Sequence of events
At 0208 coordinated universal time (UTC) VH-FNB, a Fokker 50, departed Carnarvon for Perth southbound via air route B469 and was climbing to FL210. The two-way air route was a direct track between Carnarvon and Geraldton . VH-FNA, also a Fokker 50, had departed Geraldton for Learmonth and was tracking via the B469 northbound. The crew of FNA had reported to Perth Flight Service at 0201 that the aircraft was on descent to FL180 from FL200. At 0213, they reported at position HAMEL and were estimating overhead Carnarvon at 0246. HAMEL was a reporting point located 120 NM south-south-east of Carnarvon. FNB's estimated time of arrival at HAMEL was 0242.
About 65 NM south-south-east of Carnarvon and approaching FL180, the co-pilot of FNB glanced down at the traffic alert and collision avoidance system (TCAS) display and noticed a return in the 11-o'clock position at about 7 NM at the same level. The pilot in command of FNB, aware that FNA was likely to be in the area, communicated with the crew of FNA and requested their position. At 0226, as the pilot in command of FNA replied, the pilot in command of FNB saw FNA pass approximately 400 ft below his aircraft on a reciprocal track. FNA was not fitted with a TCAS and the crew of FNA did not see FNB. Flight service had not directed traffic information to either crew.
Flight Service procedures
Both aircraft were outside controlled airspace and operating in a directed traffic information environment in which air traffic control does not provide positive separation between air traffic. However, flight service was required to provide aircraft operating under instrument flight rules information on other possibly conflicting military or instrument flight rule traffic. The requirements and parameters for issuing traffic advice by flight service are in the Manual of Air Traffic Services. The procedures in the manual required the flight service officer to provide traffic information to the crews of both FNA and FNB about each other's flight routes because both aircraft were going to be within 15 NM of each other laterally and FNB was climbing through FNA's level.
When aircraft are planned to depart non-controlled airspace and enter controlled airspace, the flight service officer calculates a release time, which is the time at which the flight service officer expects the pilot of the aircraft to be communicating with air traffic control. When air traffic control receives notification from flight service that an aircraft will be entering controlled airspace, the controller calculates a time of acceptance when the aircraft is expected to be on frequency. Neither the release nor acceptance times are coordinated between flight service and air traffic control.
Flight Service Officer actions
The flight service officer was managing the combined sectors of Flight Service 1 and 8 at the time of the incident. Flight service team leaders were responsible for the administration of shifts. They did not provide active supervision of flight service officers at their work positions.
At the time of the incident, the flight service officer was responsible for monitoring 13 VHF and 8 HF frequencies, and 15 aircraft. Of the 15 aircraft, approximately 10 were active and the remainder were pending. Consequently, the flight service officer and his supervisor reported that the workload was considered light to moderate.
The flight service officer reported that he had assessed that after departure it would take FNB 15 minutes to climb through FL200 into controlled airspace. He therefore calculated that FNB would be in controlled airspace at about 0223 and he rounded up his expected release time to 0225. Air traffic control reported that they added a standard 15 minutes to the departure time advised unless the aircraft was known to have a low performance climb, such as the Fokker 50. In this case, 20 minutes was added. Therefore, the expected on-frequency time for FNB would have been 0228 and in accordance with standard practice, communications checks would have commenced by 0231.
The flight service officer reported that he would have normally passed traffic information to the pilots of both aircraft when FNB taxied at Carnarvon. The flight service officer was unable to explain why he did not believe the two aircraft were potentially conflicting. Following the incident, the flight service officer reported that he thought the Fokker 50 would have climbed at about 1,500 ft/min, a figure he reportedly derived from a previous conversation with one of the operator's pilots. Advice from the operator indicated that it was highly unlikely that a Fokker 50 could achieve such a rate-of-climb, particularly at the flight levels at which FNB was operating. The local flight service management reported that flight service did not advocate calculations based on rate of climb as a traffic assessment method.
The flight service officer reported that he filed the flight strip for FNB soon after the release time of 0225, believing the aircraft to be clear of non-controlled airspace.
The flight service officer had received some air traffic control training and reported that he had previously used air traffic control techniques to determine whether traffic was in potential conflict. The use of air traffic control techniques was not required or advocated in flight service procedures. The flight service officer had passed a performance check the day before, when the checking officer noted him using some air traffic control procedures to decide what traffic information should be provided. The supervisor counselled him at the time not to use such procedures. The flight service officer reported that he had been using air traffic control techniques for some time to determine what information needed to be passed to aircraft operating outside controlled airspace in an attempt to reduce the amount of, what he considered, unnecessary radio calls. Although the flight service officer had used unapproved procedures in the past, he did not have any history of providing inadequate or inappropriate traffic information. During the investigation, it was reported that other flight service officers who had undergone some air traffic control training were also known to have applied air traffic control procedures in the flight service environment.
The flight service officer reported that Airservices Australia had managed his career within the previous 2 years in such a manner that caused him concern because there was substantial uncertainty related to his future employment. The flight service officer also reported that as a result of this uncertainty, he was facing significant personal issues and was probably pre-occupied by these issues when he started the shift on the day of the incident. He had approached his local management prior to the incident for leave and the request was being processed at the time of the incident.
The flight service officer reported that he was uncertain about his future employment and as a result of this uncertainty he had only a small amount of sleep the night before his shift and was feeling tired at the time of the incident. The flight service officer's immediate supervisor reported that he was unaware that the flight service officer may have been experiencing significant personal stress or that the flight service officer was fatigued when he commenced duty.
Traffic alert and collision avoidance system
Both aircraft belonged to the same operator. The operator was introducing TCAS as each aircraft underwent a major servicing. FNB was the only aircraft in the operator's fleet that had been fitted with TCAS and not all of the operator's pilots had been trained in the use of TCAS. The operator's policy was that unless both pilots in a crew were qualified to use TCAS, then the equipment was only to be used in the traffic advisory (TA) mode. A TA is indicated on the equipment display to the crew when the aircraft are within about 48 seconds of their closest passing, based on projections derived from current flight path and speed.
FNB should have been reported as potential traffic to the crew of FNA since its track was planned to be within 15 NM laterally of FNA's route and because it was climbing through FNA's level.
The flight service officer reported that he would have normally passed traffic information to the pilots when FNB taxied at Carnarvon. However, on this occasion, he did not recognise that the two aircraft were potentially conflicting traffic. Having calculated a release time of 0225 when he expected FNB to be above FL200, in controlled airspace and therefore clear of FNA, he may have assumed that the traffic had no potential for conflict. An indication of his assumption was that he filed the flight strip for FNB soon after the release time; therefore, the potential for conflict of these two aircraft was never recognised by the flight service officer.
The flight service officer did not have a history of inadequately passing appropriate traffic information although he had, on occasion, used inappropriate air traffic control procedures.
The incident probably occurred as a result of a combination of factors. Firstly, the flight service officer reported that he was pre-occupied with his personal situation and was tired. As a result, he probably did not adequately monitor the progress of his routine actions. Secondly, he reported that he might have used a presumed rate of climb for the Fokker 50 as a basis for determining whether the traffic was potentially conflicting. Such a calculation was erroneous and irrelevant because the traffic assessment criteria in the Manual of Air Traffic Services required the traffic information to be passed. The use of this calculation may have been a manifestation of the flight service officer's occasional use of inappropriate procedures. His pre-occupation, tiredness and deviation from standard operating procedures may have contributed to the flight service officer losing situational awareness and as a result, he did not recognise that the flight paths of FNB and FNA were potentially conflicting.
Once the flight service officer had committed to not advising the crews of FNB and FNA of each other's presence, there were no organisational defences available, such as active supervision, to preclude the mistake going unnoticed. As a result, once the flight service officer had made the error, there was no backup.
Because the pilot in command of FNB did not need to take any avoiding action, it is unlikely that the provision of TCAS stopped an accident from occurring. However, the fact that TCAS had alerted the crew of FNB to the close proximity of traffic unknown to them indicated that it would have been the only defence available had the two aircraft been on a collision course. The effectiveness of TCAS in alerting and directing the crew of FNB to proximal traffic also illustrated the weakness of the principle of see-and-avoid.
The flight service officer was fatigued and distracted, probably as a result of stress and inadequate rest before commencing his shift. Consequently, he did not adequately monitor the progress of his routine actions and he did not notice that the two aircraft were potentially conflicting traffic. He did not provide traffic information to the pilots of the two aircraft as required by Manual of Air Traffic Services.
The key factors involved with this incident are common to other incidents investigated by the Bureau and which were the subject of safety recommendation R19990220 issued by the Australian Transport Safety Bureau (formerly BASI) to Airservices Australia on 19 January 2000.
Local safety action by Airservices Australia
Airservices Australia advised the ATSB that the existing flight service operations will continue until early 2001 when the national program of incorporating directed traffic information into TAAATS will be completed. Airservices is aware of the need to be vigilant in the management of this change process.
|Date:||06 August 1999||Investigation status:||Completed|
|Time:||1030 hours WST|
|Location:||130 km S Carnarvon, (VOR)|
|State:||Western Australia||Occurrence type:||Separation issue|
|Release date:||24 March 2000||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
Aircraft 1 details
|Aircraft manufacturer||Fokker B.V.|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Carnarvon, WA|
Aircraft 2 details
|Aircraft manufacturer||Fokker B.V.|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Geraldton, WA|