From a House Budget Committee FAQ:
Q: Isn’t the aviation-security-fee increase just an airline-ticket tax hike?
A: No. After the 9/11 terrorist attack, the federal government took over the cost of providing security for the airlines, which had previously paid the full cost. At that time, a fee was established to cover the cost of the federal government’s new security-screening responsibility. Today, that fee covers about 30 percent of the total cost of aviation security. Under this agreement, the fee will cover about 43 percent of the total cost. For additional background, click here.
That doesn’t read to me like an explanation of why the fee increase isn’t a tax hike on airline tickets. It reads to me like an attempt to justify a tax hike on airline tickets.