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Factual Information


On 30 April 2005, at about 1033 Eastern Standard Time1, a Cessna Aircraft Company A152 (152) aircraft, registered VH-PVX, was being operated on circuit flying training at Hobart Airport, Tasmania. On board were a student pilot and an instructor. The pilot had been issued with a clearance by the aerodrome controller (controller) to conduct right circuits from runway 30 and to operate not above 1,000 ft above mean sea level.

At 1037, a Boeing Company 717-200 (717) aircraft registered VH-LAX, en route from Melbourne to Hobart, commenced the final leg of the Hobart runway 30 VOR2 instrument approach. The crew had been issued a clearance by the controller to conduct the final approach. The aircraft was being operated under the instrument flight rules. At about the same time, the controller instructed the pilot of the 152 to make a left orbit to enable the controller to visually separate the 152 with both the inbound 717 and another jet aircraft departing from runway 30. At that time the 152 was at the end of the downwind leg of the circuit.

At about 1039, the pilot of the 152 reported that the orbit was complete and the controller instructed the pilot to continue on the downwind leg and to report prior to turning on to the base leg. However, the pilot had not completed a full orbit but had 'rolled out' of the orbit after completing only a 270 degree turn, directly onto the base leg of the circuit. At that time the 717 was on the final approach leg of the circuit, 90 degrees to the left of the flight path of the 152 and converging.

At about 1041, when the pilots of both aircraft became aware of the potential conflict, the minimum horizontal distance between the two aircraft had reduced to between 400 and 500 m. The 717 was about 300 ft below the 152, and the pilots of both aircraft commenced avoiding action.

The Manual of Air Traffic Services (MATS) stated that visual separation shall be achieved by the use of visual procedures, or by assigning visual separation responsibility to a pilot. The MATS did not specify any minimum distance requirement for the application of visual separation. As the controller was unable to continue to visually observe separation between the 152 and the 717, and had not assigned separation responsibility to the pilot of the 152, there was an infringement of separation standards.

The routine aerodrome weather report (METAR) for Hobart issued at 1030, recorded the cloud as few3 at 3,000 ft and broken at 5,000 ft with visibility greater than 10 km. The pilot in command of the 717 and the controller later reported that the cloud was scattered at 4,000 ft while the 152 instructor believed the cloud base to be broken at about 3,000 ft.

The 152 instructor reported that he had a total of about 270 flying hours including 15 to 20 hours as an instructor. He was relatively new to Hobart and worked about 5 to 10 hours a week flying. He also worked casually in another non-aviation position with shifts that finished late at night or in the early morning.

The instructor believed that his inexperience, together with the cockpit workload involved in instructing the student pilot and controlling the aeroplane in moderately difficult crosswind conditions, reduced his situational awareness. He reported that he was not aware of the 717 on final, and believed he would not have had any opportunity to observe the aircraft until it was established on the final approach because of the low cloud in the area.

The controller had extensive experience in the provision of aerodrome control services at Hobart, and reported that the workload at the time of the occurrence was both moderately busy and complex.

The controller reported that he was applying visual separation between the 152 and several other aircraft. The MATS specified that:

When aircraft are operating visually as aerodrome traffic or in an Aerodrome Traffic Zone, ATC shall issue clearances designed to maintain separation; and/or sequencing instructions and/or relevant traffic information. Pilots shall be advised of their number in the landing sequence to assist in identification of traffic. The pilot will position the aircraft in such a manner that, while complying with ATC instructions, they maintain separation from other aircraft.

The requirement to provide traffic information was changed from 'mandatory (and)' to 'optional (and/or)' by Airservices Australia in April 2003. On 1 September 2005, Airservices Australia amended the MATS to completely remove the previously amended section relating to the provision of aerodrome traffic information, with the concurrence of the Civil Aviation Safety Authority (CASA), to remove ambiguity over separation responsibilities in the aerodrome traffic zone.

On 16 September 2005, the Civil Aviation Safety Regulation Part 172 Manual of Standards was amended, after agreement between CASA and Airservices Australia, to state:

When aircraft are operating visually as aerodrome traffic ATC must issue 1 or more of the following:

(a) clearances designed to maintain separation

(b) sequencing instructions

(c) relevant traffic information

The issue of the provision of traffic information is subject to an Australian Transport Safety Bureau (ATSB) safety recommendation4 (see also Safety Actions section of this report).

The Aeronautical Information Publication (AIP) GEN 2.14.3 also specified that:

ATC will provide relevant traffic information to aerodrome traffic to enable pilots, while complying with ATC instructions, to maintain separation from other aircraft.

The controller reported that the initial orbit instruction given to the pilot of the 152 was to allow for the departure of another jet aircraft and his plan was for the 152 to then extend on a downwind leg until it was possible for the 152 to safely follow the 717 on final. He had intended to pass the pilot of the 152 a number in the landing sequence when the pilot reported prior to turning base. However, as this report was not received, the pilot was not provided with either a number in the sequence or traffic information.

AIP GEN 4.4.1 specified that 'pilots must transmit a correct read-back of ATC clearances, instructions and information which are transmitted by voice' and ensure 'sufficient detail is included to indicate compliance'. The MATS 6.1.13 specified that ATC 'shall ensure that a correct read-back in sufficient detail is obtained'.

Both documents indicated that only key elements relating to certain clearance items must be read back, including 'level instructions, direction of turn, heading and speed instructions'.

The pilot of the 152 did not read back the instruction to continue on the downwind leg, nor did the controller request the read-back. There was no specific requirement in either the AIP or the MATS for the read-back to be provided.

The controller later acknowledged that a sequence number and traffic information should have been provided to the pilot of the 152 and that he believed that a read-back of the downwind instruction would have been beneficial.

Airservices Australia had an annual refresher training program for tower controllers that detailed several mandatory and optional training modules. One mandated module relating to separation assurance was not available to the Hobart controllers at the time of the occurrence.

The 717 flight crew was not provided with traffic information by the controller, but reported that they had been monitoring the radio transmissions between the controller and other pilots. Additionally they had observed the 152, initially on the traffic alert and collision avoidance system (TCAS),5 then visually, before commencing avoiding action.

  1. The 24-hour clock is used in this report to describe the local time of day, Eastern Standard Time (EST), as particular events occurred. Eastern Standard Time was Coordinated Universal Time (UTC) + 10 hours.
  2. Very high frequency omnidirectional radio range.
  3. Cloud amounts are reported in oktas. An okta is a unit of sky area equal to one-eighth of total sky visible to the celestial horizon. Few = 1 to 2 oktas, scattered = 3 to 4 oktas, broken = 5 to 7 oktas and overcast = 8 oktas.
  4. ATSB occurrence investigation report 200205540 and associated safety recommendation R20040063 available at www.atsb.gov.au.
  5. TCAS is an independent onboard collision avoidance system. It is designed as a backup to the ATC system and the 'see and avoid' concept.
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