CHIEF JUSTICE VOLLACK delivered the Opinion of the Court.

We granted certiorari to review the court of appeals decision in Arapahoe County Public Airport Authority v. Centennial Express Airlines, Inc., 942 P.2d 1270 (Colo.App. 1996), to determine whether the court of appeals erred in reversing a permanent injunction entered in favor of the plaintiff, Arapahoe County Public Airport Authority (the Authority), prohibiting the defendant, Centennial Express Airlines, Inc., and its wholly owned subsidiary, Golden Eagle Charters, Inc., d/b/a Centennial Express Airways, Inc. (Centennial Express), from conducting scheduled air carrier service in and out of Centennial Airport (Centennial). We reverse.

I.

Centennial was built in 1967 to serve the growing aviation needs of the Denver metropolitan region and has since become one of the largest and busiest general aviation facilities in the country. Centennial is located fourteen miles southeast of downtown Denver and sits on approximately 1,200 acres of land in Arapahoe and Douglas Counties. In 1975, Arapahoe County established the Authority pursuant to the Public Airport Authority Law, sections 41-3-101 to -108, 17 C.R.S. (1973), to own and operate Centennial as a political subdivision of the State. The Authority owns all of the land and facilities at Centennial except for two runways which it leases from Arapahoe County.

To fund airport construction and operations, the Authority has accepted approximately $30.1 million in federal grants. As a condition to accepting these grants and pursuant to federal law, the Authority has given its assurance that it "will make its airport available as an airport for public use on fair and reasonable terms and without unjust discrimination, to all types, kinds, and classes of aeronautical uses." A separate assurance provides that the Authority "may prohibit or limit any given type, kind, or class of aeronautical use of the airport if such action is necessary for the safe operation of the airport or necessary to serve the civil aviation needs of the public."

Local, regional, and national planning schemes designate Centennial as a general aviation reliever airport for Denver's primary air carrier airports, Stapleton International (Stapleton), which closed in February of 1995 and Denver International (DIA), which opened upon Stapleton's closure. Locally, resolutions passed by the Board of County Commissioners of Arapahoe County in 1966 approved funding for the construction of a general aviation airport. Newspaper accounts of open meetings held following this funding approval indicate that county officials hoped to lure new industry and expand the county's tax base by building an airport to "serve general aviation, not scheduled carriers or military planes." A new airport would also ease general aviation overcrowding at Stapleton. In one news report, the Federal Aviation Administration (FAA) area director proclaimed that the airport was "a much needed reliever terminal for general aviation."

Regionally, the Denver Regional Council of Governments (DRCOG), a planning organization of county and municipal governments, has adopted several aviation plans that guide the development and operation of airports in the Denver area. Specifically, the 2010 Regional Aviation System Plan (2010 Plan), which was published by DRCOG in 1989, provides that Stapleton is the only commercial air carrier airport in the region and designates Centennial "as a non-commercial passenger, transport-category, general aviation reliever airport." Similarly, the Regional Aviation System Planning Program Data File, which was published by DRCOG in 1991, provides that Stapleton is the "air carrier facility for the Denver region" and categorizes Centennial "as a non-commercial passenger, transport category, G.A. reliever."

Nationally, the National Plan of Integrated Airport Systems (NPIAS), which was presented to Congress by the Secretary of Transportation in 1991, does not include Centennial in its summary of Colorado's primary and commercial service airports. Instead, the NPIAS lists Centennial as a reliever airport intended to alleviate general aviation congestion at Denver's primary commercial airport through 1999.

Due to its planned role as a general aviation reliever and strong opposition from citizens who live near the airport, scheduled passenger service has never been authorized at Centennial. While fixed-base air taxi and charter flights are permitted, Centennial's master plan, which was published in 1981, provides that air taxi, charter flights, and military use constitute less than one percent of the airport's total operations. Because scheduled passenger service has never been permitted, Centennial presently operates without a terminal, baggage system, or passenger security system.

Despite Centennial's lack of facilities, private efforts have been made to bring scheduled passenger service to the airport. In response, the Authority has increased efforts to prohibit scheduled passenger service. On July 21, 1993, the Authority sent a letter to the United States Department of Transportation (USDOT) asserting that the Authority did not have to approve applications for scheduled passenger service and asking USDOT for its opinion on the issue. On September 4, 1993, the Authority also amended the "Minimum Standards for Commercial Aeronautical Activities" (the Standards) governing operations at Centennial. These Standards now define "Airport Purpose" as

any Authority action, undertaking or development that is consistent in maintaining the non-certificated status of the Airport and in preserving the Airport funding category as a "Reliever Airport" serving general aviation users. Under no circumstances shall the Airport Purpose include scheduled passenger services.

(Emphasis added.)

On December 20, 1994, Centennial Express began scheduled passenger service out of Centennial to Dalhart, Texas. Centennial Express has a valid air carrier certificate issued by the FAA. At the time of its maiden flight, Centennial Express was aware of the Authority's ban on scheduled passenger service but chose to delay notifying the Authority until the return flight from Dalhart. Centennial Express also issued a press release announcing that it would soon provide scheduled passenger service from Centennial to Amarillo, Colorado Springs, Grand Junction, and other Western Slope airports in 1995. Additionally, Centennial Express planned to begin regular jet flights from Colorado Springs to Chicago, Kansas City, Houston, Dallas, Phoenix, Los Angeles, San Francisco, and Seattle.

The following day, the Authority filed suit in Arapahoe County District Court (the district court) seeking a temporary restraining order and preliminary and permanent injunctions preventing Centennial Express from conducting scheduled passenger service out of Centennial. On December 22, 1994, the district court granted the Authority's request for a temporary restraining order, concluding in part that

[r]eal, immediate, and irreparable injury may be prevented if [Centennial Express is] enjoined from conducting and expanding illegal scheduled passenger service at the Airport. [Centennial Express has] made a unilateral decision to conduct illegal scheduled passenger service at the Airport. [Centennial Express has] flaunted the law by disregarding the Airport's Minimum Standards. [The Authority] manages the Airport. Indeed, [the Authority's] reason to exist turns on its ability to govern and manage the Airport. If the requested relief is not provided, [the Authority] will be stripped of its ability and authority to manage the Airport.

On December 23, 1994, more than seventeen months after the Authority's initial request, USDOT responded to the Authority's letter as to whether it could ban scheduled passenger service at Centennial. In relevant part, the USDOT's letter provides as follows:

In addressing similar cases in the past, FAA has found it arbitrary to exclude any particular class of service due to factors that are not related to the impacts of that service.

Although the material that [the Authority] submitted states that approval of scheduled service would increase the number of operations and passengers at Centennial Airport, there was insufficient information submitted with [the Authority's] letter to demonstrate that a restriction of any particular category of operation could be adequately supported. For example, although individual factors are not alone likely to be dispositive, [the Authority's] letter does not discuss the nature and extent of any resulting environmental impact, congestion, or effect on airport facilities such as the terminal or parking, that would result from the initiation of scheduled service.

Later, the opinion letter states that the Authority's letter also raises a policy issue relating to how to harmonize several important goals — allowing the citizens of a region to plan and manage their aviation resources on a regional basis, while at the same time preserving and enhancing the performance of the national aviation system and ensuring that statutory and regulatory requirements associated with use of federal grant funds are not violated. . . . We firmly support regional planning and decision-making and strongly believe that local governments should, wherever possible, plan, develop and operate their transportation systems in an integrated and regional context, consistent with applicable federal law. . . .

[W]here the volume of air traffic is approaching or exceeding the maximum practical capacity of an airport, an airport owner may designate a certain airport in a multiple airport system (under the same ownership and serving the same community) for use by a particular class of aircraft so long as the owner can assure that all classes of aeronautical needs can be fully accommodated within the system of airports under the owner's control. . . .

The issue that this raises is whether [USDOT] should change its policy to extend the flexibility now afforded to multiple airports under joint ownership to individually-owned multiple airports which are planned and operated under a regional agreement. . . . Because this would be a significant policy change, full consideration by the public and the aviation community is warranted. Therefore, we will be initiating, early next year, a process to obtain a full range of views on this issue.

On January 10, 1995, after conducting several hearings, the district court entered a permanent injunction prohibiting Centennial Express from conducting scheduled passenger service out of Centennial. Centennial Express appealed and also filed a complaint with the Federal Aviation Administration (FAA). The court of appeals reversed the district court's ruling, concluding that the Authority's regulation prohibiting scheduled passenger service was preempted by 49 U.S.C. § 41713(b)(1) (1994). The court of appeals also held that the district court should have left the question of whether the Authority could prohibit scheduled passenger service to the federal administrative agencies' primary jurisdiction.

II.

At the outset, we must determine whether this court should defer to the federal agencies' holding concurrent jurisdiction over this case. The doctrine of primary jurisdiction, or the deference doctrine, calls for judicial deference in cases involving technical questions of fact uniquely within an agency's expertise and experience, or in cases where uniformity and consistency require administrative discretion. See Nader v. Allegheny Airlines, Inc., 426 U.S. 290, 303-04 (1976); Columbia Gas Transmission Corp. v. Allied Chem. Corp., 652 F.2d 503, 519 n. 14 (5th Cir. 1981); Great Western Sugar Co. v. Northern Natural Gas Co., 661 P.2d 684, 690 (Colo.App. 1982). No fixed formula exists for deciding when to invoke this doctrine, but it should be utilized reluctantly where the issue is strictly a legal one that is within the conventional competence of the courts. See Great Western Sugar, 661 P.2d at 690.

The issues in this case do not involve complex questions of fact. Rather, we have been asked to consider whether the district court properly enjoined Centennial Express from conducting scheduled passenger service out of Centennial. As defenses, Centennial Express claims that (1) the Authority's regulation prohibiting scheduled passenger service at Centennial is preempted by federal law and (2) the ban on scheduled passenger service violates the terms of the Authority's federal grant assurances. In our view, these legal and interpretive questions do not "go beyond the understanding of judges" or lay "at the heart of the task assigned the agency by Congress." See Mashpee Tribe v. New Seabury Corp., 592 F.2d 575, 580-81 (1st Cir. 1979).

Additionally, the FAA has yet to rule on either of the complaints despite the fact that they were filed more than three years ago. Similarly, although the USDOT opinion letter alludes to "initiating, early [in 1995], a process to obtain a full range of views on" its policy regarding individual airport participation in regional airport planning, we have no indication from the parties or USDOT that such efforts have begun. Because there is a strong public interest in resolving this case promptly, we refuse to defer to administrative action which is of "uncertain aid and uncertain speed." See id. at 581.

Centennial Express also points to the USDOT opinion letter in arguing that deference is warranted in this case. In Banner Advertising, Inc. v. People, 868 P.2d 1077, 1083 (Colo. 1994), we addressed the level of deference we must afford an opinion letter issued by the FAA. Specifically, we explained:

[T]he opinion of the FAA's chief counsel . . . was not reached as a result of hearing adversary proceedings in which he found facts and reached conclusions of law. It is in no way binding on a court. Nevertheless, the letter was written as part of the official duties of the chief counsel, and is based on a level of more specialized expertise than most judges possess, so we may properly look to it for guidance. While opinion letters from administrative agencies are not binding authority, they can be used as persuasive authority.

Id. Contrary to Banner, where we chose to defer to the agency's letter, we believe the USDOT's opinion letter in this case does not require deference. First, the letter is brief, contains no federal preemption analysis, and fails to cite any federal cases for its propositions. Second, the letter is inconclusive because it states that the Authority submitted "insufficient information" on the impact scheduled passenger service would have at Centennial. Third, because the opinion letter is only persuasive authority, it is not binding on this court. See id.

In this case, Centennial Express began scheduled passenger service in clear defiance of the Authority's regulations, before the USDOT's opinion letter was issued, and before filing its FAA complaint. Nevertheless, Centennial Express asserts that even though it has disregarded valid regulations passed pursuant to state law, we must defer to the federal agencies' concurrent jurisdiction. We disagree. If we defer to the federal agencies, we would affirm Centennial Express's course of conduct and foreclose the Authority's only avenue of relief. This would allow future airport users to unilaterally conduct and continue operations in violation of airport rules so long as they implicate federal jurisdiction in some way. Under these circumstances, we refuse to defer to the federal agencies' concurrent jurisdiction.

III.

Centennial Express argues that the ban on scheduled passenger service is preempted by federal law. We disagree.

Congress radically altered the character of commercial aviation when it amended the Federal Aviation Act and deregulated the airline industry pursuant to the Airline Deregulation Act of 1978 (ADA). See Pub.L. 95-504, 92 Stat. 1705. In so doing, Congress determined that market forces were better suited for promoting efficiency, innovation, low prices, variety, and quality in the air transportation industry. See Morales v. Trans World Airlines, Inc., 504 U.S. 374, 378 (1992). However, the absence of federal regulation caused concern in Congress that individual states would pass inconsistent and conflicting laws regulating the airline industry. See H.R. Rep. 95-1211, at 15-16 (1978) reprinted in 1978 U.S.C.C.A.N. 3737, 3752; see also Margolis v. United Airlines, Inc., 811 F. Supp. 318, 320-21 (E.D. Mich. 1993). Consequently, the ADA included a provision that preempted all state laws relating to the rates, routes, or services of an interstate air carrier. See 49 U.S.C. § 1305(a)(1) (Supp. III 1979). Currently, 49 U.S.C. § 41713(b)(1) (the ADA preemption provision) provides that a political subdivision of a state "may not enact or enforce a law, regulation, or other provision having the force and effect of law related to a price, route, or service of an air carrier."

Two cases from the United States Supreme Court offer guidance on the scope of the ADA preemption provision. In Morales, several airlines filed suit against the State of Texas seeking injunctive relief prohibiting enforcement of state regulations pertaining to airline fare advertising. The airlines argued that the regulations were preempted by the ADA preemption provision. Relying upon cases in which the Supreme Court interpreted a similarly worded preemption provision in the Employee Retirement Income Security Act of 1974 (ERISA), the Court determined that the ADA preemption provision expressed a broad preemptive purpose that included all "State enforcement actions having a connection with or reference to airline rates, routes, or services." Morales, 504 U.S. at 383-84; see also American Airlines, Inc. v. Wolens, 513 U.S. 219, 223 (1995). The Morales Court noted, however, that preemption was inappropriate where the state action affects airline rates, routes, and services "in too tenuous, remote, or peripheral a manner." See Morales, 504 U.S. at 390; Wolens, 513 U.S. at 224.

In New York State Conference of Blue Cross Blue Shield Plans v. Travelers Insurance Co., 514 U.S. 645, 654-56 115 S.Ct. 1671, 1676-77, 131 L.Ed.2d 695 (1995), the Supreme Court explained that it may have interpreted the "relate to" language in prior ERISA cases too broadly. Specifically, the Court explained:

If "relate to" were taken to extend to the furthest stretch of its indeterminacy, then for all practical purposes pre-emption would never run its course, for really, universally, relations stop nowhere. But that, of course, would be to read Congress's words of limitation as mere sham, and to read the presumption against pre-emption out of the law whenever Congress speaks to the matter with generality. That said, we have to recognize that our prior attempt to construe the phrase "relate to" does not give us much help drawing the line here.

Id. at 655 (citation and internal quotation marks omitted). Instead, the Court explained that it must address ERISA preemption cases "with the starting presumption that Congress does not intend to supplant state law." Id. at 654. With this presumption in mind, the Court then explained that it "simply must go beyond the unhelpful text and the frustrating difficulty of defining its key term, and look instead to the objectives of the ERISA statute as a guide to the scope of the state law that Congress understood would survive." Id. at 656.

Despite the broad reach the Morales Court gave the ADA preemption provision, the Travelers decision establishes a less literal method for determining whether state regulations concerning aviation are preempted. Specifically, Travelers counsels that we should first presume "that Congress does not intend to supplant state law." Id. at 654. Then, we must review the objectives of the statute in defining "the scope of the state law that Congress understood would survive." Id. at 656.

Turning to the facts of this case, we believe that the Authority's ban on scheduled passenger service is not preempted. Because the regulation concerns an area of local and regional planning, it will not lead to inconsistent or conflicting state regulations. Therefore, the regulation does not undermine the purpose of the ADA preemption provision.

The Authority's regulatory ban on scheduled service also survives scrutiny under the plain meaning of the ADA preemption provision because it does not regulate the manner in which airport users conduct their business. We disagree with the court of appeals that prohibiting scheduled passenger service "relates to" airline services because it does not concern typical service-oriented tasks such as ticketing, boarding procedures, providing meals and drinks to passengers, and baggage handling. See Hodges v. Delta Airlines, Inc., 44 F.3d 334, 336 (5th Cir. 1995). Similarly, the Authority is not regulating airline fares or routes because the ban on scheduled service does not delineate what airlines can charge or where they can fly.

While Centennial Express has raised preemption as a defense to the Authority's ban on scheduled passenger service, we believe the Authority's actions more appropriately fall under 49 U.S.C. § 41713(b)(3) (1994) (the proprietor's exception), which provides conclusive support for the Authority's position. That section provides that the ADA preemption provision does not limit a political subdivision that owns or operates an airport "from carrying out its proprietary powers and rights."

Federal courts have considered the scope of the proprietor's exception in two significant areas of airport management. The first, and most extensive, of these areas concerns an airport proprietor's ability to regulate airport noise. These cases hold that because they may be held liable for excessive noise, airport proprietors may restrict aircraft operations to accommodate permissible noise levels under the proprietor's exception. See City of Burbank v. Lockheed Air Terminal, Inc., 411 U.S. 624, 635-36 n. 14 (1973); Santa Monica Airport Ass'n v. City of Santa Monica, 659 F.2d 100, 104 (9th Cir. 1981); British Airways Bd. v. Port Auth. of New York, 558 F.2d 75, 84 (2d Cir. 1977).

The second area of airport management that has been deemed to fall under the proprietor's control are perimeter rules, which restrict a commercial flight's maximum radius in order to limit an airport's ground congestion and divert long-haul traffic to other regional airports. See City of Houston v. Federal Aviation Admin., 679 F.2d 1184, 1196 (5th Cir. 1982); Western Air Lines, Inc. v. Port Auth. of New York New Jersey, 658 F. Supp. 952, 958 (S.D.N.Y. 1986), aff'd, 817 F.2d 222 (2d Cir. 1987). In contrast to cases affirming noise restrictions, these cases uphold perimeter rules even though they have no relationship to an airport's liability exposure. As one of these courts has reasoned,

although questions of permissible noise regulation predominate in the courts, other proprietor-imposed regulations are presently accepted as valid exercises of proprietary powers. A proprietor's interest in regulating ground congestion at its airports would appear to be at the core of the proprietor's function as airport manager, perhaps even more so than the regulation of noise; and the ability of a proprietor . . . to allocate air traffic in its three airport system is important to the advancement of this interest.

Western Air Lines, 658 F. Supp. at 957 (internal quotation marks omitted).

There are no cases that address the specific question posed by the present case. Nevertheless, we believe that an airport proprietor's ban on scheduled passenger service falls squarely within the proprietor's exception. While regulations concerning aircraft noise and ground congestion restrict the manner in which airport users conduct their operations, a ban on scheduled service seeks to accomplish a more fundamental goal in setting the boundaries of permissible operations at the airport. The power to control an airport's size exists at the core of the proprietor's function and is especially strong where, as here, the prohibited use has never been allowed, or even contemplated. See id.; see also Montauk-Caribbean Airways, Inc. v. Hope, 784 F.2d 91, 97 (2d Cir. 1986) (finding that, under the proprietor's exception, a municipality could prevent a seasonal operator from expanding its operations to include year-round service).

By unilaterally commencing scheduled passenger service out of Centennial, Centennial Express has essentially proclaimed that the Authority, a political subdivision of the state, lacks the power to define and limit the scope of permissible operations at its airport. However, Colorado law clearly gives the Authority this power. See 41-3-106(1)(h), 11 C.R.S. (1997). Accordingly, the Authority's ban on scheduled passenger service is a valid exercise of its proprietary powers that is not preempted by federal law.

IV.

Centennial Express also argues that the Authority has violated the terms of the federal grant assurances under which it has agreed to "make its airport available as an airport for public use on fair and reasonable terms and without unjust discrimination, to all types, kinds, and classes of aeronautical uses." See 49 U.S.C. § 47107(a) (1994) (providing that project grant application may be approved only if Secretary of Transportation receives satisfactory written assurances). We disagree.

While the grant assurances prohibit discrimination among different types, kinds, and classes of aeronautical uses, we refuse to construe them so broadly that airport proprietors must accommodate every possible aeronautical use. By the terms of the assurances, an airport proprietor who has accepted federal funding must make its airport available on "fair and reasonable terms without unjust discrimination." The anti-discrimination provision therefore prohibits airport owners from using their proprietary power to grant one operator access while denying access to, or imposing unfair terms on, a similarly situated operator. Here, the Authority is not discriminating against a particular operator because the ban on scheduled passenger service applies to all airport users equally.

Furthermore, a separate assurance allows airport proprietors to prohibit specific aeronautical uses "if such action is necessary for the safe operation of the airport or necessary to service the civil aviation needs of the public." The Authority's ban on scheduled passenger service is necessary to ensure the safe operation of the airport. Although it initially plans to operate on a small scale, Centennial Express has ambitions to become much larger. Opening Centennial's doors to Centennial Express would also require the Authority to make Centennial available to other airlines who wish to provide scheduled passenger service. See 49 U.S.C. § 47107(4) (1994). These new operators, some of whom may find conditions at Centennial more appealing than DIA, promise to bring increased aviation traffic to an already congested airport. This increased congestion is sure to have an impact on airport safety. Increased passenger traffic also requires additional facilities such as a terminal, security and baggage systems, which are currently lacking at Centennial. Without these facilities, the airport would become unsafe for passenger use.

Local, regional, and national aviation planning also strongly indicates that the aviation needs of the public are better served if Centennial continues to function as a general aviation reliever airport. The sudden imposition of scheduled passenger service and a resulting increase in commercial operations at Centennial would disrupt this planning scheme and force general aviation operators out of this valuable reliever airport. See 49 U.S.C. § 47102(18) (1994) (defining a "reliever airport" in part as an airport designated "to provide more general aviation access to the overall community"). Currently, Centennial is congested and accommodates the majority of the region's general aviation demand while DIA continues to operate well below capacity. A shift in commercial operations from DIA to Centennial would result in more of a disparity in the allocation of aircraft operations among the region's airports. See City of Houston, 679 F.2d at 1191.

The Authority's regulation prohibiting scheduled passenger service does not discriminate against individual airport users. Furthermore, the ban on scheduled passenger service "is necessary for the safe operation of the airport" and services "the civil aviation needs of the public." For these reasons, the Authority has not violated the terms of the federal grant assurances.

V.

The Authority, as the owner and operator of Centennial, has the power to enact regulations which prohibit scheduled passenger service at its airport. This regulatory ban is not preempted by federal law and does not violate the terms of grant assurances that the Authority has given to the federal government. We therefore hold that the district court properly enjoined Centennial Express from conducting scheduled passenger service out of Centennial. Accordingly, we reverse the court of appeals and remand with directions to reinstate the district court's order.

JUSTICE SCOTT concurs and specially concurs.

JUSTICE BENDER dissents, and JUSTICE MARTINEZ joins in the dissent.

JUSTICE HOBBS does not participate.