thereof. . (3) Conforming amendments (A) Section 4081(d)(2) of such Code is amended by striking (a)(2)(C)(ii) and inserting (a)(2)(C)(ii)(I) . (B) Section 6427(l)(4)(B)(ii)(II) of such Code is amended by striking section 4081(a)(2)(C)(ii) and inserting section 4081(a)(2)(C)(ii)(I) . (C) Section 9503(c)(5)(B) of such Code is amended by striking 21.8 cents and inserting 35.9 cents . (b) Refund or credit in cases of reasonable cause Section 6427 of the Internal Revenue Code of 1986 is amended by inserting after subsection (e) the following new subsection: (f) Exception from increase in rate of tax for certain liquids used as fuel in non-Commercial aviation (1) Retail excise tax Except as provided in subsection (k), in the case of any fuel on the sale of which tax was imposed under section 4041(c) for which the rate of tax was determined under paragraph (3)(B) of such section, if the Secretary determines (pursuant to such regulations as are prescribed by the Secretary) that there is reasonable cause that the increase in the rate of tax pursuant to clause (ii) of such paragraph should not apply with respect to such fuel (such as in cases where the fuel was used in an aircraft which was engaged in scientific research, an evacuation from a natural disaster, or assistance in a medical emergency), the Secretary shall pay (without interest) to the ultimate purchaser of such fuel an amount equal to the increase in the amount of the tax imposed on such fuel pursuant to such clause. (2) Manufacturers excise tax Except as provided in subsection (k), in the case of any kerosene on which tax was imposed under section 4081 for which the rate of tax was determined under subsection (a)(2)(C)(ii) of such section, if the Secretary determines (pursuant to such regulations as are prescribed by the Secretary) that there is reasonable cause that the increase in the rate of tax pursuant to subclause (II) of such subsection should not apply with respect to such kerosene (such as in cases where the kerosene was used in an aircraft which