concurring.
I join in that portion of the majority opinion holding that the airlines were not holdover tenants under Indiana law. I agree with the majority’s conclusion that the ordinances establishing user fees for *1273the Indianapolis International Airport1 are invalid. However, I reach that result for reasons different from those of the majority, and thus, I concur only in the judgment as to the remaining issues.
I
In this appeal, the Indianapolis Airport Authority has asked this court to require the airlines to pay the fees established in its ordinances for use of the airport. The airlines argue that the ordinances, and more particularly the user fees charged them under the ordinances, are invalid because the Airport Authority improperly allocated costs among airport users in setting the fees. In response to these arguments, the majority opinion informs the parties that the ordinances are invalid because the airport has a monopoly and extracts a monopoly price from the concessionaire users. The majority opinion argues that the ordinances are invalid because the fees charged to the concessionaire users are excessive, resulting in an unreasonable price being charged to airline passengers. There are several difficulties with this approach. First, whether the fees charged to the concessionaires are excessive is not at issue. No one, either at the district court or on appeal, has argued that the fees charged to the concessionaires are too high. The concessionaires are not parties to this action. The ordinances in question do not even apply to most of them.2 Moreover, no one has argued, and there is no evidence in the record, that the total price charged to airline passengers is unreasonable. Second, the issue of monopoly was barely mentioned by the parties below and on appeal.3 The focus of the airlines’ argument as to the unreasonableness of the fees was that costs and revenues were allocated improperly in setting the user fees. Third, and most significant, the approach taken by the majority does not address the issue of whether the costs allocated, and thus the fees charged, to the airlines are unreasonable. The majority finds the existence of a monopoly price because the rent charged to the concessionaires is more than three times the costs attributed to them under the Airport Authority’s cost allocation method. This approach, however, assumes the very issue that we have been asked to decide — -whether the costs were correctly allocated. If a larger percentage of the costs of the airport properly should have been allocated to the concessionaires, then the disparity between the rent and the costs would not be as great. The issue in this case is whether various federal and state laws prohibit the cost accounting method employed by the airport in setting the user fees charged to the airlines. I deem it appropriate to restrict a federal court’s involvement with a municipal corporation’s method of setting rates for the use of its property — for reasons of comity and judicial restraint — to the specific issues that are brought before the court.
Moreover, I believe that the majority opinion inappropriately relies on a statute that is unnecessary to its decision. The airlines challenge the ordinances on the basis of three statutes: section 18(a)(1) of the Airport and Airway Development Act of 1970, as amended, 49 U.S.C. § 1718(a)(1) *1274[now codified at 49 U.S.C. § 2210(a)(1) (Supp.1982) ]; the Federal Anti-Head Tax Act, 49 U.S.C. § 1513 (Supp. IV 1980) (prior to 1982 amendment); and section 8-22-3-11(9) of the Indiana Airport Authorities Act, Ind.Code Ann. §§ 8-22-3-1 to -35 (West 1982). All three statutes require the airport to charge “reasonable” fees. As the majority correctly notes, we need not decide whether the airlines have standing to raise the Airport and Airway Development Act of 1970. Because I would hold that the ordinances violate the Indiana statute, and because the federal Anti-Head Tax Act poses difficult and unresolved problems of interpretation, I would not and do not reach the question of whether the ordinances also violate the federal statute.4 Thus, we need not decide whether “reasonable” under the Act means the same thing as it does under the Indiana statute.5 Furthermore, section 1513(b) clearly applies only to fees charged to “aircraft operators.” It does not apply to fees charged to concessionaires. The majority opinion thus has expanded the reach of the statute and created regulation of the market system where Congress clearly had no intent to regulate.
Finally, I see no need to discuss potential means of reducing airport congestion through rate-making methodology. Courts are not experts on the subject of airport management and financing. The parties have not asked for our advice on airport congestion.6 The parties have not argued before this court that congestion is, or is even likely to be, a problem at Indianapolis International Airport. Until this matter is squarely presented to us as an issue necessary to a decision, we should not address it.
II
Prior to September 1, 1980, the Airport Authority’s charges to the airlines were set through leases negotiated with the airlines. In determining the fees to be charged, the Airport Authority totalled its operating and maintenance expenses plus the cost of its debt service and subtracted all revenues from airport users other than the airlines. The Airport Authority then set its fees in an amount sufficient to recover from the airlines the balance of the amount necessary to pay its expenses and debt service. Before the lease expired on August 31, 1980, the parties attempted to negotiate a new lease but were unable to do so. In August 1980, the Airport Authority passed ordinance 4-1980, which established fees and charges effective September 1, 1980. In December 1980, the Airport Authority passed ordinance 5-1980, which established fees and charges effective February 1, 1981.
In determining the fees to be set by the ordinances, the Authority relied on accounting reports prepared by its staff and the firm of Crenshaw & Associates (“Crenshaw Report”). The Crenshaw Report divided the airport into various cost centers. There were two types of cost centers: revenue-producing and nonrevenue-producing. Costs were then allocated among the cost centers. Costs from each revenue-producing cost center were charged to that specific center. Costs from nonrevenue-producing cost centers were allocated among rev*1275enue-producing cost centers using one of two methods: management analysis or revenue acres. Under the management analysis method, airport management determined what percentage of the costs benefitted the users of éach revenue-producing cost center and then allocated the costs accordingly. Under the revenue acres method, costs were allocated strictly according to the space occupied by each revenue-producing cost center.
Costs were then allocated among the users of each revenue-producing cost center. The concessionaires were considered to be users only of the terminal building cost center, and thus they were allocated costs solely from that cost center. The parking lot was considered to be a user only of the parking lot cost center, and thus it was allocated costs solely from that cost center. Users were divided into two classes: aeronautical and nonaeronautical. Aeronautical users were charged at a rate to recover the costs attributed to them. Nonaeronautical users were charged market rates, with their attributed costs serving as a minimum.
In determining how to assess fees against aeronautical users, the Airport Authority divided the users into classes. Commercial airline users’ fees were assessed through rental and landing fees. General aviation users’ fees were assessed through a fuel flowage fee. That fee had not been raised since 1971. The costs allocated to general aviation totalled over $400,000. The fuel flowage fee recovered approximately $250,000.
The ordinances increased the rates charged to the airlines. Under the lease, the airlines paid $.46 per thousand pounds gross landing weight and $17.55 per square foot for rent in the terminal. Under ordinance 4-1980, the airlines were to pay $.6015 per thousand pounds gross landing weight and $21.95 per square foot in rent. Under ordinance 5-1980, the landing fee was increased to $.6771 per thousand pounds gross landing weight. Under the ordinances, the airport was budgeted to have net income of $2,917,129 for 1981. After September 1, 1980, the airlines continued to pay both rent and landing fees at the rates imposed under the expired leases.
The district court, following a bench trial, ruled that the rates and charges established by the ordinances were unreasonable because the Airport Authority’s method of allocating costs and revenues failed to recognize interdependencies between aeronautical and nonaeronautical users. The court further held that the rates discriminated against the airlines and in favor of general aviation.7 Finally, the court held that the airlines were holdover tenants under Indiana law, and as such, the Airport Authority by accepting rent from them had waived its right to the rent imposed by the ordinances.
On appeal, the Airport Authority argues that the district court erred in holding that its rates and fees under the ordinances were unreasonable. It contends that the district court’s opinion improperly forces it to use revenues from nonaeronautical users to subsidize the airlines. The Airport Authority argues that it has broad discretion in adopting its rate-making methodology. It further maintains that the general aviation flowage fees were not discriminatory, because it can use different methods to collect fees from different classes of users.
The airlines argue that the district court properly found that the accounting method was improper and that the Airport Authority misapplied its own improper methodology. They argue that the general aviation fee was discriminatory because it failed to recover the costs attributable to general aviation.
*1276III
The Indiana Airport Authorities Act provides that an airport authority board “may do all acts necessary or reasonably incident to carrying out the purposes of this chapter, including the following: ... To adopt a schedule of reasonable charges and to collect them from all users of facilities and services within the district ...” Ind.Code Ann. § 8-22-3-11(9) (West 1982). Under the statute, a reasonable charge is one that reflects the differences in the extent of use of airport facilities by different classes of users. Evansville-Vanderburgh Airport Authority District v. Delta Air Lines, Inc., 259 Ind. 464, 467, 288 N.E.2d 136, 137 (1972). As the court noted, “The very concept of a user fee implies that there are different uses that can be identified and the amount of the fee charged must relate to that use.” Id., 288 N.E.2d at 137. Thus, the amount of the fee charged must relate to the benefits supplied to the user, measured according to the costs incurred in supplying the benefits.8
This conclusion has two important corollaries. First, the fee charged to one user cannot relate to costs incurred in supplying benefits to those other than that user. Second, each user or class of users must bear its full share of the costs of its benefits. Violation of either principle would lead to a fee that is unreasonable under Indiana law.
Applying these principles, I find that, as a matter of law, the rates imposed by the ordinances are unreasonable. First, the fees charged to the airlines reflect the cost of benefits fairly attributable to other users of the airport. Second, the fees fail to reflect the extent of use by the users.
One benefit not reflected in the fees charged to the concessionaires is the production of customers for the parking lot and concessions. The parties agree that the' persons using the airport parking lot and concessions are airline passengers. Thus, there is a dependence on the airlines by the concessionaire users. Cf. Raleigh-Durham Airport Authority v. Delta Air Lines, Inc., 429 F.Supp. 1069, 1083 (E.D.N.C.1976) (“[t]he authority is directly dependent on the inflow and outflow of commercial passengers and freight, as served by the airlines, to provide the people — traffic who use a majority of such services as restaurant, parking space, ticket counter, concessions, etc.”). Daniel C. Orcutt, Executive Director of the airport, testified that “[t]he airport provides an economic opportunity for these companies to conduct their business, and they are willing to pay more than the cost for that opportunity, to have the exposure to the traffic.” Transcript at 208. The dependence of the nonaeronautical users on the airlines to produce customers means that those users receive a substantial benefit from the airlines. The costs of producing that benefit, however, are borne entirely by the airlines. Under the Indiana statute, that is unreasonable.9 There was testimony at the trial about several different cost accounting methods that the Airport Authority could use to recognize that dependency, such as the by-product and joint-product methods. It is, of course, unnecessary for this court or the district court to endorse any particular method.
Second, the fuel flowage fee charged to general aviation users did not recover the costs allocated to general aviation. The *1277statute requires that the fee be related to the costs of the services provided and be determined according to the extent of the use. The fee charged here fails to meet that standard, and thus it is unreasonable. However, nothing in the statute requires that all users be assessed according to the same formula or that costs be collected in the same manner. The Airport Authority-may collect fees from general aviation through a fuel flowage fee rather than through a landing fee; but however it chooses to collect its fee, that fee must recover the costs properly allocable to that user.
Third, the Airport Authority, in determining its cost centers, included in the landing area cost center both land that was not part of the clear zone for any existing runway and land that was at that time not even owned by the airport.10 This had the effect of increasing the size of the landing area cost center and thus of the amount allocated to that cost center under the revenue acres method. The users of that cost center — the commercial airlines — were thus charged with costs that had no relation to the extent of their use of the airport. This is unreasonable.11
The airport firefighting costs were allocated according to management analysis. Although the majority of the firefighting activity took place in the terminal building, most of the costs were allocated to the airfield. The Airport Authority argues that this is because the firefighting equipment and personnel are required in case there is a major aircraft disaster, not to deal with the minor emergencies that occur in the terminal building. This analysis is reasonable under the statute, because it relates the costs to the extent of the use.
IV
Both in the district court and on appeal, the Airport Authority has characterized the dispute over cost accounting methods as a choice between the “single cash register method” and the “multiple cash register method.” In the former, the airport is treated as one cost center and revenues from the nonaeronautical users are applied to lower the fees charged to the airlines. In the latter, the airport is treated as a series of cost centers, each of which must stand alone for rate-making purposes. The Airport Authority contends that the district court opinion would force it to apply the single cash register method. I do not understand the district court opinion to require this, and I would not so hold. The Indianapolis Airport Authority may establish as many cost centers as it deems prudent; but it must allocate the costs among them, and among the users of a cost center, fairly. See Raleigh-Durham Airport Authority v. Delta Air Lines, Inc., 429 F.Supp. at 1079 (a multiple cash register system is a reasonable method of allocating costs if it is fairly and regularly applied).
Requiring the Airport Authority to consider dependencies in allocating costs does not violate the rule of public utility rate-making that revenues from unregulated activities cannot be used to subsidize regulated activities. See Smyth v. Ames, 169 U.S. 466, 18 S.Ct. 418, 42 L.Ed. 819 (1898). Instead, it merely requires a fair allocation of costs in determining the revenues of the activities. Moreover, under the Indiana statute the fees charged to concessionaires are regulated. The Indiana Supreme Court has recognized that concessions are “users” of an airport within the meaning of section 8-22-3-11(9). Evansville-Vanderburgh Airport Authority District v. Delta *1278Air Lines, Inc., 259 Ind. at 466-67, 288 N.E.2d at 137.
V
Because I agree with the majority opinion that the airlines were not holdover tenants under Indiana law, I also agree that the case must be remanded to the district court for further proceedings.
. In addition to the Indianapolis International Airport, the Indianapolis Airport Authority operates four "reliever" general aviation airports. The fees charged at those airports are not at issue here.
. The ordinances impose fees for: certain ground transportation concessions, namely buses, taxis and courtesy vehicles; the observation deck; mobile catering truck operators; and public and employee parking lots. It should be noted that the parking lots are not true "concessions,” as they are owned and operated by the Airport Authority. However, because the lots are a source of nonaeronautical revenue, they are treated as though they were a concession.
. In a voluminous trial court record (consisting of over 800 pages of pleadings and over 1,100 pages of transcript), I could find only a handful of references to an argument that the airport has a monopoly. The balance of the record focused on the question of allocation of costs and revenues. Similarly, on appeal, there was no mention of monopoly in the parties’ briefs. Moreover, the statistics cited by the majority to prove the airport's monopoly are not contained in the record before us.
. In Raleigh-Durham Airport Authority v. Delta Air Lines, Inc., 429 F.Supp. 1069 (E.D.N.C.1976), a case raising the issue of the reasonableness of airport user fees, the court based its decision solely on a state statute requiring reasonable charges.
. Whether "reasonable" means the same thing under the Anti-Head Tax Act as it docs under the Indiana statute is open to question. As discussed infra, a reasonable charge under the Indiana statute is one that reflects the extent of use of airport facilities by a user. Thus, the allocation of costs among users is a component of reasonableness. Arguably, the federal statute mcrely restricts the airport’s overall profit, while not imposing any restrictions on from whom costs may be recovered. See Note, Airline Deregulation and Airport Regulation, 93 Yale L.J. 319, 324 n. 35 (1983). See also Island Aviation, Inc. v. Guam Airport Authority, 562 F.Supp. 951, 959-60 (D.Guam 1982) (reasonable fee under § 1513(b) is one that reflects actual costs of facilities and is designed to make airport as self-sustaining as possible).
. The impact of rate-making on airport congestion was raised in the Brief of Various Public Airport Authorities, Amici Curiae at 13-16.
. The district court relied in part on both federal statutes in reaching its conclusions. This does not preclude this court from basing its decision solely on the Indiana statute. This court may affirm a district court's conclusions on grounds other than those relied upon by the lower court where the district court used incorrect reasoning. Beach v. Owens-Coming Fiberglas Corp., 728 F.2d 407, 408 n. 1 (7th Cir.1984).
. The measurement is the cost of the benefit supplied, not the value of the benefit. Courts are ill-equipped to determine the value of particular benefits accorded to airport users. See American Airlines, Inc. v. Massachusetts Port Authority, 560 F.2d 1036, 1038 (1st Cir.1977).
. For example, in the airport terminal building cost center, the total cost attributable to the cost center was calculated. It was then allocated among the users (the various airlines and the various concessions) according to square footage occupied by each user. Thus, the rental charge to the concession users ignores the costs of producing the customer flow. Similarly, the Airport Authority treated the passenger parking lot as a separate cost center. Thus, the only costs allocated to it were the direct costs of operating the parking lot and a percentage of indirect costs allocated under the revenue acres and management analysis methods. The parking lot cost center was not charged with any of the costs of producing its own customers.
. The Airport Authority included land that will be in the clear zone of a future runway and land currently in a trailer park that the Airport Authority has been trying to acquire for several years. The parties have not informed this court of the current status of the acquisition efforts.
. The district court, in its opinion, found the inclusion of land unreasonable because it resulted in prefunding of capital expenditures. It is clear from the record that the Airport Authority was not seeking to prefund the capital expenditures; no costs for acquisition or construction of a future runway or purchase of the trailer park were included in the rate base. However, its inclusion of the land in the cost center may still be found unreasonable on different grounds. See supra note 7.