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The pilot of a Piper Aircraft Corporation Aerostar (Aerostar) had been issued with a clearance by the Tamworth aerodrome controller (ADC) to 'track east of the New England Highway until intercepting final runway 30R' at Tamworth and, subsequently, to 'report established east of the highway'. The voice recording of the occurrence confirmed that the clearance issued by the ADC to the pilot of the Aerostar clearly stated the route to be flown by that pilot. The pilot correctly read back the clearance and reported established east of the highway but did not remain east of the highway. The readback of the clearance, and confirmation from the pilot that the Aerostar was east of the New England Highway, enabled the ADC to clear the pilot of the Aerostar to descend below 4,000ft.

Tamworth Air Traffic Control (ATC) provided a non-radar, or procedural control, service to aircraft operating within the Tamworth control area and control zone. Controllers used non-radar information to establish and maintain procedural separation standards. The ADC intended to establish a lateral separation standard (between the Aerostar and a Pacific Aerospace CT4B (CT4) that was departing the Tamworth southern circuit). The standard used a '1 NM buffer to the track or position of an aircraft determined relative to a prominent topographical feature' in accordance with the Manual of Air Traffic Services. In this case the prominent topographical feature was the New England Highway that runs approximately south from Tamworth township and which crossed underneath the inbound track of the Aerostar approximately 12 NM southeast of the airport.

The vertical separation standard applicable between the CT4 and the Aerostar was 500 ft. However, the ADC applied a vertical distance of 1,000 ft between the Aerostar and the CT4 until the pilot of the Aerostar reported established east of the New England Highway. The ADC was then able to clear the pilot of the Aerostar for further descent because the ADC believed, based on the information provided by the pilot of the Aerostar, that a procedural lateral separation standard had been established between the Aerostar and the CT4, and between the Aerostar and other traffic operating in the southern circuit. However, the lateral separation standard was infringed when the Aerostar crossed to the west of the New England Highway, and the vertical separation standard was infringed when the Aerostar left 4,000 ft on descent, because no other separation standard had been established.

The pilot of the Aerostar was operating under the instrument flight rules (IFR) and later reported that he would have preferred to track with reference to his instruments, via IFR tracking points. The applicable Civil Aviation Regulation stated that the pilot shall 'ensure that maps and charts applicable to the route to be flown are carried and are readily accessible to the crew'. The pilot of the Aerostar carried a current world aeronautical chart that covered the Tamworth area but reported that he did not have time to refer to that chart after the clearance to track via the New England Highway had been issued. He was not carrying a visual terminal chart for Tamworth. He also reported that his workload at the time of the occurrence was high due to the combined effects of the sun in his eyes, the visual tracking instructions issued by the ADC and because he was unfamiliar with the airport.

The pilot of the Aerostar had a responsibility to advise the ADC that he was either uncertain about the clearance he had been issued, or that he was unable to proceed in accordance with the clearance issued. The ADC could then have issued an alternative clearance. Such timely notification is particularly important in a procedural environment where controllers rely on the integrity of the information provided by pilots to ensure the safe, orderly and expeditious flow of air traffic.

General details
Date: 24 June 2002 Investigation status: Completed 
Time: 1511 hours EST  
Location   (show map):13 km SE Tamworth, (VOR) Investigation type: Occurrence Investigation 
State: New South Wales Occurrence type: Loss of separation 
Release date: 20 February 2003 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: Piper Aircraft Corp 
Aircraft model: PA-60 
Aircraft registration: VH-IGN 
Serial number: 61-0682-7962142 
Type of operation: Aerial Work 
Damage to aircraft: Nil 
Departure point:Sydney, NSW
Destination:Tamworth, NSW
Aircraft 2 details
Aircraft manufacturer: Pacific Aerospace Corporation 
Aircraft model: CT/4 
Aircraft registration: VH-YCS 
Type of operation: Flying Training 
Damage to aircraft: Nil 
Departure point:Tamworth, NSW
Destination:Tamworth, NSW
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Last update 13 May 2014