Respondents, the owner and operators of Michigans Kent County International Airport (collectively, the Airport), collect rent and fees from three groups of Airport users: commercial airlines, including petitioners (Airlines); general aviation; and concessionaires such as car rental agencies and gift shops. The Airport allocates its air-operations costs - e.g., maintaining runways - to the Airlines and general aviation in proportion to their airfield use, and its terminal maintenance costs to the Airlines and concessions in proportion to each tenants square footage. It charges the Airlines 100% of their allocated costs, but general aviation only 20% of its costs. The concessions rates substantially exceed their allocated costs, yielding a sizable surplus that offsets the general aviation shortfall and has swelled the Airports reserve fund by more than $1 million per year. After the County Board of Aeronautics unilaterally increased the Airlines fees, they challenged the new rates, attacking (1) the Airports failure to allocate any airfield costs to the concessions, (2) the surplus generated by the fee structure, and (3) the Airports failure to charge general aviation 100% of its allocated costs. They alleged that these features made the fees unreasonable, and thus unlawful under the Anti-Head Tax Act (AHTA) - which prohibits States and their subdivisions from collecting user fees, 49 U.S.C. App. 1513(a), other than "reasonable rental charges, landing fees, and other service charges from aircraft operators for the use of airport facilities," 1513(b) - and under the Airport and Airway Improvement Act of 1982 (AAIA). The Airlines also asserted that the Airports treatment of general aviation discriminates against interstate commerce Page II in favor of primarily local traffic, in violation of the Commerce Clause. The District Court held, inter alia, that the Airlines have an implied right of action under the AHTA, but not the AAIA, and no cause of action under the Commerce Clause, and that the challenged fees are not unreasonable under the AHTA. The Court of Appeals affirmed in principal part, but held that the Airport had misallocated fees for the cost of providing "crash, fire, and rescue" (CFR) services.

Held:

1. The Court declines to decide whether there is a private right of action under the AHTA, but assumes, for purposes of this case, that the right exists. A prevailing party may defend a judgment on any ground properly raised below, without filing a cross-petition, so long as that party seeks to preserve, and not to change, the judgment. The Airport did not cross-petition on the CFR issue it lost below, and resolving the private right of action issue in its favor would alter that portion of the judgment. Pp. 7-8.

2. The Airports fees have not been shown to be unreasonable under the AHTA. Pp. 8-16.

(a) The AHTA sets no standards for determining a fees reasonableness. In the absence of guidance from the Secretary of Transportation, the Court adopts the parties suggestion to resolve the reasonableness issue using the standards stated in Evansville-Vanderburgh Airport Authority Dist. v. Delta Air Lines, Inc., 405 U.S. 707, for determining reasonableness under the Commerce Clause. Although Congress enacted the AHTA because it found unsatisfactory the end result in Evansville - the validation of "head" taxes - 1513(b) permits "reasonable" charges and the Evansville formulation has been used to determine "reasonableness" in related contexts, see, e.g., American Trucking Assns., Inc. v. Scheiner, 483 U.S. 266, 289-290. Thus, the levy here is reasonable if it (1) is based on some fair approximation of the facilities use, (2) is not excessive in relation to the benefits conferred, and (3) does not discriminate against interstate commerce. Evansville, 405 U.S., at 716-717. Pp. 8