Near collision involving a Piper PA-28-140, VH-TOF and Piper PA-28-161, VH-PZN, 3 km south-west of Glenburn, Victoria, on 4 September 1995

VH-PZN was cleared from Mansfield to Melbourne at 4,500 ft. 30 miles northeast of Melbourne, VH-PZN advised approach radar of sighting an unexpected light aircraft, head-on at the same altitude. To avoid a collision, VH-PZN descended immediately and passed approximately 300 ft below and about 100 metres abeam the other aircraft.

The unidentified aircraft did not show up on radar as a secondary surveillance radar (SSR) return. After the breakdown in separation, its primary return was plotted by the radar controller. All attempts by Air Traffic Services (ATS) to contact the aircraft by radio were unsuccessful until the aircraft subsequently called Melbourne radar advisory service (RAS) landing at Wallan. In the meantime, a Piper PA34 assisted ATS by following the aircraft and identifying it as VH-TOF.

The pilot of VH-TOF subsequently advised that he did not see or hear VH-PZN at any time. He advised that he had been viewing property on the ground from above. He did not believe that he had climbed above 4,000 ft at any stage of his flight.

Both aircraft were flying in accordance with visual flight rules (VFR) in visual meteorological conditions (VMC) with a cloud base of 5,000 ft above mean sea level (AMSL).

Significant Factors

The following factors were considered relevant to the development of the incident:

1. The pilot of VH-TOF probably inadvertently climbed above 4,000 ft.

2. No SSR transponder returns were received from VH-TOF.

3. VH-TOF was not monitoring Melbourne radar advisory service frequency 135.7 MHZ within 35 miles radius of Melbourne until arrival at Wallan.