Two planes coming in to land at Queenstown Airport risked getting too close together because of a mixup between pilots and an air traffic controller, the Transport Accident Investigation Commission has found.
In its report, released today, the Commission (TAIC) found it was clear that there was potential for abreach of the minimum required 1000 foot vertical separation between two Boeing 737-800s, operated by Qantas and Pacific Blue, on June 20, 2010.
The mountainous terrain surrounding the airport prevents pilots descending straight ahead to land, instead they must circle while descending until their aircraft is in position.
As the Pacific Blue pilots circled down, cloud obstructed their view of the runway, a situation requiring them to conduct a ``missed approach procedure''.
The plane then stopped circling and climbed directly to intercept the prescribed missed approach track.
However, the air traffic controller had been expecting to the plane to take a different path and continue circling.
Upon realising this, the controller instructed the Qantas plane to conduct a missed approach procedure of its own, and to climb at the maximum rate in order to maintain the required distance from the other plane.
TAIC did not investigate whether the minimum required distance between the two planes was actually breached, ``because it was clear that the potential for such a breach was high and that alone was a safety issue that needed addressing''.
TAIC found that the Pacific Blue pilots and the air traffic controller had different understandings of what would occur in the event the plane did not land after circling.
It also found that the various publications used by pilots and controllers that described landing and circling procedures were not consistent, which was a hazard likely to lead to misunderstanding.
"The circling manoeuvring that is required after a non-precision approach at Queenstown is a demanding procedure that ought to be reviewed for suitability,'' it said.
"A wider review of the Queenstown air traffic management system and operational procedures would be prudent, given the special features associated with operations at the aerodrome and the increasing number of commercial jet aeroplane operations.''
TAIC made a number of recommendations including that a system be installed to provide controllers with real-time observations of the weather conditions
