(a) The Department may make loans to public airport owners for the purchase of any real estate interests as may be needed for essential airport purposes, including future needs, subject to the following conditions: (1) loans may be made only to public airport owners that are operating an airport as of January 1, 1999; and (2) loans may not be made for airports that provide scheduled commercial air service in counties of greater than 5,000,000 population. The loans are payable from the Airport Land Loan Revolving Fund, subject to appropriation. All repayments of loans made pursuant to this Section, including interest thereon and penalties, shall be deposited in the Airport Land Loan Revolving Fund. The Treasurer shall deposit all investment earnings arising from balances in the Airport Land Loan Revolving Fund in that Fund.