Boeing 737-376, VH-TAX

The crew of a departing Boeing 737 (B737) reported that as they were climbing to 5,000 ft on a standard instrument departure from runway 27 at Melbourne, they saw an arriving B737 on descent in their 12 o'clock position, passing from right to left. The departing aircraft's traffic alert and collision-avoidance system indicated that there might have been less than the required radar separation standard of 3 NM between the two aircraft. The crew was not alerted by air traffic control regarding the arriving B737.

Radar data and air traffic control automatic voice recordings were reviewed to establish the sequence of events. The investigation found that the Departures controller had assigned responsibility for separation to the pilot of the arriving B737, which was tracking for left downwind runway 34. The transmission from air traffic control to the crew of the descending B737 included the statement "...clear of the 737 out to your left, descend to 3000".

Airservices Australia advised that the procedure was used when separating runway 27 departing aircraft from arriving aircraft tracking on left downwind for runway 34. The aim was to release the climb and descent restrictions of both aircraft as soon, and as efficiently, as possible. The procedure of one aircraft sighting and confirmed past the other aircraft was considered to be a legitimate technique in such situations.

Visual separation of air traffic may have been a valid method to use in those circumstances. However, the criteria for its application were clearly detailed in the Manual of Air Traffic Services (MATS) Part 4 Section 5. In particular, MATS 4.5.1.11 stated: "In circumstances where an aircraft has been instructed to maintain separation from, but not follow, an IFR aircraft, traffic information shall be issued to the IFR aircraft, including advice that responsibility for separation has been assigned to the other aircraft". The departing B737 was an IFR aircraft but was not provided with the required traffic information.