United States source gross transportation income
(1) In general Except as provided in paragraphs (2) and (3), the term “United States source gross transportation income” means any gross income which is transportation income (as defined in section 863(c)(3) ) to the extent such income is treated as from sources in the United States under section 863(c)(2). To the extent provided in regulations, such term does not include any income of a kind to which an exemption under paragraph (1) or (2) of section 883(a) would not apply.
26 USC § 887(b)(1)
None identified, default scope is assumed to be the parent (subpart C) of this section.