At 1543 Eastern Summer Time, the crew of a De Havilland DHC-8, operating under instrument flight rules (IFR), reported to the Flight Service 3 (FS3) officer that the aircraft had departed Armidale at 1543 for Sydney and was on climb to flight level (FL) 190. Two officers were operating the FS3 position: one officer was operating the radios and managing the flight progress strip display while the other was assisting at the coordination position. The crew of the DHC-8 had not been given a clearance to enter controlled airspace and consequently levelled the aircraft at FL125, which was the lower limit of the control area. The crew of the DHC-8 did not report this change of level to FS3, contrary to Aeronautical Information Publication (AIP) procedures (AIP NCTL - 4 paragraph 49.2).
While climbing to FL125, the crew of the DHC-8 was preoccupied with ascertaining the position of other traffic in non-controlled airspace on the FS3 frequency. There were between 18 and 21 aircraft on a number of retransmitted frequencies that were being monitored by FS3. Such a volume of traffic caused frequency congestion and made communication difficult. During this period, the FS3 operator was very busy providing traffic information to the pilots of IFR aircraft.
A Royal Australian Air Force Lockheed C130 aircraft, also operating under IFR, had departed Richmond for Walcha and was cruising in controlled airspace at FL130 on the reciprocal track to the DHC-8. The crew of the C130 had been cleared to leave controlled airspace on descent and was aware that the DHC-8 was opposite direction traffic below them. At 1548 the C130 crew reported leaving FL130 to the radar controller and changed to the FS3 frequency. However, to ensure that they could maintain separation with the DHC-8, they decided to maintain the aircraft at FL130 until they could establish contact with the crew of the DHC-8 on the FS3 frequency. Contrary to AIP procedures, the C130 crew did not report their intention to maintain the aircraft at FL130 to the radar controller nor did they report the aircraft's latest position of Mount Sandon to the FS3 operator. The FS3 coordinator stated that the frequency was "extremely congested" at the time.
At 1550 the crew of the DHC-8 changed to the Brisbane Centre radar control frequency in accordance with previous instructions from the FS3 officer. The crew reported their departure from Armidale and that the aircraft was approaching FL125. An airways clearance was not initially issued to the crew of the DHC-8. The Manual of Air Traffic Services (MATS 9-5-1 paragraph l) required controllers to positively identify aircraft prior to providing a radar service and to advise pilots whenever radar identification was established or lost. The radar controller did not notify the DHC-8 crew whether the aircraft was identified or not, but advised the crew of the DHC-8 that the C130 was 12 NM ahead and appeared to be maintaining FL130.
When the crew of the DHC-8 realised that a clearance was not imminent and that they were at a VFR level, they elected to descend to an IFR level, FL120. At that stage, the C130 was in controlled airspace with the crew attempting to communicate on the FS3 frequency (intended for the use by crews operating in non-controlled airspace) and the DHC-8 was in non-controlled airspace with the crew communicating with the radar controller (used by crews operating in controlled airspace).
At 1551.12, the radar controller advised the FS3 coordinator that the DHC-8 was still at FL125 and 8 NM directly ahead of the C130. The coordinator attempted to advise the FS3 officer of the situation but was unable to pass the information because of the number of transmissions from pilots. At 1551.16, the FS3 officer advised the crew of the C130 that they could disregard the DHC-8, as that aircraft was ".. well in controlled airspace". The comment implied that the DHC-8 was above the level of the C130. Based on his previous experience and understanding of the performance of DHC-8 aircraft, the FS3 officer believed that the aircraft had reached its cruising level and that it would not conflict with the C130. However, he had no ready means to confirm that the DHC-8 was in controlled airspace. This was not in accordance with the criteria for traffic assessment specified in MATS chapter 3, which stated that "..shall be passed traffic when an assessment of data indicates the possibility of a confliction, with the overriding spirit being, when in doubt advise".
At 1551.22 the crew of the C130 reported to FS3 that the aircraft had left FL130. The radar controller advised the crew of the DHC-8 that the C130 was directly ahead of them at 3 NM and suggested that they should return to the FS frequency. At 1551.43, the crew reported that they had descended to FL120 to establish 1,000 ft vertical separation with the C130 and returned to the FS3 frequency to attempt to contact the crew of the C130.
The radar controller was unsure of the intentions of the crew of the C130: consequently, he believed it was better to have the crew of the DHC-8 return to the FS3 frequency. Also, because of their proximity to each other, and because both aircraft were in or about to enter non-controlled airspace, with limited time available to relay advice, he believed that any attempt to give avoidance instructions at that stage could have resulted in a higher risk of collision. The final transmission from the radar controller to the crew of the DHC-8 was that the C130 was 1 NM ahead at FL120. The crew may not have heard this transmission as they were communicating with the crew of the C130 on the FS3 frequency.
At 1551.53, the crew of the DHC-8 was able to communicate with the crew of the C130 and they established that the C130 had just passed them. The crew of the DHC-8 reported that they saw the C130 pass to the left of their aircraft. The aircraft passed at FL120 within approximately 400 m of each other, in the cloud tops.
The investigation revealed that a combination of traffic disposition and the use of retransmission on the FS3 frequencies created a congested radio environment for the FS3 officer. As a consequence, the provision of reports by pilots and the provision of traffic information by the officer were constrained.
Following unsuccessful attempts to obtain a clearance to enter controlled airspace from the radar controller, the crew of the DHC-8 were also unable to report to FS3 that the aircraft was maintaining FL125 due to the congestion on the frequency. Similarly, the crew of the C130 was probably unable to report the Mount Sandon position to FS3 after changing to that frequency. Provision of a position report by the crew of the C130 or notification of the change in level by the crew of the DHC-8 would have assisted the FS3 officer to better appreciate the disposition of the aircraft.
The radar controller had advised the FS3 coordinator that the DHC-8 was in non-controlled airspace at FL125 and was traffic for the C130. However, this information was provided at a time when the FS3 operator was busy with transmissions from other pilots. Despite the coordinator's efforts, he was unable to advise the FS3 officer before the latter advised the crew of the C130 that the DHC-8 was not significant traffic. The FS3 operator should have verified the situation with the radar controller or alternatively advised the crew that the position of the DHC-8 was unknown.
The crew of the C130 were aware of the oncoming DHC-8 and had remained at FL130 for a further 3 minutes while attempting to report to FS and to contact the crew of the DHC-8 to arrange separation. Once the FS3 officer told them that they could disregard the DHC-8, the crew of the C130 descended the aircraft and unknowingly placed it in conflict.
While still at FL130 in controlled airspace, the crew of the C130 was having difficulties communicating with FS3 and the crew of the DHC-8. Had the crew of the C130 advised the radar controller of their intention to maintain FL130, it is likely that the controller would have been prompted to provide greater assistance to resolve the conflict.
- A significant number of pilots were operating on the flight service frequency, which made it difficult for crews to report their positions or exchange information for traffic avoidance.
- The crew of the DHC-8 did not report their intention to change flight level to the flight service officer.
- The crew of the C130 did not report the Mount Sandon position to the flight service officer.
- The crew of the C130 was unable to contact the crew of the DHC-8 to arrange separation between the aircraft, due to frequency congestion.
- The crew of the C130 did not report that the aircraft was maintaining FL130 to the radar controller after previously reporting leaving that level.
- The flight service officer did not provide directed traffic information in accordance with MATS.
- The flight service officer assumed that the DHC-8 had entered controlled airspace and subsequently provided unverified information to the crew of the C130.
- The crew of the C130 received incorrect traffic information on the DHC-8.
As a result of investigation into this and similar occurrences, the Bureau of Air Safety Investigation issued the following interim recommendations to Airservices Australia:
IR970112 (issued on 14 July 1997)
"The Bureau of Air Safety Investigation recommends that Airservices Australia review the provision of air traffic services to maximise the use of the currently available radar coverage particularly on routes used by regular public transport aircraft.
The following response was received from Airservices Australia on 21 October 1997:
"Airservices Australia is reviewing the provision of air traffic services with regard to maximising the use of radar services both within and outside controlled airspace".
As you are aware, the Airspace 2000 proposal which Airservices planned to introduce on the 26th February 1998, comprehensively addresses the extension of radar services. These radar enhanced services include:
Radar Class E airspace from Cairns to Melbourne above 8,500 feet.
A Radar - Information Service (RIS) in Class G airspace within radar coverage.
The Board of the Civil Aviation Safety Authority (CASA) has deferred making a decision on the proposal. Regardless of the outcome of the Airspace 2000 review by CASA, Airservices intends proceeding with three initiatives to enhance radar services on the 26th of February 1998.
Radar Class E airspace will be introduced between 8500 feet and FL125 outside existing Class C airspace from Grafton to Canberra within radar coverage. Brisbane Enroute will provide radar services within the Class C control area steps over Coffs Harbour down to 4500 feet. Sydney Terminal Control Unit will provide radar services to 45nm Sydney in non controlled airspace on a discrete frequency. These initiatives will increase Airservices use of existing radar coverage for air traffic services. Further expansion of radar services is limited pending decisions on Airspace 2000 by CASA."
Response classification - CLOSED-ACCEPTED
IR980005 (issued on 24 March 1998)
"The Bureau of Air Safety Investigation recommends that Airservices Australia review the guidance in the MATS for the passing of traffic information by ATS personnel to ensure pilots have adequate time to assess the potential for conflict with other aircraft".
The following response (in part) was received from Airservices Australia on 27 May 1998:
"ATS Operational Policy Branch is developing comprehensive procedures for processing traffic information under the new environment".
Response classification: OPEN
IR980021 (issued on 24 March 1998)
"The Bureau of Air Safety Investigation recommends that Airservices Australia review ATS proficiency and continuation training requirements with a view to personnel undertaking specific traffic information simulator training on a regular basis".
The following response was received from Airservices Australia on 27 May 1998:
"Airservices has developed its refresher training program for delivery to operational Air Traffic Services officers to emphasise elements dealing with the provision of traffic information and actions to be taken when separation has or may have been compromised".
Response classification: OPEN
IR980059 (issued on 22 April 1998)
"The Bureau of Air Safety Investigation recommends that Airservices Australia review air traffic service procedures relating to the combining of a number of operator positions and/or frequencies with a view to reducing the impact of frequency congestion.
The following response was received from Airservices Australia on 4 June 1998:
In addition to AIC H34/97, Airservices provides direction to ATS staff regarding the use of retransmit facilities in MATS 12-4-2 which shows "To reduce frequency congestion and interference on pilot broadcasts or other pilot-to-pilot communications being used for self separation, the retransmit facility should be operated in the "OFF" mode whenever practicable."
A number of other factors, in the context of the Airspace 2000 initiatives, relating to the provision of services are currently being discussed with CASA. Implementation of aspects of these initiatives would affect not only the way services are provided but the way in which ATS frequencies are used.
Airservices will continue to monitor the effects of retransmit facilities pending resolution of a number of issues associated with the implementation of CASA's Airspace 2000 initiatives".
Response classification: OPEN
Additionally, the Bureau of Air Safety Investigation is investigating a safety deficiency relating to Air Traffic Services' responses to in-flight emergencies.
Any safety output issued as a result of this deficiency analysis will be published in the Bureau's Quarterly Safety Deficiency Report.
|Date:||10 September 1997||Investigation status:||Completed|
|Time:||1650 hours EST|
|Location:||61 km S Armidale, Aero.|
|State:||New South Wales||Occurrence type:||Near collision|
|Release date:||23 April 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||Armidale, NSW|
|Departure time||1643 hours EST|
Aircraft 2 details
|Aircraft manufacturer||Lockheed Aircraft Corp|
|Type of operation||Military|
|Damage to aircraft||Nil|
|Departure point||Richmond, NSW|
|Departure time||1617 hours EST|