Sutcliffe v. The Queen, 2006 DTC 2076, 2005 TCC 812 -- summary under Subparagraph 115(1)(a)(i)

The taxpayer was a U.S. resident who was employed by Air Canada as a pilot on domestic flights (between Toronto and other Canadian cities) and international flights (between Toronto and U.S. cities). His income from performing or exercising his employment in Canada was to be determined by reference to the estimated portion of his flights that occurred in the U.S. (including domestic flights that traversed U.S. airspace). Sickness and vacation pay, which should be viewed as part of his remuneration, should be apportioned on the same basis.