Air Canada quietly introduced a new feature to the flying public with so little fanfare, I can't even tell you when it happened! Something that you have been able to do on various US airlines for some time, is now available on Air Canada flights... Last Minute Upgrade Purchase.

You have always been able to go up to the desk at the gate and purchase an upgrade, but you would be charged the difference between the fare you paid, and the cost of a full-fare business class seat at that moment. In other words ridiculously expensive. But with this new announcement, although no pricing examples were mentioned, it appears that the costs of the upgrade will likely be fairly reasonable.

As with all promotions or offers there is some fine print, such as having to be departing from a US or Canadian airport, be ticketed on a Tango Plus or Latitude Fare, and it looks like you have to decide at time of check-in, either on-line or at a self-serve kiosk.

Overall it sounds like great news, and a way for a struggling Air Canada to increase revenues, and perhaps open up seats in economy class without having to provide free upgrades. However in the frequent flyer community, red-flags started to go up yesterday regarding the existing upgrade options for status members of Air Canada's frequent flyer program, Aeroplan.

For those not aware, Air Canada provides Elite and Super Elite members with upgrade certificates called SWU (System Wide Upgrade) and SSWU (Special System Wide Upgrade) certificates. These can be used to upgrade Tango Plus fares (with the SSWU) beginning 7 days before your flight for Super Elite members and 4 days in advance for Elite Members or Latitude fares ( with the SWU) anytime before the flight. Now you might be thinking that the paid upgrades are only available 24 hours before the flight, so how would this impact the frequent flyers wanting to use the certificates?

The upgrades that you can attain with the certificates are not automatic if a business class seat is available for sale. They are only available if a special fare class called "I" has space available. Now I am not going to get into the different fare buckets that airlines use to regulate seats and the fares that are paid on a flight, but needless to say Air Canada will reduce the "I" space available before the upgrade windows open routinely, and then you are left to waitlist for the upgrade which sometimes can occur before the day of the flight, but more often than not, you don't find out whether the upgrade cleared until the flight is about to board.

But from an insider at Aeroplan, it appears like the upgrades for purchase will come out of the "I" inventory, which means that if you are using a certificate, your upgrade will have cleared before the upgrades are offered for purchase. If this is indeed the fact, I think it will be good for all involved. Frequent flyers should find their upgrades cleared before arriving at the airport, those without certificates still have a chance at a inexpensive upgrade, and Air Canada should be able to bring in more revenue!

• Darren Mak's blog