Saab AB340, VH-OLM and De Havilland Canada Dash 8, VH-TQV

On 17 January 2005, at 0633 Eastern Daylight-saving Time, a Saab Aircraft Company AB SF-340B (Saab) departed Albury Airport on a scheduled passenger service to Sydney, NSW. The aircraft was being operated under the instrument flight rules (IFR). The crew had been authorised by the Albury Tower aerodrome controller to track via Yass on the 043 degree radial from the Albury very high frequency omni-directional radio range (VOR) navigation aid and to climb to flight level (FL) 170. At 0636, a de Havilland Canada DHC-8-102 (Dash 8) aircraft departed Albury Airport on a scheduled passenger service to Sydney, also under the IFR. The crew of the Dash 8 were issued with a clearance by the aerodrome controller to track via the 055 degree radial from the Albury VOR and to climb to FL200.

Aviation Safety Recommendations

| Air Safety Recommendation R20050010 | Air Safety Recommendation R20050011

FACTUAL INFORMATION

On 17 January 2005, at 0633 Eastern Daylight-saving Time, a Saab Aircraft Company AB SF-340B (Saab) departed Albury Airport on a scheduled passenger service to Sydney, NSW. The aircraft was being operated under the instrument flight rules (IFR). The crew had been authorised by the Albury Tower aerodrome controller to track via Yass on the 043 degree radial from the Albury very high frequency omni-directional radio range (VOR) navigation aid and to climb to flight level (FL) 170. At 0636, a de Havilland Canada DHC-8-102 (Dash 8) aircraft departed Albury Airport on a scheduled passenger service to Sydney, also under the IFR. The crew of the Dash 8 were issued with a clearance by the aerodrome controller to track via the 055 degree radial from the Albury VOR and to climb to FL200.

The Albury aerodrome controller was required to apply non-radar, or procedural, control, in accordance with published procedures, to aircraft operating within the Albury control zone (CTR) and control area (CTA) up to 8,000 ft. Procedural control is achieved by the use of information from sources other than radar. The aerodrome controller later reported that he established a difference of 12 degrees between the tracks of the two aircraft to facilitate the application of a visual separation standard. Visual separation at Albury was achieved by the use of information from sources other than radar. According to the Manual of Air Traffic Services (MATS) 4.5.2.2 (effective 10 Jun 2004):

Aerodrome controllers may also separate by the use of visual observation of aircraft position and projected flight paths.

The airspace above the Albury CTR and CTA was the responsibility of the Hume sector controller (Hume controller) operating in the Melbourne Air Traffic Control Centre. The Hume controller was required to provide a procedural air traffic control (ATC) service to aircraft operating within the Hume sector until that controller could establish a radar separation standard. The minimum horizontal radar separation standard applicable in the Hume sector was 5 NM.

To ensure that a procedural separation standard was maintained between the aircraft in the Hume sector, the Hume controller instructed the Albury aerodrome controller to establish the two aircraft in a step-climb procedure. MATS 4.3.1.8 stated that:

A step climb procedure may be used to simultaneously climb aircraft to vertically separated levels provided that the lower aircraft is progressively assigned levels which provide vertical separation with the higher aircraft.

The Albury aerodrome controller later reported that a step-climb was not practical, because there was insufficient vertical spacing between the two aircraft when he requested altitude reports from the crews. The Albury aerodrome controller did not notify the Hume controller that he was unable to implement the step-climb procedure or that he would provide visual separation until a radar standard was established.

MATS 4.1.1.4 stated that:

Tactical Separation Assurance places greater emphasis on traffic planning and conflict avoidance rather than conflict resolution. This is achieved through:

a. the proactive application of separation standards to avoid rather than resolve conflicts;

b. planning traffic to guarantee rather than achieve separation;

c. executing the plan so as to guarantee separation; and

d. monitoring the situation to ensure that plan and execution are effective.

ANALYSIS

The investigation concluded that there was no infringement of separation standards, because the Albury aerodrome controller reported that he maintained a visual separation standard, in accordance with the Manual of Air Traffic Services (MATS), between the Saab and the Dash 8, until the Hume controller advised that he had 'just over 7 miles' between the two aircraft.

The Albury aerodrome controller did not establish a step-climb procedure between the two aircraft in accordance with the terms of the clearance as coordinated with the Hume controller. The aerodrome controller should have advised the Hume sector controller that he was unable to comply with the terms of that clearance. Both controllers could then have coordinated another mutually acceptable clearance before the aerodrome controller transferred control of the aircraft to the Hume controller. The establishment of a step-climb procedure would have ensured that a procedural separation standard continued to exist between the aircraft until such time as the Hume controller established a radar separation standard and accepted responsibility for the aircraft.

The Albury aerodrome controller was required to establish a procedural separation standard between the two aircraft and to have that standard in place before transferring the responsibility for separation to the Hume controller.

The aerodrome controller's use of visual separation technically complied with the separation provisions stated in the MATS for Albury tower procedural separation purposes. However, use of that procedure did not meet the Hume controller's requirements for procedural separation and would not have ensured that separation continued to exist in the event that the aerodrome controller lost sight of one or both of the aircraft. Furthermore, it did not demonstrate 'the proactive application of separation standards to avoid rather than resolve conflicts' as stated in the MATS.

The ability of a sector controller to apply a separation standard using radar may be influenced by factors such as the sector controller's workload, or a failure of an aircraft's transponder, for example. Therefore, aerodrome controllers cannot anticipate when a sector controller may be able to establish a radar separation standard. In the event that the sector controller could not establish a radar standard, the application of an appropriate procedural separation standard that could be used by both controllers would have ensured that separation continued to exist. Such a procedure would have complied with the separation assurance provisions of the MATS.

Technical adherence to the provisions of one separation standard may not guarantee that separation will continue to exist. In this circumstance, the aerodrome controller relied on being able to continue to apply an interpretation of visual separation between the two aircraft until he anticipated that the sector controller could separate the aircraft using radar. While only one separation standard needs to be applied for separation to exist, contingencies such as controller workload and other traffic might preclude the application of another form of separation before the minima of that one standard are infringed. The application of the tactical separation assurance provisions specified in the MATS should assist controllers to anticipate such contingencies and, in doing so, help avoid, rather than resolve, conflicts.

SAFETY ACTION

Airservices Australia safety action

At a conference of regional tower managers held in February 2005, Airservices Australia's Airport Services undertook, among other initiatives, to develop a check and standardisation regime across regional tower units to help ensure that controllers' understanding of the application of separation standards does not vary between towers.
In its report on standardisation issues of 19 May 2005, produced as a result of that conference, Airport Services identified the potential for variations in the interpretation and application of visual separation. The report suggested that the wording in the Manual of Air Traffic Services 'be amended to reinforce the need for other approved separation to be assured before and after the application of visual separation'.