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Interim Recommendation issued to: AirServices Australia

Recommendation details
Output No: IR19980005
Date issued: 24 March 1998
Safety action status:
Background:

Safety Issue

The provision of timely traffic information to flight crew.

OCCURRENCE SUMMARY

Occurrence 9702191

A De Havilland Dash 8 (Dash 8) was on climb to FL210 and was tracking between Horn Island and Cairns. The crew was given traffic information on an Embraer Brasilia (Brasilia) which was en-route from Cairns to Bamaga. The crew of the Brasilia was cleared by air traffic control (ATC) to leave controlled airspace on descent and was then provided with traffic information on the Dash 8. Prior to leaving controlled airspace, the crew of the Brasilia was unable to establish communications on the area frequency with the crew of the Dash 8. The pilot of the Dash 8 recalled that he saw the shadow of the Brasilia as the aircraft passed each other.

Occurrence 9702426

A Shorts SH36 (Shorts) aircraft was maintaining 9,000 ft and was on a flight from Williamtown to Brisbane. As it approached Taree, the crew was given traffic information on a Dash 8 which was on a flight from Sydney to Taree via Williamtown at FL150. The crew of the Dash 8 was approved to leave controlled airspace on descent and was instructed to transfer to the flight service frequency. Due to frequency congestion, the crew was unable to seek traffic information from flight service in order to assess the potential for conflict with the Shorts. The relevant information was not obtained until the Dash 8 was descending through 11,000 ft. The crew discontinued the aircraft's descent at 10,000 ft and avoided further conflict with the Shorts.

Occurrence 9704231

Two Boeing 737s (B737s) were at the same level and approaching Parkes from the west on converging tracks. The sector controller believed that he would be able to establish a 30-NM longitudinal separation standard between the aircraft, before lateral separation reduced to less than required. However, other aircraft in the vicinity limited the controller's choice of levels for the B737s. In addition, one of the B737s was unable to meet an amended level requirement. As a result, the distance between the two aircraft reduced to 18 NM before the controller was able to identify and separate the two aircraft, by radar. The controller did not issue traffic information to the B737 crews, nor were emergency separation measures implemented.

SAFETY DEFICIENCY


Flight crews are not being provided with, or are unable to obtain, traffic information in sufficient time to adequately assess the potential for conflict with other aircraft.

ANALYSIS

The provision of traffic information by air traffic services (ATS), or the facilitation by ATS for the gathering of traffic information by flight crew, is integral to the continuing safe conduct of flights. In 1997, there were 26 occurrences in which aspects of the provision of traffic information was a factor. In seven of these occurrences the timing of the provision of traffic information by ATC was a factor. In two other occurrences the lack of provision of traffic information, after separation had reduced to less than the required minimum standard, was a factor.

ATS procedures

The timely establishment of communication with the flight crew of other aircraft is necessary for flight crew whose aircraft is about to leave controlled airspace or is operating in non-controlled airspace. This communication enables them to determine the position of other aircraft operating in their vicinity and then to avoid those aircraft.

Generally, when flight service (FS) identify a need for the provision of traffic information to the flight crew of an aircraft intending to leave controlled airspace, they provide the traffic information to ATC for relay to the crew. Alternatively, subject to traffic and other requirements, ATC transfer the crew to FS in order for that agency to provide the traffic information.

When ATC issue the traffic information, it is often passed either just before, or after the crew has been instructed to leave controlled airspace on descent. When FS issue the traffic information, the crew are often instructed by ATC to contact FS at "top of descent". Whilst the aircraft may still be within controlled airspace, it may be close to the boundary between controlled and non-controlled airspace. In both situations, the crew usually have a high workload and may develop a mindset that commits them to a course of action before being able to adequately assess the traffic information or establish communications with aircraft in non-controlled airspace.

Provision of traffic information by FS or ATC, or the establishment of communication by the flight crew with other aircraft just prior to entering non-controlled airspace, may have been appropriate for earlier generations of aircraft. However, this practice is incompatible with most modern regional airline and general aviation aircraft due to the higher performance capabilities of these aircraft. Many of these modern turbo-propeller or turbo-jet aircraft are capable of considerably higher airspeeds and rates of climb/descent than the older piston-powered aircraft. Consequently, following the provision of traffic information by FS or ATC, there is usually little time available for the crew to assess the conflict potential with other aircraft and then to communicate with the crews of those aircraft, prior to leaving the protection afforded by controlled airspace.

The problem resulting from the higher performance of modern aircraft is compounded by the inherent delay between when an aircraft commences descent and when the crew actually report "on descent" to ATS. This delay can be up to 1 minute after the aircraft has vacated a previously maintained level. During this period, a modern regional airline aircraft may have descended or climbed up to 1,500 ft and travelled up to 5 NM. Again, aircraft operating in close proximity to the boundary between controlled and non-controlled airspace may conflict with other aircraft operating in non-controlled airspace before the flight crew has received traffic information.

Emergency provision of traffic information

When a separation standard does not exist and in a controller's opinion, traffic proximity warrants, the controller is required to issue traffic information to the crew of the aircraft concerned (Manual of Air Traffic Services (MATS) 4-6-1 paragraph 6). Evidence from investigations indicates that some ATS personnel are reluctant to issue traffic information after separation has reduced to less than the required standard. Consequently, flight crews have been unable to assess the potential for conflict while aircraft have been in close proximity. The failure to utilise flight crew to assist in the resolution of a reduction in separation may compromise aircraft safety.

Training

The investigations revealed that in some situations, this reluctance by controllers to provide traffic information was due to unfamiliarity with the process. While the provision of traffic information is included in some ATC simulator exercises, the timeliness of the advice to pilots does not appear to be an aspect given much consideration. Additionally, the training scenarios available to assist controllers to improve their delivery of traffic information are limited. There is no specific requirement for controllers to regularly practise the routine provision of traffic information, or the provision of emergency traffic information. Implementation of specific traffic information scenarios and the regular use of these in a simulator would assist controllers to improve the assessment, timing, and awareness of those situations in which the provision of traffic information is required.

Flight progress strip annotation

The guidance provided to personnel regarding the recording of the provision of traffic information on flight progress strips (FPSs) is in the MATS 10-1-4 paragraph 30. A controller or flight service officer is required to both enter and tick the identification of conflicting traffic after the information has been passed and acknowledged. A better procedure may be to annotate the conflicting traffic on the FPSs as soon as the conflict is recognised. In this way the annotation can be a cue for further action. A tick should then be placed beside the conflicting traffic annotation only after it has been issued to, and acknowledged by, the relevant aircrew. This aspect could be clearly stated in the MATS and the procedure covered in specific traffic information training undertaken by ATS personnel.

The provision of prompts to assist controllers, as described, is an aspect that may require further consideration due to the pending use of electronic FPSs with the introduction of The Australian Advanced Air Traffic System (TAAATS).

Output text

Safety Interim Recommendation

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.

Initial response
Date issued: 17 November 1998
Response from: AirServices Australia
Action status: Monitor
Response text:

Airservices has revised the methodology and parameters for passing traffic information in its "proposal to amend G Airspace procedures- originally planned for introduction on 16 July 1998.

This procedure amendment has been deferred until later in 1998 to facilitate further consultation and development.

ATSB response:

The following letter was sent to Airservices Australia on 6 December 1999:

Subject: Outstanding airspace related safety actions

Responses to some previous safety recommendation to Airservices Australia and the Civil Aviation Safety Authority (CASA) proposed actions that were subject to the latter's Airspace 2000 initiative or the resolution of related issues.

Since the Minister of Transport and Regional Services' statement clarifying the roles and responsibilities for airspace management it has become apparent that, with the change in roles, CASA may not be in a position to implement all of their proposed airspace related safety actions. Consequently, there is the likelihood that there will be less safety enhancement of airspace than there previously might have been.

However, should Airservices Australia review the safety recommendations previously forwarded to CASA and the subsequent responses, during the development of the new airspace project, the knowledge gained from past air safety investigations has the potential to be retained. Consequently,
the ATSB would appreciate Airservices consideration and advice of any subsequent proposed action, of interim recommendation (IR) 19970155 issued on 30 January 1998 and the CASA response of 25 August 1999 (both attached).

Similarly, advice of any proposed action in regard to IR19960009, IR19980005 and IR19980059 issued to Airservices, where further action was also subject to CASA's Airspace 2000, would assist the ATSB in understanding the integration of safety lessons with future airspace developments.

Further correspondence
Date issued: 11 July 2000
Response from: AirServices Australia
Response status: Closed - Partially Accepted
Response text:

I apologise for the late response to your letter dated the 6th of December 1999, concerning the resolution of matters relating to the Airspace 2000 initiative. We note the recent statement by the Minister for Transport and Regional Services, and its effect in clarifying the roles and responsibilities for airspace management.

In the current airspace management arrangements, Airservices holds the legislative responsibility for the declaration of airspace in accordance with the ICAO "alphabet" menu of airspace. Responsibility for procedures applicable within airspace classes, including Class G airspace, together with ongoing training and pilot education remains with the Civil Aviation Safety Authority.

In that context, we believe that Recommendation IR19970155, relating to separation assurance in Class G airspace is more properly directed to CASA.

In relation to Recommendations IR19960009, IR19980005 and IR19980059, I offer the following advice.

IR19980005: Whilst Airservices disagrees in part with the investigation report, the recommendation is accepted.

Several initiatives have been undertaken to ensure that traffic information is facilitated to aircraft leaving controlled airspace for Class G airspace. For example, the Manual of Air Traffic services was amended in 1998 to require air traffic controllers to provide radar based traffic information to aircraft operating within 2000 feet of the base of controlled airspace.

The transitioning of low level Class G airspace services into TAAATS through 2000 will also significantly enhance the level of service provided to aircraft operating in, or transiting to Class G airspace. This will ensure not only the timely passing of traffic information, but through the utilisation of TAAATS capabilities, the passing of more relevant information than was previously available through Flight Service.

In relation to your statement regarding the integration of safety lessons with future airspace developments, Airservices is acutely aware of the primacy of safety in all aspects of our operations. In work being undertaken with industry to achieve reforms in the provision of services in low level airspace, detailed examination of hazards, potential mitigations, safety analysis and risk modelling are a fundamental part of our considerations. We would welcome the opportunity to provide you and your staff with a briefing on that reform program at your convenience.

 
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Last update 01 April 2011