On April 27, 2018, the House of Representatives passed the FAA Reauthorization Act of 2018 ( H.R. 4 ), a measure to reauthorize federal civil aviation programs, including the Federal Aviation Administration (FAA), for a six-year period. H.R. 4 does not include a controversial proposal to privatize air traffic control (ATC) laid out in an earlier bill, H.R. 2997 . On May 9, 2018, the Senate Committee on Commerce, Science, and Transportation reported a four-year FAA reauthorization bill ( S. 1405 , S.Rept. 115-243 ) that does not address ATC privatization. Despite many similarities, there are a number of differences in the two bills, including the length of authorization, funding amounts, and other provisions. If either bill is enacted, it would be the first long-term FAA reauthorization act since the FAA Modernization and Reform Act of 2012 ( P.L. 112-95 ) expired at the end of FY2015. Disagreement regarding ATC reforms has stalled action on a subsequent long-term FAA bill for almost three years, leading the 114 th Congress to approve a series of extensions, including a one-year extension ( P.L. 114-190 ) that expired at the end of FY2017. That act included a number of provisions addressing key aviation safety and security concerns. The 115 th Congress passed a six-month extension ( P.L. 115-63 ) of aviation funding and programs through the end of March 2018. Subsequently, the Consolidated Appropriations Act, 2018 ( P.L. 115-141 ), further extended authorization for aviation programs and airport and airway trust fund revenue authority through the end of FY2018. Proposals to reform ATC have been central to the legislative debate. FAA reauthorization measures considered in the House during the 114 th Congress ( H.R. 4441 ) and the 115 th Congress ( H.R. 2997 ) both included detailed provisions to establish a not-for-profit private corporation to provide the air traffic services currently delivered by FAA. In contrast, the Senate bills ( S. 2658 , 114 th Congress, and S. 1405 ) have not included any ATC reforms. On January 27, 2018, Representative Bill Shuster, chairman of the House Committee on Transportation and Infrastructure, announced that he would no longer insist on restructuring of ATC operations, and on April 13, 2018, he introduced H.R. 4 , which did not include ATC privatization language. An alternative plan to move ATC out of FAA but retain it under the Department of Transportation (DOT) was proposed as an amendment to H.R. 4 , but the amendment was not adopted. While privatization of ATC is no longer moving forward in either house, many in Congress continue to be interested in encouraging privatization of airports by expanding an existing pilot program. Changes to grant allocations for airport improvements remain in both H.R. 4 and S. 1405 , but proposals to raise long-standing caps on passenger facility charges collected by airports have not been included in either the House bill or the Senate committee bill. Other key issues in the debate have included concerns related to implementation of NextGen, FAA's plan for modernizing ATC, including options for encouraging aircraft owners to install needed avionics and addressing community noise impacts associated with flight path changes implemented to improve air traffic efficiency and capacity. Both bills include language to promote adoption of unmanned aircraft for commercial uses, such as inspection of critical infrastructure and package delivery, that involve flight beyond the aircraft operator's line of sight. The legislation also seeks to address aircraft parts certification processes, air carrier and repair station safety oversight, consolidation of ATC facilities, and FAA's oversight of the rapidly growing commercial space industry. In addition to FAA, the reauthorization bills would extend the Essential Air Service (EAS) program, which subsidizes commercial flights to small communities, and would address various airline consumer issues including the manner in which airfares are advertised and the size and spacing of aircraft seats. Most FAA programs are financed through the Airport and Airway Trust Fund (AATF), sometimes referred to as the Aviation Trust Fund. The AATF was established in 1970 under the Airport and Airway Development Act of 1970 (P.L. 91-258) to provide for expansion of the nation's airports and air traffic system. Between FY2014 and FY2018, the AATF has provided between 80% and 95% of FAA's total annual funding, with the remainder coming from general fund appropriations. Revenue sources for the trust fund include passenger ticket taxes, segment fees, air cargo fees, and fuel taxes paid by both commercial and general aviation aircraft (see Table 1 ). In addition to excise taxes deposited into the trust fund, FAA imposes air traffic service fees on flights that transit U.S.-controlled airspace but do not take off from or land in the United States. These overflight fees partially fund the EAS program. In 2017, the AATF had revenues of over $15 billion and maintained a cash balance of nearly $15 billion. The uncommitted balance was estimated to be approximately $5.9 billion at the end of FY2018, reversing several years of decline following the onset of the global economic crisis in 2008. The trust fund balance is projected to grow in the near term, as AATF revenue continues to rise and airport capital needs are projected to decline over the next five years. Changes in airline business practices may pose a risk to the AATF revenue structure. Trust fund revenue is largely dependent on airlines' ticket sales, and the spread of low-cost air carrier models has held down ticket prices and therefore AATF receipts. In addition, airlines increasingly impose fees for a variety of options and amenities, such as checked bags and onboard meals, rather than including them in the base ticket price. Generally, fees not included in the base ticket price are not subject to federal excise taxes. Air carriers generated over $4.57 billion in baggage fees alone in 2017, which would have brought more than $343 million into the trust fund had they been subject to the 7.5% ticket tax. This subject is not addressed in either H.R. 4 or S. 1405 . In recent years, FAA funding has totaled between $15 billion and $18 billion annually. Most recently, the Consolidated Appropriations Act, 2018 ( P.L. 115-141 ), provided funding through the end of FY2018. FAA funding is divided among four main accounts. The largest account, Operations and Maintenance (O&M), principally funds air traffic operations and aviation safety programs. The Airport Improvement Program (AIP) provides federal grants-in-aid for projects such as new runways and taxiways; runway lengthening, rehabilitation, and repair; and noise mitigation near airports. The Facilities and Equipment (F&E) account provides funding for the acquisition and maintenance of air traffic facilities and equipment, and for engineering, development, testing, and evaluation of technologies related to the federal air traffic system. The Research, Engineering, and Development account finances research on improving aviation safety and operational efficiency and on reducing environmental impacts of aviation operati ons. Proposed a uthorizations and appropriations for these accounts are shown in Table 2 . The federal government supports the development of airport infrastructure in three different ways: (1) AIP grants to airports, mainly for capital projects related to aircraft operations; (2) authorization for individual airports to assess a local passenger facility charge (PFC) on each boarding passenger; and (3) preferential income tax treatment on interest income from bonds issued by state and local governments for airport improvements (subject to compliance with federal rules). Airports may also draw on state and local funds and on operating revenues such as lease payments and landing fees. Different airports use different combinations of AIP funding, PFCs, tax-exempt bonds, state and local grants, and airport revenues to finance particular projects. Small airports are more likely to be dependent on AIP grants than large or medium-sized airports. Larger airports are much more likely to issue tax-exempt bonds or finance capital projects with the proceeds of PFCs. Each of these funding sources places various legislative, regulatory, or contractual constraints on airports that use it. The availability and conditions of one source of funding may also influence the availability and terms of other funding sources. The AIP provides federal grants to airports for airport development and planning. Participants range from very large publicly owned commercial airports to small general aviation airports that may be privately owned but are available for public use. AIP funding is usually limited to construction of improvements related to airside operations, such as runways and taxiways. Commercial revenue-producing facilities are generally not eligible for AIP funding, nor are operating costs. The structure of AIP funds distribution reflects congressional priorities and the objectives of assuring airport safety and security, increasing capacity, reducing congestion, helping fund noise and environmental mitigation, and financing small state and community airports. The main financial advantage of the AIP to airports is that as a grant program, it can provide funds for capital projects without the financial burden of debt financing, although airports are required to provide a relatively modest local match to the federal funds. Limitations on the use of AIP grants include the range of projects that the AIP can fund and the requirement that recipients adhere to all program regulations and grant assurances. Federal law requires the Secretary of Transportation to publish a national plan for the development of public-use airports in the United States. This appears as a biannual FAA publication called the National Plan of Integrated Airport System s (NPIAS) . For an airport to receive AIP funds, it must be listed in the NPIAS. The distribution system for AIP grants is complex.