Trying to figure out good times to purchase airfare is like playing the craps tables in vegas. A little luck will get it for you. It does appear that the best rates seem (but in not all cases) to be the lowest at the 331 day point.
By doing alot of searching and searching, you just may be able to see a pattern on the times that the particular airline's fares fluctuate.
I just recently purchased tickets that i studied for 2 months and noticed what appeared to be pattern. I decided on a reasonable price and watched it maintain itself for a couple of weeks. Some other fares of interest seem to change on the first part of the week. On the monday, two weeks later, i purchased the tickets, selected seat assignments and received confirmation. 15 minutes later i returned to the same flight times and the price had increased by $50 and has stayed there for the last several weeks. There is no set pattern, you just have to do some intensive searching at times to find the lowest fare that you can live with.
This by no means is no solution, just my 2-cents worth. You gotta search, search and search. Don't completely give up when you see the high fares but watch them closely because if you don't, then they will change when your eyes blink!
If there is anyone out there would could predict the best times to purchase airfare, then they could become instant millionaires
