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The Civil Aviation Authority is investigating an incident over Lake Wakatipu during which two passenger planes came close enough to spark an automatic warning to the two pilots.
Authority spokeswoman Emma Peel said yesterday an Air New Zealand Boeing 737 was approaching Queenstown Airport's runway last Saturday when it was warned by its "terrain collision avoidance system" another aircraft was in the area.
The pilot did a "standard" turn, to ensure he could see the other plane, a Glenorchy Air light aircraft, then landed.
"There was no risk of collision. The pilots could see each other. They were both in controlled airspace," she said.
Queenstown's Air Traffic Control unit notified the authority about the warning.
"It's not an uncommon incident, especially in a place like Queenstown which has tighter terrain with mountains all around."
The authority would review reports from Air Traffic Control, Glenorchy Air and Air New Zealand about the incident and decide whether any further action was needed, she said.
Transport Accident Investigation Commission spokesman Ken Mathews said the commission had been notified about the "lowest level" warning incident and had decided not to investigate.