Just 60% of Air New Zealand's trans-Tasman flights took off within 15 minutes of their scheduled time last month.
A report by the Ministry of Transport shows airline performance for April.
78% of Jetstar's flights between Australia and New Zealand left on time, and 70% for Qantas.
Aviation commentator Peter Clark told Ryan Bridge Air New Zealand's has a large fleet, which means more planes needing attention.
He says aircrafts have to be turned around, serviced, and catered every flight.
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