The bill would amend the Single Business Tax Act to exempt from the tax base of a foreign corporation (organized outside the United States) that portion of its tax base attributable to the international operation of aircraft, if the corporation's gross income were exempt under Section 883(a) of the Internal Revenue Code. (Section 883(a) exempts from Federal taxation gross income, derived by a corporation organized in a foreign country, from the international operation of aircraft, if the foreign country grants an equivalent exemption to U.S. corporations.)