SKYWEST AVIATION PTY LTD V THE COMMONWEALTH OF AUSTRALIA  ACTSC 20
Supreme Court of Australia Capital Territory – 14 March 1991
Skywest and the Commonwealth had a contract for air surveillance services. The contract referred to a clause which entitled Skywest to an increased payment based on the ‘purchase price’ of the aircraft. The provision referred to modified or unmodified aircraft. The remainder of the contract was silent on the issue.
The court had to decide on the admissibility of the surrounding circumstances to resolve the ambiguity.
The court had to address the issue of estoppel in the context of conduct leading to and following a formal written contract which expressly constitutes the whole of the agreement between the parties.