Elite status in an airline’s frequent flier program can bring many perks, from free checked luggage, to bonus miles, to priority waitlists and upgrades. United Airlines is now changing one of their freqent fliers’ most cherished perks.

Since they are prioritized by status, those upgrades are often available only to the highest level fliers. But for years, all elites in United’s Mileage Plus programs have had one of the simplest and most sought-after perks — access to extra legroom in the Economy Plus section.

Most carriers now have some sort of “premium” seating available in coach for an extra charge or for their elite members. However, with most legacy carriers, the only thing “premium” about the seats is location. It might be an aisle or window seat towards the front of the cabin, but it’s the same seat with the same legroom as in the back.

(Exit-row seats are a notable exception, but most airlines don’t allow them to be preassigned at any price, except for their highest-ranking fliers.)

On the other hand, United’s Economy Plus is a genuinely better experience. I’m 5’3″ and, even for me, the extra space feels a lot more comfortable. It’s also much easier to get in and out of the seat. For anyone using a laptop or even using their tray table for meals, it means not feeling completely pinned in, especially if the person in front reclines. Some of my clients tell me it makes the difference in whether or not they can work on the flight.

Many regular travelers tell me they prefer a middle seat in economy plus to an aisle or window in back.

United just sent an email to frequent fliers talking about the changes to their Mileage Plus program for 2012, as they continue on their merger path with Continental. Many of the changes, which will no doubt be covered in future posts on Consumer Traveler, look promising. (Particularly intriguing is a fourth level — Platinum — for anyone who flies between 75,000 and 100,000 miles a year. Along with what seems to be a return to same-day, free flight changes for higher elites.)

Depending on mileage level, one change stands out, and for the lowest-level elites, not in a good way. For these basic premiers (Silver level, 25,000-49,999) miles a year, Economy Plus seating will still be available, but ONLY at time of check-in.

The email didn’t state whether this means only on the day of departure or for online check-in the day before. In any case, it means that on popular routes, these travelers are either going to end up in the back of the bus or paying additional fees like no-status travelers.

Now of course, Economy Plus seats MIGHT be available on day of departure, but in my experience with the San Francisco to Dulles flights, such seats are never available even two or three weeks in advance. In fact, I just booked a 100,000 mile a year flier today on such a flight for October 10, almost three weeks from now, and only one of United’s ten nonstops had an economy plus aisle available.

On a positive note, restricting the lower level premiers might open up more seats for more frequent fliers. (Although it is anyone’s guess whether those newly opened seats will be quickly filled by travelers paying the surcharge.) And while my experience is limited to our agency clients, friends and readers, my sense is that United must have been receiving angry emails from high-level fliers who ended up stuck in a lousy seat in back.

On the other hand, some travelers who, whether they only fly somewhat regularly, or just end up splitting their travel between different carriers, are going to be hugely disappointed, especially those who have arranged their 2011 travel in part to qualify for United’s Premier level.

My sense, however, is that this change will stick. For the airline’s biggest spenders this will be a positive development. Which means for many travelers, 2012 may mean “Fasten your seatbelts, it’s going to be a cramped ride.”

Photo: johnnyjet