USAirways just announced that they are moving to ‘unlimited space available upgrades’ (and thus eliminating upgrade certificates) in the U.S., Canada, Latin America and the Caribbean beginning in March 2004.
They join Continental, Northwest, Alaska, Delta, and America West in adopting this model — leaving United and American requiring upgrade certificates.
This means greater simplicity for members. It also means less revenue from purchased upgrade certificates. And it also means more competition for upgrades.
In a model where every upgrade requires a certificate, and a frequent flyer isn’t given enough certificates to upgrade every flight, they don’t attempt to upgrade every flight. So lower level elites are able to upgrade more often as a result of less competition. But with unlimited (certificate-free) upgrades, every elite “attempts” to upgrade every flight, and thus upgrading is more difficult.
More information is available at the USAirways website.