A failed oil pressure sensor on a backup generator could be the reason Air New Zealand’s computer system crashed on Sunday for six hours, IBM confirmed this morning.

The IT failure caused disruptions to more than 10,000 Air New Zealand customers, who were delayed by two hours on average. The computer failure affected the company's booking and check in systems. Passengers had to be manually checked in, which caused further delays.

Air New Zealand apologised to its customers yesterday saying the incident should never have happened.