An aviation expert believes the refining company behind last year's ruptured oil pipeline, is more at fault than fuel companies.

It comes after Air New Zealand's decision to take Z Energy and BP to court over the rupture, saying the disruption to jetfuel supplies cost the airline millions of dollars.

Both fuel companies say they'll be defending claims.

Aviation expert Irene King told Larry Williams while it unusual for an airline to sue one of their main suppliers she isn't surprised.

"I think that they think pretty clearly that they were incurring significant losses and they will take whatever action is necessary."

She says she believes the rupture was the refining company's problem.

"I suspect that this may be a way at actually getting to the refining company because I don't actually see that the fuel suppliers were at fault here."

LISTEN ABOVE AS IRENE KING SPEAKS TO LARRY WILLIAMS