106 STAT. 1526 PUBLIC LAW 102-388 —OCT. 6, 1992 purchase, or lease with option to purchase, of buildings and associated facilities, and (b) instructional materials and equipment. Such funds are hereby authorized to be appropriated and may remain available until expended. The Federal Aviation Administration shall establish guidelines for determining the direct costs allowable under grants to De made pursuant to this section. The maximimi Federal share of the allowable cost of any project assisted by such grants shall be 65 percent: Provided further. That such Federal share shall be considered as having taken efTect on October 1, 1991. RESEARCH, ENGINEERING, AND DEVELOPMENT (AIRPORT AND AIRWAY TRUST FUND) For necessary expenses, not otherwise provided for, for research, engineering, and development, in accordance with the provisions of the Federal Aviation Act of 1958, as amended (49 U.S.C. App. 1301 et seq.), including construction of experimental facilities and acquisition of necessary sites by lease or grant, $230,000,000, to be derived from the Airport and Airway Trust Fund and to remain available until expended: Provided, That there may be credited to this appropriation funds received from States, coiuities, municipalities, other public authorities, and private sources, for expenses incurred for research, engineering, and development. GRANTS-IN-AID FOR AIRPORTS (LIQUIDATION OF CONTRACT AUTHORIZATION) (AIRPORT AND AIRWAY TRUST FUND) For liquidation of obligations incurred for grants-in-aid for airport planning and development under section 14 of Public Law 91-258, as amended, and under other law authorizing such obligations, and obligations for noise compatibility planning and programs, $2,000,000,000, to be derived from the Airport and Airway Trust Fund and to remain available xmtil expended: Provided, That none of the funds in this Act shall be available for the planning or execution of programs the commitments for which are in excess of $1,800,000,000 in fiscal year 1993 for grants-in-aid for airport planning and development, and noise compatibility planning and programs, notwithstanding section 506(e)(4) of the Airport and Airway Improvement Act of 1982, as amended, of which not to exceed $198,173,199 shall be available for letters of intent issued prior to June 30, 1992. AVIATION INSURANCE REVOLVING FUND The Secretary of Transportation is hereby authorized to make such expenditures and investments, within the limits of funds available pursuant to section 1306 of the Federal Aviation Act of 1958, as amended (49 U.S.C. App. 1536), and in accordance with section 104 of the Government (Jorporation Control Act, as amended (31 U.S.C. 9104), as may be necessary in carrying out the program set forth in the budget for the current fiscal year for aviation insurance activities under title XIII of the Federal Aviation Act of 1958.