Infringement of separation standards, Williamtown Airport, VH-SDA

Sequence of Event¹

On 31 January 2005, a de-Havilland Canada Dash 8-202 (Dash 8)
aircraft that was inbound to Williamtown Airport, NSW, on a
scheduled passenger service from Brisbane, Queensland, passed
within 1 NM laterally and 300 ft vertically of the second of two
formations of two McDonnell Douglas Corporation F/A-18 (Hornet)
aircraft that were inbound to Williamtown Airport after a training
exercise. As the Dash 8 turned onto the base leg, the second
formation was about 6 NM north-west of Williamtown Airport, at
2,900 ft above mean sea level. The pilots of the Dash 8 descended
in response to a traffic alert and collision avoidance system
(TCAS) resolution advisory (RA) they received on that formation.
The approach controller did not provide the required separation
standard of 1,000 ft vertically or 3 NM laterally between the Dash
8 and the second formation. The tower controller² had not established
a visual separation standard between the aircraft at the time the
Dash 8 pilots received the RA. There was an infringement of
separation standards.

At about 1539:35^3,4 Eastern
Daylight-saving Time, the pilots of an Israel Aircraft Industries
Limited 1124A Westwind (Westwind) aircraft, that had been
participating in a military training exercise, contacted the tower
controller and advised that they were 7 NM to the north of
Williamtown Airport, tracking to join the circuit on a left base
leg for runway 12. At that time, the first formation of Hornet
aircraft had passed the initial point⁵ (Figure 1) for
runway 12, and the Dash 8 was in an early right downwind
position.

At 1540:10, the tower controller advised the pilots of the Dash 8
to conduct orbits to the south-west of the airfield at 2,500 ft.
However, the tower supervisor assessed that the Dash 8 could
continue on the downwind leg and advised the tower controller to
cancel the orbit instruction. At 1540:20, the tower controller
complied and instructed the pilots of the Dash 8 to continue on the
downwind leg. The tower supervisor had intended to position the
Dash 8 behind the first formation in the landing sequence.

Figure 1: Generic depiction of a military stream landing
circuit showing the location of the initial point (left circuit
depicted)

(adapted from the Manual of Air Traffic Services Pt 3 s3,
effective 10 June 2004)

At 1541:10, the tower controller instructed the pilots of the
Dash 8 to make a visual approach and to track for right base. At
1541:20, the tower controller instructed the pilots of the Westwind
to join the circuit via the upwind leg. In response to that
instruction, the pilots of the Westwind advised the tower
controller that the aircraft was 'minimum fuel'⁶. The tower
controller did not respond immediately to that broadcast and the
Westwind continued the approach via left base. At about 1541:30,
the radar data showed that the Dash 8 had already commenced the
turn onto the right base leg of the circuit. At that time, the
Westwind was established on left base. The Westwind pilots had
positioned their aircraft behind the first formation in the landing
sequence. In order to separate the Dash 8 and the Westwind, the
tower controller instructed the pilots of the Dash 8 to continue on
the downwind leg and that they were now to follow the Westwind.

At 1542, the tower controller advised the pilots of the Dash 8
that they could turn onto the base leg, when ready. At that time
the aircraft was close to the airspace boundary separating tower
and approach areas of responsibility, about 6.9 NM north-west of
the airport.

At 1542:20, the approach controller provided traffic
information, on the Dash 8, to the pilots of the second formation.
A review of the recorded radar data showed that, at that time, the
second formation was about 3 NM behind the Dash 8. Although the
investigation was unable to accurately determine the vertical
distance between the aircraft, from that radar data, it appeared
that there was about 100 ft between the second formation and the
Dash 8 when the approach controller provided traffic information to
the pilots of the second formation. The pilot of the lead aircraft
in the second formation advised the approach controller that he
could see the Dash 8.

The recorded radar data also showed that the altitude of the
Dash 8 increased from 2,500 ft on late downwind, to 2,900 ft as the
aircraft commenced the base turn, before descending in response to
the TCAS RA. The Dash 8 subsequently continued to descend for a
landing. At 1542:50, the second formation passed abeam the Dash 8,
when the Dash 8 was about to commence the turn onto the final
approach leg. At that time, there was 0.6 NM laterally between the
aircraft, and the Dash 8 was 300 ft vertically below the second
formation. The pilots of the Dash 8 advised the tower controller
that they had received an RA and that they were on a 'TCAS
descent'.

At 1543, the pilots of the second formation called the tower
controller and advised that they were at the right initial⁷ position. The tower
controller then realised that the second formation was inbound and
provided the pilots of the Dash 8 with traffic information on that
formation.

Minimum fuel

In accordance with the Royal Australian Air Force (RAAF)
Williamtown Standing Instructions, the Westwind was considered to
be a military aircraft while participating in military
exercises.

The copilot of the Westwind notified the tower controller that
the aircraft was 'minimum fuel' when the aircraft was on a left
base position for runway 12. The pilot in command of the Westwind
later reported that the aircraft was not 'minimum fuel', and that
the copilot had mistakenly made the 'minimum fuel' radio broadcast.
The operator of the Westwind advised that the declaration of
minimum fuel in that aircraft meant there was '…900 [pounds] or
less total fuel remaining at the Base Turn Point when in the
circuit, at an airport where a landing is assured'.

Air traffic control separation standards and
procedures

Control of aircraft in the Williamtown Airport terminal area was
provided by a tower controller using visual procedures and vertical
separation, and by an approach controller using radar and
procedural separation standards, in accordance with the Manual of
Air Traffic Services⁸ (MATS) and
local procedures. Coordination of control responsibilities was
required between the approach controller and the tower controller
in accordance with local procedures.

The required minimum vertical separation standard between the
Dash 8 and other aircraft operating in the Williamtown airspace was
1,000 ft.

In relation to the provision of aircraft separation, the MATS
4.1.1.4 stated that:

Tactical Separation Assurance places greater emphasis on traffic
planning and conflict avoidance rather than conflict resolution.
This is achieved through:

the proactive application of separation standards to avoid
rather than resolve conflicts;
planning traffic to guarantee rather than achieve
separation;
executing the plan so as to guarantee separation; and
monitoring the situation to ensure that plan and execution are
effective.

The tower controller cleared the pilot of the Dash 8 for further
descent on a visual approach when the aircraft was in a late
downwind position. A visual approach authorised the pilots to
continue descent visually for a landing. A review of the recorded
radar data showed that the Dash 8 maintained 2,600 ft for about 1.5
minutes on the downwind leg of the circuit. It reached a minimum
altitude of 2,500 ft, on descent, when the aircraft was on a late
downwind position, and climbed to 2,900 ft as it turned onto the
base leg.

The Aeronautical Information Publication (AIP) advised pilots
that they must report to ATC 'when the aircraft has left a level at
which level flight has been conducted in the course of climb,
cruise or descent'. The pilot in command of the Dash 8 did not
recall climbing the aircraft from 2,500 ft on the downwind leg to
2,900 ft on the base leg of the circuit.

Approach control

At Williamtown Airport, the approach controller was responsible
for providing an air traffic control service between instrument
flight rules (IFR) category aircraft in accordance with the MATS
and local procedures. That included ensuring that a separation
standard existed between arriving IFR aircraft, and providing an
orderly flow of arriving aircraft.

There was an approach controller and a supervisor rostered in
the Williamtown approach control unit at the time of the
occurrence. Both positions were staffed by an appropriately rated
military air traffic controller (ATC). The approach controller had
about 6 years experience as an ATC, and had been rated in the
approach radar position at Williamtown Airport for 6 months. The
approach supervisor was responsible for the supervision of the
approach control unit at Williamtown Airport. He had considerable
experience as an ATC, and had held a rating in approach control at
Williamtown Airport for about 18 months.

A review of the recorded radar data showed that, at the time the
approach controller cleared the pilots of the second formation to
descend to 3,000 ft, the second formation was approximately 27 NM
from the airport, with about 32 NM to fly to land. Had the pilots
of the Dash 8 not been instructed to extend the downwind leg, the
Dash 8 would have had about 6 to 8 NM to fly to touch down. The
assignment of 3,000 ft to the pilots of the second formation did
not provide either a vertical separation standard, or separation
assurance, between the second formation and the Dash 8 in the
circuit. The approach controller was not concerned about the
separation between the Dash 8 on the downwind leg, and the second
formation on descent to 3,000 ft, because of the distance the
second formation was from the airfield at the time the approach
controller issued the descent clearance.

The normal circuit direction at Williamtown Airport, on runway
12, was right. Military aircraft would track from the initial point
along the dead side⁹ of the circuit
and turn right, into the circuit, once the pilot saw the other
traffic operating in the circuit (see Figure 1). The approach
controller cleared the Westwind to enter the circuit via a
non-standard left base leg and to descend on a visual approach.

The tower controller was required, by local procedures, to
advise the approach controller when the Dash 8 pilots were cleared
to descend on a visual approach.

On receipt of that advice, the approach controller removed the
Dash 8's flight progress strip¹⁰
from the flight progress board¹¹.
Although the aircraft was still visible to the approach controller
on the situation data display (SDD)¹², the potential for
an infringement of separation standards was no longer presented to
the approach controller on the flight progress board. The approach
controller later reported that the flight progress strip was
removed from the board because there was an expectation that the
second formation would remain clear of the Dash 8 in the
circuit.

Tower control

The tower cabin was equipped with an SDD that provided the tower
controller with the same display of air traffic that was provided
to the approach controller. The MATS addressed the use of tower
radar in an aerodrome control service. It stated that the tower
radar display was available for the determination of the altitude,
position or tracking of an aircraft to establish or monitor
separation. However, the MATS also stated that:

…the use of the tower radar should not impinge upon an aerodrome
controller's primary function of maintaining a visual observation
of operations on and in the vicinity of the aerodrome.

There were three operational control positions established in
the control tower; a supervisor position, a tower control position
and a surface movement control position. Each position was staffed
by an appropriately rated military ATC. The supervisor and the
tower controller each had 18 months tower control experience. The
control tower was also a training environment at the time of the
occurrence. There was a controller-under-training in each of the
three control positions. Each rated military controller, in each of
the positions, was also a qualified training officer.

The supervisor was responsible for airspace management and
operations on the airport. The supervisor had the authority to
assess and amend the decisions of the tower controller and the
surface movement controller if required. Unless the tower
controller considered that such intervention compromised safety,
the tower controller was obliged to comply with the decisions of
the supervisor.

The first formation joined the circuit on a right crosswind leg
on descent from 1,500 ft. Once the tower controller was able to
apply a visual separation standard between the Dash 8 and that
formation, the tower controller instructed the pilots of the Dash 8
to descend on a visual approach.

The tower controller was also required to notify the approach
controller of any aircraft that were extending towards the
aerodrome traffic zone (ATZ) lateral boundary which was the lateral
boundary of tower airspace¹³.
Neither the tower controller nor the supervisor advised the
approach controller that the Dash 8 was extending downwind, and
would be turning onto the base leg in the vicinity of the lateral
boundary of the ATZ. The approach controller was not expecting to
see the Dash 8 in that position. The approach controller observed,
on the SDD, the Dash 8 turning onto the base leg of the circuit in
the vicinity of the lateral boundary of the ATZ, and in the
vicinity of the second formation.

The approach controller immediately provided traffic information
to the pilots of the second formation about the Dash 8, but could
not provide traffic information to the Dash 8 pilots as they were
operating on the tower frequency.

The tower controller later reported that he originally intended
to instruct the pilots of the Dash 8 to remain in the downwind
position at 2,500 ft because it enabled him to better regulate the
circuit traffic, especially given that he was instructing a
controller-under-training at the time.

Instructing pilots to maintain 2,500 ft on the downwind leg was
a common practice at Williamtown Airport. The AIP En Route
Supplement Australia (ERSA) advised that all civil aircraft
operating at Williamtown Airport were required to carry 30 minutes
holding fuel. The tower controller later reported that that holding
fuel enabled Williamtown air traffic control the flexibility to
hold civil aircraft for up to 30 minutes, if necessary, for
sequencing with arriving military aircraft.

Australian Defence Air Traffic System
(ADATS)

Air traffic controllers at Williamtown Airport used the
Australian Defence Air Traffic System (ADATS) to control aircraft
operating within the Williamtown airspace. The ADATS associated a
flight plan to an allocated transponder code¹⁴ and displayed that
information to the controller as a data block, attached to the
aircraft track symbol, on the SDD.

The data block could either be a full or limited data block. The
full data block was white and included the call sign, altitude and
radar derived ground speed, of airborne aircraft equipped with a
serviceable transponder. It could also include other control
information entered by a controller. A code and flight plan
remained associated for a predetermined period of time depending on
the nature of the flight. Once that time expired, the code/flight
plan association terminated and the data block presented to the
controller became a limited data block. The limited data block
format did not display the call sign, and the colour of the data
block changed from white to green. The limited data block format
displayed an aircraft's allocated transponder code, altitude and
radar derived ground speed.

The colours allocated to the track symbol and data block
indicated the relevance of that aircraft to controllers. A green
data block normally indicated that the aircraft was no longer of
concern to the controller, as the flight plan was no longer active.
The data block and track symbol colours assisted controllers with
situational awareness.

The information displayed to the approach controller was also
displayed to the tower controllers on the tower SDD. All
information on relevant inbound, locally-based, military aircraft
was displayed in the aircraft data block, including sequencing and
tracking information. In accordance with local procedures, while a
flight plan was associated with a specific transponder code, there
was no requirement for the approach controller to provide voice
coordination to the tower controller.

That applied to locally-based, military aircraft, as that
information was available on the tower SDD. The tower controller
was required to scan the SDD to determine the sequence and tracking
details of arriving locally-based military aircraft. Tower
controllers relied on the accuracy of the information presented in
the data block, including the colour and sequencing instructions,
to assist them in determining an estimated time of arrival, the
arrival sequence and the inbound route of each aircraft.

Controllers reported that occasionally the code/flight plan
association terminated while aircraft were still airborne. In those
circumstances, in accordance with local procedures, the approach
controller was required to use voice coordination to advise the
tower controller about relevant inbound aircraft. The tower
controller would not necessarily detect an inbound aircraft on the
SDD if the code/flight plan association had terminated, unless
voice coordination was received from the approach controller.

The code/flight plan association for the second formation
terminated as the formation tracked to the circuit area and the
data label changed colour from white to green. The approach
controller reported that, as the termination occurred close to the
circuit area, the tower controller would already have been aware
that the formation was inbound. As a result, no voice coordination
was provided to the tower controller.

Meteorological information

The weather was reported as fine and clear and was not
considered to have been a factor in the occurrence.

Only those investigation areas
identified by the headings and subheadings were considered to be
relevant to the circumstances of the occurrence.
A tower controller employed by the
Department of Defence provides a similar air traffic control
service as a civil aerodrome controller.
The 24-hour clock is used in this
report to describe the local time of day, Eastern Daylight-saving
Time, as particular events occurred. Eastern Daylight-saving Time
was Coordinated Universal Time (UTC)+ 11 hours.
Due to the limitations with the
audio recording, all times are accurate to within about +/- 5
seconds.
The initial point for runway 12 at
Williamtown Airport was located about 4 NM from the threshold of
runway 12 along the extended centreline of taxiway Alpha, at 1,500
feet above mean sea level.
This phrase is used to advise air
traffic control that the pilot requires priority for landing based
on the amount of fuel remaining, calculated at a particular stage
of flight (Manual of Air Traffic Services, pt 10, effective 9 June
2004).
The left, right and straight initial
positions are 30 seconds prior to the initial point with wings
level.
The Manual of Air Traffic Service is
a joint civil/military publication used by Department of Defence
and Airservices Australia air traffic controllers.
The dead side of the circuit is the
side of the airfield or active runway, opposite to that of the
circuit pattern in use, and from which arriving aircraft joining
the circuit.
A flight progress strip is a thin
cardboard strip used to record flight data relating to control of
an aircraft.
A flight progress board is a piece
of equipment used to display flight progress strips. Controllers
use the information on the flight progress board to assist in
managing the traffic situation.
The situation data display was an
electronic display of radar derived information that depicted the
positions and movements of aircraft.
The ATZ is that airspace within 5
NM of the tactical air navigation equipment ground based navigation
aid, over land, from ground level to 1,500 ft above mean sea level.
At Williamtown Airport, the stream landing circuit pattern (see
Figure 1) is contained entirely within the ATZ.
A transponder is a
receiver/transmitter which will generate a reply signal upon proper
interrogation, in this case, of a signal generated by a ground
based transmitter/receiver.

SAFETY ACTION

Safety Advisory Notice 20060014

The Australian Transport Safety Bureau suggests that the
Department of Defence distributes this report widely among
controllers so that supervisors are aware that intervention in
separation and sequencing at the tactical level has the potential
to adversely affect the situational awareness of the controllers
under their supervision. Further, they must be prepared to take
control of a situation if necessary until the controller is able to
safely resume responsibility for separation.

Safety Advisory Notice 20060015

The Australian Transport Safety Bureau suggests that the
Department of Defence ensures that controllers are aware of the
importance of the separation assurance provisions of MATS
4.1.1.4.

CONCLUSIONS

Significant factors

The approach controller did not assign an altitude to the
second formation that provided a vertical separation standard
between the second formation and the Dash 8.
The tower supervisor advised the tower controller to cancel the
instruction to the Dash 8 pilots to orbit on the downwind leg of
the circuit at 2,500 ft, and to continue on the downwind leg of the
circuit.
The tower controller was not aware that the second formation
was inbound to the circuit.
The tower controller did not notify the approach controller
that the Dash 8 was extending towards the lateral boundary of the
ATZ.
The pilots of the Westwind did not join the circuit via the
upwind leg as instructed by the tower controller.

Contributing factors

The code/flight plan association on the ADATS data block of the
second formation terminated.
The approach controller removed the second formation's flight
progress strip from the flight progress board.
The approach controller did not provide the tower controller
with voice coordination on the second formation once the
code/flight plan association terminated.
The pilots of the Westwind incorrectly notified the tower
controller that their aircraft was 'minimum fuel' when the aircraft
was on left base.
The tower controller and the tower supervisor were relatively
inexperienced and each had responsibility for a
controller-under-training.

ANALYSIS

Introduction

The tower controller and the approach controller were unable to
continue to apply a separation standard between the second
formation of Hornets and the Dash 8. This analysis examines the
development of the occurrence and highlights the safety issues that
became evident as a result of the investigation.

Air traffic control separation standards and procedures

The approach controller's assignment of 3,000 ft to the pilots
of second formation of Hornets when they had about 32 NM to fly to
land, did not provide either a vertical separation standard or
separation assurance between the second formation and the Dash 8.
That action precipitated the sequence of events that followed.
While a radar separation standard existed initially between the
Dash 8 and the second formation, it relied on continuous monitoring
by the approach controller. The allocation, by the approach
controller, of an altitude to the second formation that would have
provided the 1,000 ft vertical separation standard with the Dash 8
would have assured that a separation standard continued to exist.
It would also have given the tower controller the option to assign
further descent to the pilots of the second formation once a visual
separation standard between the second formation and other aircraft
joining the circuit could be applied.

The approach controller was required to establish a separation
standard between the second formation and the Dash 8, and to have
that standard in place before transferring the responsibility for
separation to the tower controller. In not providing separation
assurance between the second formation and the Dash 8, the approach
controller did not demonstrate 'the proactive application of
separation standards to avoid rather than resolve conflicts' as
stated in the Manual of Air Traffic Services (MATS).

It was likely that the limited data block format displayed on
the second formation adversely affected the situational awareness
of both the tower controller and the tower supervisor at the time
the tower controller advised the pilots of the Dash 8 that they
could turn base 'when ready'. The tower controller did not provide
traffic information about the location of the second formation to
the pilots of the Dash 8 until after the pilots of the Dash 8
advised that they were on a traffic alert and collision avoidance
system descent. At the time the tower controller instructed the
pilots of the Dash 8 to turn base the second time, the relative
locations of the second formation and the Dash 8 placed the
aircraft in potential conflict. That would have been apparent to
both the tower controller and the tower supervisor had either of
them been aware of the location and intentions of the second
formation at that time.

The traffic situation in the circuit area became quite complex
in a very short period of time. The relative inexperience of the
tower controllers may have limited their ability to realise the
potential for a relatively simple inbound sequence to develop into
an infringement of separation standards.

Communication between the tower controller and the tower
supervisor may have been difficult due to the complexity of
communication between trainees and their training officers, and
between controllers in the various control positions in the tower.
Had the Dash 8 remained at 2,500 ft conducting orbits in the
downwind position as initially instructed until the tower
controller could fit that aircraft into the landing sequence, there
may have been more time for the tower controller to:

liaise with the tower supervisor
regulate the flow of traffic
identify the second formation on the situation data display
(SDD)
assess options that may have ensured that separation continued
to exist
evaluate the impact of the late declaration of 'minimum fuel'
by the pilots of the Westwind
provide traffic information where appropriate
issue alternative instructions.

Once the tower controller notified the approach controller that
the Dash 8 had been assigned a visual approach, the approach
controller removed the flight progress strip from the flight
progress board. After that, there was nothing to prompt the
approach controller to critically re-evaluate the information on
which the original evaluation, that the aircraft would not come
into close proximity, was made, even though there remained a
possible confliction between the inbound second formation and the
Dash 8.

Although the decision by the tower supervisor to instruct the
pilots of the Dash 8 to continue on the downwind leg of the circuit
and not conduct the left orbit in the downwind position may have
been appropriate, it unnecessarily increased the complexity of the
traffic scenario, especially given the training workload in the
tower at that time. It also reduced the options available to the
tower controller once the Westwind joined the circuit on the left
base leg rather than via the initial point, or the upwind leg of
the circuit as instructed. The instruction issued to the pilots of
the Westwind by the tower controller to enter the circuit via the
upwind leg would have provided the Westwind with adequate priority
and would not have compromised the safety of the flight. That may
also have created an opportunity for the tower controller to locate
the second formation on the SDD and therefore reduce the likelihood
of an infringement of separation standards.

Tower supervisors have the authority to become involved with
tactical air traffic control decisions and may assume control
responsibility for sequencing or separation, without formally
taking over from the tower controller. Tower supervisors must
consider how an instruction to the tower controller might affect
the situational awareness of that controller. A supervisor must be
prepared to take control of the situation, in which they have
intervened at a tactical level, until the tower controller can
resume responsibility for separation. Otherwise tower controllers
may inherit a scenario from the tower supervisor that they may not
entirely understand, with little time to react.

Although the extended downwind of the Dash 8 resulted from the
Westwind not complying with a control instruction, the tower
controller was required to notify the approach controller that the
aircraft was extending and may track beyond the lateral boundary of
the Aerodrome Traffic Zone (ATZ). The tower controller did not
notify the approach controller that the Dash 8 was extending
downwind. Therefore, the approach controller was unaware that the
Dash 8 was tracking towards the right initial point, in potential
conflict with the second formation.

Minimum Fuel

Military air traffic controllers are familiar with pilots
declaring 'minimum fuel' and with their responses in such
circumstances. However, the disposition of the Westwind relative to
base and final, the relatively complex nature of the traffic
pattern at the time of the broadcast, and the training environment
that existed in the control tower at the time of the occurrence,
all reduced the time available for the controller to consider the
impact of the 'minimum fuel' broadcast on the traffic pattern.

By the time the tower controller had an opportunity to assess
the impact that that transmission may have on the landing sequence,
and to determine what priority could have been provided to the
pilots of the Westwind, the Westwind was already on the final
approach leg. The pilots of the Westwind did not comply with the
instruction by the tower controller to join the circuit on the
upwind leg, even though that would have been acceptable in such
circumstances. The declaration of 'minimum fuel' in such close
proximity to the landing threshold may have distracted the
controllers in the tower and reduced the effectiveness of their
scans of the tower environment, including the SDD, and added to the
complexity of the situation.

Australian Defence Air Traffic System (ADATS)

The approach controller did not provide the tower controller
with information on the second formation after the code/flight plan
association for that formation terminated. Although the approach
controller reported that the termination occurred close to the
boundary of tower airspace, the tower controller appeared to be
unaware of the proximity of the second formation. Had the approach
controller provided the tower controller with coordination on the
second formation, in accordance with local procedures, the tower
controller's attention would have been drawn to the location of
that formation on the SDD. That may have given the tower controller
an opportunity to ensure that the Dash 8 remained clear of the
inbound path of the second formation.

On 31 January 2005, a de-Havilland Canada Dash 8-202 (Dash 8)
aircraft that was inbound to Williamtown Airport, NSW, on a
scheduled passenger service from Brisbane, Queensland, passed 0.6
NM laterally and 300 ft vertically by the second of two formations
of two McDonnell Douglas Corporation F/A-18 (Hornet) aircraft that
were inbound to Williamtown Airport after a training exercise. As
the Dash 8 turned onto the base leg, the second formation was about
6 NM north-west of Williamtown Airport, at 2,900 ft above mean sea
level. The pilots of the Dash 8 descended in response to a traffic
alert and collision avoidance system resolution advisory (RA) they
received on that formation. The approach controller did not provide
the required separation standard of 1,000 ft vertically or 3 NM
laterally between the Dash 8 and the second formation. The tower
controller had not established a visual separation standard between
the aircraft at the time the Dash 8 pilots received the RA. There
was an infringement of separation standards.

The investigation found that the factors that contributed to the
occurrence included:

The approach controller did not assign an altitude to the
second formation that provided a vertical separation standard
between the second formation and the Dash 8
The tower supervisor advised the tower controller to cancel an
instruction to the Dash 8 pilots to orbit on the downwind leg of
the circuit at 2,500 ft, and to continue on the downwind leg of the
circuit
The tower controller did not notify the approach controller
that the Dash 8 was extending towards the lateral boundary of tower
airspace
The pilots of a Westwind incorrectly notified the tower that
their aircraft was 'minimum fuel' and did not join the circuit via
the upwind leg as instructed by the tower controller.