Originally Posted by
cinnamon121
Hi.
Is there a way to understand when an airline will change its lowest fare class offering? Is it based on ticket available or timing or both? For example, right now DL shows L and U fares for a flight 9 days in advance. Is this based on availability of tickets assigned to those fare classes (eg "There are only 2 tickets available at this price" per Delta.com) and then the price goes up and the fare class increase?
It's a combination of two things.
First and most importantly: fare rules. Airlines publish a list of fares that have certain restrictions. The more expensive the fare, the fewer restrictions. The most common restrictions are advance purchase requirements (3, 7, 14, 21 days, etc.), day of week (can only fly on off-days such as TUE/WED/SAT), and minimum stay. Fares are assigned a fare basis code that indicates which inventory the fare will use. If your itinerary doesn't meet the fare requirements, it doesn't matter that the plane might be empty and there are still seats available in that fare bucket - you wouldn't qualify for them.
Second, there has to be availability in that fare bucket. If your travel meets the requirements for a fare rule, there also has to be inventory available. If you meet the requirements for TA07A0SP but there is no T availability, you're going to end up buying a more expensive ticket.
Availability *usually* shrinks as you get closer to departure. This is what prompts DL to state "only XX seats left at this price". But most people have no idea what the fare rules are. You could look today and see fares with no such warning and tomorrow they could be double the price because you no longer meet the advance purchase rule that.
There is no sure thing when it comes to knowing what airlines will do, but getting a subscription to KVS or ExpertFlyer will give you some more insight into pricing.