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).
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.
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.
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.
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.
