The Civil Aviation Authority is warning helicopter pilots to check their doors before take off.
The authority is getting an increasing number of reports of doors opening during flights among a number of helicopter makes and models.
In the most recent incident damage was caused when a rear door opened on an AS-350 helicopter while it was in the air.
The latest Helicopter Safety Update says the rear door became unlocked and slid partially open while the aircraft was descending after dropping skiers and their guide off .
The report says it appears the guide did not properly latch the door.
Two other incidents occurred in Nelson in January, and in Tasman district in May.