SUBJECT
Visual Separation Procedure - Provision of Traffic Information by
ATC
OCCURRENCE SUMMARY
During an instrument training exercise at Darwin, a Partenavia
(P.68C) was tracking from the west to overhead the Bagot Locator
(BGT L) to fly a runway 11 locator approach. As the P.68C
approached overhead the airfield, a B767 was backtracking along
runway 29 for a Darwin IKUMA ONE standard instrument departure
(SID). The air traffic controller advised the P.68C pilot of the
B767 departure details and questioned whether he could maintain his
own visual separation with the B767. Following an affirmative
reply, the controller assigned separation responsibility to the
pilot of the P.68C. The controller then explained to the pilot of
the P.68C the expected track of the B767 after takeoff. Following
an acknowledgment from the P.68C, that aircraft was instructed to
make the locator approach and to maintain 3,000 ft.
On departing runway 29 the B767's terrain collision avoidance
system (TCAS) indicated a target 1,800 ft above and on the intended
SID track. As the B767 climbed, the TCAS indicated a rapidly
closing target with a vertical separation reducing to 800 ft. The
B767 crew sighted the P.68C and maintained runway heading to avoid
further conflict. When clear of the target, the B767 was turned
right to intercept the 294 very high frequency omni-directional
(VOR) radial. The B767 captain reported that throughout the takeoff
and initial climb, neither the tower nor the departures controller
gave traffic information, until the traffic conflict report was
reported by the B767 pilot.
SAFETY DEFICIENCY
In accordance with the manual of air traffic services (MATS) 4-8-1
para. 1c, a pilot who is operating at or below FL125 and who
reports sighting another aircraft can be instructed to maintain
visual separation from that other aircraft. However, neither the
aeronautical information publication (AIP) nor MATS requires the
crew of the other aircraft to be informed that a visual separation
standard between their aircraft and another has been activated. In
this instance, the crew of the B767 were unaware that visual
separation was being applied between their aircraft and the
P.68C.
ANALYSIS
The B767 captain's air safety incident report (ASIR) questions the
concept of allowing the pilot of one aircraft to sight and then
maintain a visual separation with another aircraft without the
pilot of the other aircraft knowing that the separation standard
has been applied to his aircraft. In accordance with MATS 4-8-1
para 1c, a pilot operating at or below FL125 having reported
sighting an aircraft can be instructed to maintain visual
separation with that aircraft. Discussions with aviation industry
personnel indicate that many captains of high - volume passenger
carrying aircraft are either reluctant to use or do not understand
the procedures applicable to visual separation standards. Their
main concern is that the responsibility for the separation standard
between their aircraft and another aircraft is being vested in the
pilot of the other aircraft, without their being aware of the other
traffic.
In this instance, the controller checked with the P.68C pilot to
confirm that he could maintain a visual separation with the B767.
When this was confirmed, the controller asked the P.68C pilot how
the separation could be maintained. In accepting that the P.68C had
an additional pilot (a check captain) on board the controller
instructed the pilot of the P.68C to make the runway 11 locator
approach, restricting the descent profile of the P.68C by
maintaining 3,000 ft. However, the outbound leg of this approach
for a CAT A aircraft is 300 degrees magnetic with a left tear-drop
turn inbound to track 105 degrees magnetic. The descent is
commenced 2.5 minutes after passing overhead the BGT L.
The B767 was departing on runway 29, the opposite direction to the
inbound leg of the runway 11 locator approach, and was facing into
the afternoon sun, making it difficult to observe other aircraft in
the western sector. Neither the report from the B767 captain nor
the controller's report specified the position of the P.68C when
the B767 became airborne. However, the B767 captain stated that
after rotation, TCAS indicated a target 1,800 ft above and on his
intended SID track. Shortly after, the TCAS indicated that the
target was rapidly closing with a vertical separation of 800 ft.
The report added that if the B767 had been turned right to
intercept the 294 radial (as was required in the SID), a serious
traffic conflict would have resulted.
There was no vertical restriction applied to the departing B767,
only the requirement for the P.68C crew to maintain visual
separation. The ASIR from the B767 captain indicated that he was
unaware that it was no longer necessary to have both aircraft sight
each other in order to establish a visual separation standard (MATS
4-8-1 para. 1c refers). He further stated that it was unacceptable
to have a light aircraft which had the B767 in sight solely
responsible for the maintenance of the visual separation
standard.
As air traffic densities increase and airspace management becomes
increasingly more complex, the use of TCAS in aircraft will be more
widely accepted as an important defence mechanism in the prevention
of airborne collisions. More recently, the aviation industry has
noted the increasing numbers of potential accidents which are being
prevented by the use of TCAS. Effectively, TCAS provides the crew
of an aircraft with an electronic monitoring capability of other
aircraft in proximity to their aircraft and their intended flight
path. It follows that a lack of information regarding aircraft
which may be entitled to operate in close proximity (that is, with
less than standard instrument flight rules (IFR) separation) could
cause crews to deviate unnecessarily from their clearance.
Therefore, the provision of traffic information and advice
concerning the use of the procedure will increase a crew's
situational awareness and assist them in making appropriate
decisions for the safe conduct of the flight.
