For every quarter, the Bureau of Transportation Statistics (BTS) publishes 

very detailed statistics on the cost of flights between a wide variety of US cities

.  They even inflation adjust historical prices to the current quarter!

At the very bottom of their table, they have a row "National Average".  

Once the 2028 Q1 statistics are released, I will calculate the percentage increase in fare prices (((2023Q1AverageFare-2028Q1AverageFare)/2023Q1AverageFare)*100).  

 national average fare in 2028Q1 (2023Q1AverageFare) is more than 33 percent higher than the 

 national average fare in 2023Q1 (2023Q1AverageFare) (e.g. if the result of the above calculation is 33 or higher).  Else, it will resolve no.

If the BTS no longer releases the above statistics (or similar), this market will resolve N/A.  If other edge cases come up, I will use my best judgment to resolve.  Please feel free to bring them up prior to betting!