British Aerospace Plc 3201 , VH-XFC 9 km NNE of Brisbane, 28 July 1999

1. The approach controller used the "sight and follow procedure" in an inappropriate circumstance. That is, the controller transferred the responsibility for separation to the pilot in a situation where the positive application of a separation standard may have been more appropriate.
2. The approach controller requested the crew of the Metroliner to sight the Jetstream in circumstances where a positive sighting may have been improbable.
3. The crew of the Metroliner sighted and followed the BAe 146 rather than the Jetstream

Notwithstanding the different profiles of the two aircraft, type identification of either aircraft would have been virtually impossible to determine at the ranges of the aircraft, that is beyond 6.8 NM. This is because contrast, which is the difference between the brightness of the aircraft against the brightness of the background, reduces with increasing range. Further, target identification would have been hampered by contour interaction. This phenomenon occurs where the outline of a target aircraft interacts with the contours present in the background. This is a particular problem at lower altitudes where aircraft appear against complex backgrounds.

When the crew of the Metroliner was instructed to report when they could see the other aircraft at 11 o'clock, the BAe 146 was the only aircraft discernible to them. With its side profile, the BAe 146 was at the extreme limit of visual acuity and could easily have been mistaken for a Jetstream, particularly as no other aircraft was in their field of vision. The Jetstream, with its head-on profile and greater range, would have been impossible to see at 9.8 NM. Moreover, because its actual position was not correctly described to the crew, they were looking for the Jetstream in the wrong place.

The approach controller may have realised that there was potential for mis-identification of the two aircraft. This is suggested by his action of cautioning the Metroliner crew about the BAe 146 that was on short final. However, the controller did not provide additional information that would have provided an assurance that the pilot was following the correct aircraft.

The identification of the potential conflict and action taken by the aerodrome controller was timely and appropriate. The vigilance and prompt action of the aerodrome controller acted as a safety defence to reduce the possibility of collision between the aircraft.

There were three aircraft in the approach sequence to land on
runway 19 at Brisbane: a British Aerospace 146 (BAe 146), VH-JJS,
on final at 2 NM; a British Aerospace Jetstream 3200 (Jetstream),
VH-XFC, on right base at 6.5 NM with approximately 8 track-miles to
touchdown; and a Fairchild SA226 Metroliner (Metroliner), VH-TFQ,
on an oblique left base at 6.5 NM with approximately 10.5
track-miles to touchdown. Analysis of recorded voice data confirmed
that the approach controller advised the crew of the Metroliner
that they were number 3 in the sequence and that the Jetstream was
number 2. Subsequent to that advice, the controller advised the
Metroliner crew that the aircraft they were to follow was at 11
o'clock, 10 NM at 1600 ft. They were instructed to report when they
could see that aircraft. The crew responded "Traffic sighted". The
crew of the Metroliner was then assigned responsibility for
separation from the Jetstream by being cleared to manoeuvre as
required to make a visual approach and to "follow the Jetstream".
In the same transmission, the crew were cautioned about the BAe 146
"on a very short final runway 19" and instructed to contact the
tower.

When the crew transferred to the tower frequency, the aerodrome
controller realised that the Metroliner was following the wrong
aircraft, the BAe 146, and could be in conflict with the Jetstream.
The controller instructed the Metroliner crew to orbit their
aircraft on left base to increase its separation with the
Jetstream. Analysis of recorded radar data indicated that
separation between the Metroliner and the Jetstream had reduced to
1.2 NM when they were at the same level.

The crew of the Metroliner did not recall being cautioned about
the 146. The aircraft they had sighted and followed was not the
Jetstream but the BAe 146, which resulted in the breakdown of
separation.

The Manual of Air Traffic Services (MATS) stated in MATS 4-5-1,
paragraph 7:

"Correct identification of the aircraft from which
separation must be maintained is essential".

Paragraph 10 stated:

"The traffic information provided shall contain as much
as is necessary of the following to assist the pilot in identifying
the other aircraft:

1. type, and description if unfamiliar;
2. level;
3. position information either by clock reference, bearing and
   distance, relation to a geographical point, reported position and
   estimate, or position in circuit;
4. intentions, or direction in flight."

Analysis of the radar data indicated that at the time the crew
was asked to report sighting the aircraft, the BAe 146 was in the
Metroliner's 11 o'clock relative position at 6.8 NM and displayed
an oblique, side profile. The position of the Jetstream was more to
the Metroliner's 12 o'clock relative position, at 9.8 NM and
displayed a head-on profile.