The crew of the Beech 1900D (B1900) aircraft had been cleared by the aerodrome controller (ADC) 1 to descend to 4,000 ft and were instructed to join the circuit via a left base leg for runway 12L (northern) circuit at Tamworth. The ADC 1 also instructed the crew to report approaching 4,000 ft. The crew acknowledged the clearance but later advised that they were unable to report approaching 4,000 ft due to frequency congestion. The ADC 1 had assigned 4,000 ft so that a procedural separation standard of 1,000 ft could be maintained with other aircraft until he could see the B1900 and apply visual separation.
The crew of the B1900 subsequently requested confirmation of their assigned level and reported their position when at 2NM north of the aerodrome. The controller then sighted the aircraft and cleared the crew to make a visual approach. The controller also asked the crew if they would need to extend through the centreline of runway 12L. The crew acknowledged the visual approach but did not advise the controller that they would need to extend through the centreline. The visual approach clearance authorised the crew to descend below 4,000 ft.
The crew of the B1900 could not comply with the instruction to join the circuit via a left base for runway 12L because the aircraft was too high and too fast. The co-pilot was the non-flying pilot and was undergoing command upgrade training. He had acknowledged the clearance for the visual approach and had previously acknowledged the instruction to join the northern circuit via a left base leg for runway 12L. At the time that the visual approach clearance was issued, the pilot-in-command was aware that they could not comply with the circuit entry instruction. He believed that the controller would have been aware that they were unable to enter the circuit on a left base leg, given their proximity to the circuit at that time and the height and speed of the aircraft. He also believed that the controller would have taken those circumstances, and the disposition of traffic in the southern circuit, into account when issuing the visual approach instruction.
The B1900 continued to descend and entered the runway 12R (southern) circuit airspace which was under the control of the ADC 2. The ADC 1 notified the ADC 2 that the B1900 had entered the southern circuit. The ADC 2 advised the ADC 1 that there was a Pacific Aerospace Corporation Airtrainer CT4B (CT4) on a right base leg for runway 12R. The ADC 2 provided traffic information about the B1900 to the crew of the CT4. There were four other CT4 aircraft inbound to the circuit at that time but the ADC 2 had not sighted them. The ADC 1 was unable to apply the required separation standard, either 1,000 ft vertically, or a minimum horizontal distance determined using the appropriate `Lateral Separation' standard from the Manual of Air Traffic Services (MATS), between the B1900 and the traffic inbound to the southern circuit. There was an infringement of separation standards.
The ADC 1 reported that he had sighted the CT4 on right base. He then instructed the crew of the B1900 to make a right turn and track via a right base leg for runway 12L. He believed that the B1900 was visually separated from that CT4 and that he could maintain visual separation between the B1900 and that CT4 with that instruction. He did not think that there had been an infringement of separation standards between the B1900 and the aircraft inbound to the southern circuit because all parties had enough time to ensure that visual separation was not infringed.
Although the crew was operating a regular public transport operation, the cockpit of the B1900 was a training environment and the Tamworth airspace was busy at the time of the occurrence. This led to a complex and dynamic situation in which the crew of the B1900 chose to continue descent, even though they were unable to comply with the circuit entry instruction. Had the B1900 remained at 4,000 ft until the crew could advise the ADC 1 that they could not track as instructed, the aircraft would have remained vertically separated with the traffic entering, and operating in, the southern circuit. That would also have provided the controller with time to evaluate the situation and issue alternative instructions.
The crew reported that they were unable to advise the ADC 1 that they could not comply with the circuit entry instruction due to frequency congestion. However, they had an opportunity to inform the controller when they acknowledged the clearance for the visual approach.
The controller believed that there had not been an infringement of separation standards between the B1900 and traffic inbound to the southern circuit. However, no standard had been established once the B1900 had left 4,000 ft on descent. The controllers did not have enough time to sight the inbound CT4s and apply visual separation because they expected the crew of the B1900 to comply with the clearance as acknowledged. Consequently, visual separation could not be applied because the ADC 2 had not sighted the inbound aircraft and no other procedural separation standard, in accordance with MATS, had been established between the B1900 and the inbound aircraft.
Local safety action
As at 24 June 2002, Airservices Australia had installed a tower situational awareness display (TSAD) in the equipment room in the Tamworth control tower complex so that appropriate maps can be loaded and system performance monitored. Airservices Australia expects to install the TSAD in the Tamworth control tower cabin in September 2002. Although the TSAD is not used to apply separation standards between aircraft, it should (when operational) assist controllers with situational awareness in this complex air traffic environment.
In an effort to control training in Tamworth controlled airspace, the Tamworth ERSA entry, effective 13 June 2002, now requires pilots planning instrument training at Tamworth, during tower hours, to obtain approval from Tamworth ATC prior to submission of the flight plan.
|Date:||27 June 2001||Investigation status:||Completed|
|Time:||1208 hours EST||Investigation phase:|
|Location:||4 km N Tamworth, Aero.||Investigation type:||Occurrence Investigation|
|State:||New South Wales||Occurrence type:||Loss of separation|
|Release date:||16 September 2002||Occurrence class:||Airspace|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
Aircraft 1 details
|Aircraft manufacturer||Beech Aircraft Corp|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Glen Innes, NSW|
|Departure time||1145 hours EST|
Aircraft 2 details
|Aircraft manufacturer||Pacific Aerospace|
|Damage to aircraft||Nil|
|Departure point||Tamworth, NSW|