The Transport Accident Investigation Commission is calling for changes at Queenstown Airport after two Boeing 737's came within about 300 metres of each other over the resort town.
Its report details an incident in June 2010 when a Pacific Blue jet was landing and came close to a Qantas plane, also preparing to land.
The TAIC report says there was 304 metres of vertical separation between the two passenger aircraft.
It says Queenstown's air traffic control procedures are risky, because of the increasing numbers of big jets flying through mountainous terrain.
Controllers cannot see parts of the airspace because of mountains and therefore are unable to establish if low cloud will obstruct a pilot's view.
TAIC wants the Civil Aviation Authority to investigate Queenstown's procedures.