Boeing 737-700, VH-VBV

Summary

On 24 December 2003, a Boeing 737-7BK (737) operating under the instrument flight rules (IFR) was en route from Sydney and descending for a landing at Launceston, Tasmania. A Socata TB10 (Tobago) operating under the visual flight rules (VFR) was en route from Hobart, Tasmania, to Sydney at about 7,500 ft. As the 737 was descending through about 8,300 ft, at around 1333:53 ESuT¹, the crew received a traffic advisory (TA) from their traffic alert and collision avoidance system (TCAS) about the Tobago. This was followed approximately 15 seconds later by receipt of a TCAS resolution advisory (RA) to climb. The crew responded to the RA and after arresting the aircraft's rate of descent, climbed the aircraft to approximately 9,200 ft. The pilot in command of the 737 reported that the TCAS indicated that the Tobago passed the 737 within about 200 ft vertically, slightly to the left, and certainly less than 1 NM horizontally.

Both aircraft were operating in Class E airspace that was introduced as part of the National Airspace System (NAS) phase 2b on 27 November 2003. As no prescribed separation standards are applicable in these circumstances, there was no infringement of separation standards. However, TCAS data and information obtained from the pilots of both aircraft indicate that the aircraft came into such close proximity that a threat to the safety of the aircraft may have existed. Therefore, the occurrence has been classified by the ATSB as an airprox² event, which is a type of serious incident.

¹ Eastern Summer Time.
² Under the Transport Safety Investigation Regulations 2003, an 'airprox is defined as an occurrence in which two or more aircraft come into such close proximity that a threat to the safety of the aircraft exists, or may exist, in airspace where the aircraft are not subject to an air traffic separation standard, or where separation is a pilot responsibility.

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