Want a free first class upgrade? On Delta, it could soon be hopeless.

 Don't count on too many Delta free upgrades next year. Photo: Delta Air Lines. 

Don't count on too many Delta free upgrades next year. Photo: Delta Air Lines. 

There was a time, not long ago, when frequent fliers who flew more than 75,000 miles per year could upgrade to first class for free on many domestic flights. Unfortunately, that golden period is just about over. 

Delta Air Lines had its investor day this week, where airline executives discussed plans for increasing revenue in 2016. One strategy is to sell more premium seats, not only in first class, but also in Comfort Plus. That's the extra legroom version of coach, with slightly better amenities. 

In the slide below, you can see how Delta plans to continue to increase the percentage of passengers who pay for better seats. Getting to 70% first class load factor seems difficult, as some flights have little premium demand, but if Delta keeps selling $345 roundtrip first class fares between New York and Dallas (as I have seen recently) it should be able to persuade a lot more people to sit up front. 

There is a small bit of good news. Delta is increasing the number of premium seats across its network, as you can see below. 

Airlines are confident now and for good reason - business is strong and fuel is cheap. That should hold in the near future and probably beyond. But the industry is cyclical and at some point, whether next year or in 2020 or 2025, the economy will hit a hiccup. Travelers will probably get spooked and stop buying premium seats so often. When that happens, Delta and other airlines may have a lot of empty seats. If you're patient, maybe the glory days of free upgrades will eventually return. 

If you're looking for ideas on how to score a free upgrade, you may want to read my story published this week by Conde Nast Traveler. If you're a frequent flier, though I suspect you already know these strategies. 

Do you fly often in first class? What's your trick?