a round-trip cross-country upgrade (about 6,000 miles) would cost 12 coupons or $600. Sometimes, discounts are available to elite fliers, customers who buy the coupons online or buy in bulk.

Some carriers also offer customers the option to trade miles for e-upgrades, but for now, you can usually get more value for your miles -- and earlier confirmation of your upgrade -- through the airlines' regular frequent flier programs. But this might not always be a deal. For instance, United requires 50,000 miles for eight e-upgrades -- not enough coupons to upgrade a round-trip ticket from Los Angeles to New York -- while you could upgrade that ticket using 30,000 frequent flier miles.

But before you trade miles or cash for any of these programs, read the fine print. E-upgrades cannot be used on some international routes or with all fares, and in some cases the e-upgrades expire after a year. Indeed, with the cuts some airlines have made recently to business- and first-class fares, those who follow the industry say passengers considering an upgrade should first research what it would cost to simply buy a business- or first-class ticket.

''It's a little-known trend that discounted business-class fares are becoming very inexpensive,'' said Matthew J. Bennett, publisher of Firstclassflyer.com, which offers free advice and a newsletter with tips on ways to fly up front.