The aerodrome circuit was active with a number of aircraft conducting circuit training, or inbound for landing. Both runways 35 and 30 were in use. Runway 30 intersected runway 35 approximately 750 m from its threshold. The tower was staffed with three controllers operating the aerodrome control (ADC), coordination and surface movement control positions.
The ADC had instructed the crew of a De Havilland Dash 8 (Dash 8) to line up for a departure from runway 35. The pilot of an American Aircraft Corporation Cheetah (Cheetah) had been instructed to continue approach for runway 30. The ADC cleared the Dash 8 crew for takeoff and then looked towards the final approach path for runway 30 to monitor the approach of the Cheetah. As the ADC completed the transmission to the Dash 8 crew, he saw that the Cheetah was on short final and immediately transmitted an instruction to the Dash 8 crew to hold their position. This instruction was over-transmitted by the acknowledgment of the take-off clearance by the pilot in command of the Dash 8. The ADC commenced to issue a land-and-hold-short instruction to the pilot of the Cheetah; however, seeing that the Dash 8 was starting it's take-off roll, he ceased the transmission and issued a further instruction to the Dash 8 crew to hold position. This instruction was over-transmitted by the Cheetah pilot reporting that he was initiating a go-around. The Dash 8 became airborne prior to the intersection of the runways, however, the crew held their aircraft at approximately 50 ft above ground level while the Cheetah passed approximately 100 ft above and slightly behind the Dash 8.
The automatic voice recording of the radio transmissions from the ADC during this period indicated that there were few or no intervals between any of his transmissions. The pilot of another aircraft that was operating in the circuit heard the hold-short instruction. The crew of the Dash 8 reported that they did not hear either of the hold-short instructions.
The ADC had formulated a traffic plan but this changed when a turbojet aircraft he thought was going to conduct a full-stop landing on runway 35, conducted a touch-and-go. The ADC had instructed the crew of the Dash 8 to line up on runway 35 after the approach of the turbojet aircraft, and had amended the approach of the Cheetah to runway 30 to facilitate the departure of the Dash 8. The ADC did not instruct the pilot of the Cheetah to report at a position that would have enabled him to adjust the traffic sequence if required. There was also a delay between the time the ADC approved the Dash 8 crew to line up, and the eventual issue of the departure instructions and a clearance. This delay was due to radio transmissions from the pilot of the turbojet aircraft, as well as the coordination of inbound traffic with the approach controller. During this period, the Cheetah pilot had continued his approach to runway 30. The ADC did not check the position of the Cheetah in relation to the intersection of the runways prior to issuing the take-off clearance to the Dash 8 crew. That was done as he was completing the transmission of the take-off clearance to the crew. As a final action to resolve the conflict between the aircraft, the ADC proposed to issue a land-and-hold-short instruction to the pilot of the Cheetah; however, the landing distance available (590 m) to the pilot did not meet the distance required (900 m) for land-and-hold-short operations.
The Manual of Air Traffic Services details the radiotelephony phraseology (RTF) to be used by controllers to cancel take-off clearances or to stop a takeoff in emergency conditions. The ADC used only part of the required RTF for the cancellation of the take-off clearance. He did not use the RTF for an emergency situation.
The complexity of the traffic sequence for the ADC was increased by the amount of traffic in the area, and by the fact that the pilot of the turbojet aircraft conducted a go-around. However, had the ADC instructed the Cheetah pilot to report prior to turning base or final for runway 30, he would have had some options to better manage the traffic sequence. The ADC could have also utilised one of the other controllers to assist in the sequencing of the traffic, by monitoring the flight of the Cheetah.
Once the ADC recognised that the use of the intersecting runways was not possible, the use of the appropriate and complete RTF for the situation would have assisted in minimising the possibility for conflict. Under the circumstances, the use of the RTF for emergency conditions may have been appropriate. In his haste to ensure that the Dash 8 received the instruction to hold, the ADC compounded the situation by not allowing the crew time to acknowledge the take-off clearance prior to issuing the hold instruction. Had the ADC transmitted after the crew had completed their acknowledgment, it is probable that they would have clearly received, and been able to safely respond to, the hold instruction.
The use of land-and-hold-short procedures for the particular runways in use was not an option for the ADC.
|Date:||07 November 1998||Investigation status:||Completed|
|Time:||1610 hours ESuT|
|State:||Australian Capital Territory||Occurrence type:||Loss of separation|
|Release date:||23 July 1999||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
Aircraft 1 details
|Aircraft manufacturer||de Havilland Canada|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Canberra, ACT|
Aircraft 2 details
|Aircraft manufacturer||American Aircraft Corp|
|Type of operation||Private|
|Damage to aircraft||Nil|