Smarterliving.com has two new useful columns on upgrades. First is a piece by Tim Winship on affordable first class and second is an article by Erica Silverstein on upgrading with miles.

Both are useful and worth reading, although it’s always worth remembering that any time you try to tackle such a broad subject across a range of carriers, the devil will be in the details and some small items will be wrong or misleading.

Contra-Winship, not all carriers offer unlimited domestic upgrades to their elite members. United, for example, does not.

Erica Silverstein offers a bit of confusing prose about what fares are eligible for upgrades on US carriers.

Northwest allows all but the most deeply discounted fare classes to be upgraded; and Delta only allows full-fare economy economy tickets to be upgraded.

She’s correct about Northwest with respect to domestic tickets — elites can upgrade pretty much any fare, and non-elites can upgrade most fares (but not the cheapest). Internationally, Northwest allows mileage upgrades only on full fare (Y and B) across the Atlantic and on almost full fare (Y, B, and M) across the Pacific.

Delta allows full fare tickets to be upgraded internationally as well as M fares which are a notch below full fare.

Similarly there’s a bit of confusion on partner upgrades

United and US Airways do not seem to allow upgrades on their partners.

While United and USAirways do not allow mileage upgrades on each other (though elite members can purchase upgrade certificates and use those), United does permit upgrades with miles on its partner Lufthansa.

So always worth reading upgrade primers. Just know that you still have to check the details for each carrier. Or drop me a note and ask, and I’ll dig up the details for you.