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Interim Recommendation issued to: Airservices Australia

Recommendation details
Output No: IR19970027
Date issued: 10 September 1997
Safety action status: Closed
Background:

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.

Output text

The Bureau of Air Safety Investigation recommends that Airservices Australia:

1. review the wording in AIP/OPS RAC 32-33 para. 23.2.1.d. and MATS 4-8-1 to ensure that the pilot of an aircraft operating at or below FL125, and who has been assigned the responsibility to maintain visual separation from another aircraft, maintains continuous visual contact with that aircraft and immediately reports any loss of visual contact;

2. introduce the requirement for a controller to advise the crew of an IFR-category aircraft that the pilot of another aircraft has been assigned visual separation responsibility and to pass traffic information on the other aircraft; and

3. review MATS so that adequate guidance is provided in relation to utilisation of visual separation techniques.

Initial response
Date issued: 31 October 1997
Response from: AirServices Australia
Action status: Closed - Accepted
Response text:

I refer to your letter of 10 September enclosing Interim Recommendation 970027. The recommendations involve changes to pilot procedures in addition to those contemplated for ATS. As a result, Airservices will seek a review, in conjunction with CASA, of the visual separation standards applicable to aircraft operating below FL125, at the earliest opportunity. On completion of the review, BASI will be advised of any outcomes.

ATSB Note:

The Manual of Air Traffic Services amendment of 3 December 1998 in Separation Standards 4-5-1 paragraph 9 stated,

"In circumstances where an aircraft has been instructed to maintain separation from, but not follow, an IFR aircraft, traffic information shall be issued to the IFR aircraft, including advice that responsibility for separation has been assigned to the other aircraft".

This is in accordance with the interim recommendation.

 
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Last update 01 April 2011