Flights usually go on sale up to 11 months in advance of the departure date. On a scheduled airline, this is usually the best time to book airline tickets for cheap (unless there's a seat sale).
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Get last-minute flight deals
Flexibility could help you win those cheap plane tickets. Charter flights are usually operated during peak season to either sunshine or ski resorts, and this is where you could grab that last-minute flight bargain - if you aren't picky about where you go.