AO-1996-021

At 1105 hours on Tuesday 17 December 1996, Air New Zealand flight NZ 31 from Auckland to Brisbane, requested a clearance to climb from flight level 350 to non-standard flight level 370, because of turbulence at flight level 350. The level change was authorised by air traffic control, and as the aircraft left flight level 350, the crew noticed the "contrails" of another aircraft above and levelled off. A traffic alert and collision avoidance system traffic advisory message was received at the same time, indicating that the vertical separation of the aircraft on passing was 1800 feet. The loss of separation had the potential for a collision.

The safety issues discussed are the procedure for the use of flight progress boards and the issuing of clearances for non-standard flight levels. Safety recommendations were made to the Chief Executive of the Airways Corporation of New Zealand and the Director of Civil Aviation on these issues.