gross income derived from Malaysia for the relevant period "gross income derived from Malaysia for the relevant period" means the total of all sums first receivable by the operator in the relevant period in respect of transporting by sea or air (whether before, in or after the relevant period) passengers or cargo embarked or loaded in Malaysia into ships or aircraft owned or chartered by the operator, except sums so receivable in respect of passengers or cargo - (a) brought to Malaysia, whether by the operator or otherwise, solely for transfer - (i) from one ship or aircraft to another; (ii) from a ship to an aircraft; or (iii) from an aircraft to a ship; or (b) so embarked or loaded into such a ship or aircraft if the call of that ship or aircraft at a port, aerodrome or airport in Malaysia for that embarkation or loading was a casual call within the meaning of subsection (6), less any sums received in the relevant period or prior thereto which are refunded in the relevant period and any sums first receivable in the relevant period or prior thereto which in the relevant period cease, otherwise than on the receipt thereof, to be receivable; ACT 53 - INCOME TAX ACT 1967 54. Sea and air transport undertakings.