It's my understanding that AA employees can use SOS's they receive to pay the taxes and fees associated with "free" tickets.
The Federal security fee is a separate issue. It was not in effect when an AA employee gave me this information. Also, this is unrelated to the treatment of this benefit as taxable income, which I believe has already been answered completely.
(For the AA-impaired: an SOS is a coupon that a passenger gives an employee as a "thank you" for outstanding service. The letters stand for "SomeOne Special." AA mails them to elites from time to time. Elites who use them up can get more, and others can get them, on request. They can be redeemed for a variety of other things too, as well as generating a positive note in the person's employee file.)