Local safety action
As a result of the investigation, Airservices Australia has:
- Introduced a revised missed approach procedure on 17 June 1999.
This procedure changed the outbound heading from 030 degrees to 015
degrees, and - Introduced Cairns Local Instruction TLI99/105 which restricted
the available headings for departures to 030 degrees only, when
missed approaches are likely.
The combined effect of these actions was to provide a nominal 15
degree buffer between the departure and missed approach paths.
Airservices Australia management at Cairns has introduced a
program of regular in-flight emergency response and abnormal
situation refresher training for tower staff. The first course was
completed between 19 - 23 July 1999.
Recommendation
As a result of the investigation the Australian Transport Safety
Bureau (formerly Bureau of Air Safety Investigation) issued the
following recommendation to Airservices Australia on 23 December
1999:
R19990227
That Airservices Australia review ongoing refresher training for
all staff. In particular, to ensure that adequate discussion and
simulation of unusual situations pertinent to specific locations is
included in the syllabus.
Airservices Australia responded on 7 February 2000 accepting the
recommendation.
The Australian Transport Safety Bureau classified the response
as CLOSED - ACCEPTED
- The geographical restraints of high terrain surrounding the
Cairns aerodrome required all aircraft movements in instrument
meteorological conditions to proceed into a 40 degree sector of
airspace. - The Cairns runway 15 missed approach and departure procedures
required all aircraft to turn into the same narrow sector of
airspace. - The weather conditions were such that missed approaches were
likely and that the aerodrome controller would not be able to
provide visual separation. - The departure instructions for the Cessna placed that aircraft
into a direct track conflict with the runway 15 missed approach
path. - The aerodrome controller's decision not to increase the cut-off
distance beyond 8NM resulted in a reduction of the safety buffers
in the separation plan. - The aerodrome controller's separation plan relied on the
performance of the Cessna being sufficient to climb above the
Shorts. - The performance of the Cessna was not as good as that expected
by the aerodrome controller. - The weather conditions encountered by the Cessna were such that
the pilot needed to reduce the fair weather climb performance for
operational safety reasons. - The coordination between the aerodrome controller and the
approach controller was inadequate. - The Cairns Local Instructions did not authorise the use of
radar by the aerodrome controller for separation purposes. - Neither the aerodrome controller nor the approach controller
applied positive separation assurance techniques. - Cairns tower controllers had not received adequate ongoing
refresher training in emergency and/or unusual situations.
Weather
The general conditions of low cloud and heavy rain made any
visual reference unlikely for both pilots and controllers. As both
crews were operating in instrument flying conditions, the chances
of their making visual contact with the other aircraft were low.
Therefore, the presence of a break in the cloud of sufficient size
to allow such sighting was of a fortuitous nature and could not be
relied on for tactical planning purposes.
Missed approach and departure procedures
These procedures were so constrained by terrain considerations
that, whenever an aircraft commenced a missed approach, a conflict
would occur unless the aerodrome controller could visually monitor
the aircraft with any departure until a specific separation
standard was achieved.
Even using the 030 degrees heading option for the departure, the
missed approach procedure would have, at best, resulted in the
aircraft tracking parallel to each other approximately 1 -1.5 NM
apart; a situation that would still result in an infringement of
separation standards if no vertical separation existed. As the
terrain prevented a departure heading east of 030 degrees, the
situation would have required the missed approach track to be north
west of 030 degrees to guarantee a divergence.
Air traffic control procedures
MATS 6-4-3 allowed an unrestricted departure prior to an
arriving aircraft commencing final approach provided a specific
lateral separation standard of a minimum of 45 degrees between the
departure track and the reciprocal of the final approach track
existed. If the departure heading had been between 015 and 030
degrees, this standard would have been achieved. However, because
of the limitations of the missed approach track and the weather
situation, the maintenance of the separation standard could not be
expected and an alternative standard would need to be
established.
MATS also allowed for a departure when an aircraft had commenced
final approach provided a reasonable assurance existed that a
landing could be accomplished or that separation standards could be
applied between the aircraft in a missed approach and the aircraft
desiring take-off clearance. In this case the weather precluded any
guarantee of the Shorts landing and no separation assurance was in
place.
It may have been possible to use the lateral separation standard
of 45 degrees between tracks if the departure heading had been
between 015 - 030 degrees. However, even if this option had been
taken, MATS required an allowance to be made when, among other
things, missed approaches were likely, and/or, a faster aircraft
was approaching in respect of a slower aircraft taking off. Both
circumstances applied to this occurrence.
Cairns Local Instructions (TWR - 29) gave further guidance in
the specific case of runway 15 when "... consideration must be
given to increase the cut-off distance used between the landing
aircraft; and the aircraft commencing takeoff." Because the Shorts
was between 9 - 7.5 NM during the time that the Cessna was
processed for departure, some doubt existed as to which
circumstance applied. In either case the departure was conditional
on a separation standard being applied and, as the heading issued
was not 45 degrees from the approach track, neither of the lateral
separation standards were useable.
As the aircraft were on conflicting tracks without any vertical
separation established, a radar vector may have been appropriate.
The approach controller was rated to perform the task but did not
have either crew on frequency. The aerodrome controller had the
radio contact but was not rated to perform the task. However, as
the aircraft came into close proximity, an emergency radar vector
by the aerodrome controller may have increased the minimum distance
between the aircraft. MATS 4-1-1 para 3.f authorises any controller
to take any necessary action to ensure aircraft safety.
Separation standards
Procedural lateral separation with the final approach path was
possible under the provisions of MATS but not under the terms of
the departure instructions issued by the approach controller. As
the tracks of both aircraft were not laterally separated (a
situation that became a direct conflict when the Shorts commenced a
missed approach) an alternative form of separation was
required.
The aerodrome controller may use visual separation based on
judgement and experience to provide initial separation until a more
specific standard is achieved. However, in the prevailing weather
conditions adequate visual contact with both aircraft was not
possible. Therefore, this standard was not appropriate.
Radar separation of 3 NM was not appropriate as the conflict
occurred within 2 NM of the aerodrome. In addition, as both
aircraft were heading in the same sector of airspace, the
likelihood was that the standard would not be achieved for some
time. Longitudinal standards were also unlikely to be attained in
the short term for similar reasons.
Vertical separation was applicable but relied on the Cessna
becoming established 1,000 ft above the Shorts. As the Cessna was
starting from a position below that of the Shorts, the standard was
not available during the initial climb phase. A standard of 500 ft
was useable initially as a form of emergency separation. However,
the limitations were the same as for the 1,000 ft standard.
There was an option to amend the departure heading for the
Cessna to provide initial lateral separation; the limitations of
this option have been discussed above. Consequently, no separation
standard existed at the time the Cessna departed and separation
assurance was neither achieved nor positively sought until the
conflict was unavoidable.
Aircraft performance
Although the aerodrome controller expected the Cessna to
out-climb the Shorts, operational factors were such that the
opposite was the case. MATS 4-1-1 paragraph 13 informed controllers
of such a possibility. In addition, in the case of the Cessna,
several factors in the first 4 minutes of flight indicated that
operations were not as expected.
Aerodrome controller
The controller had a traffic management plan that relied on an
expected aircraft performance of the Cessna and Shorts types. This
expectation was based on his observations since arriving at Cairns.
The plan was twofold; either the Cessna would out-climb the Shorts
and vertical separation would be established, or the Cessna would
reach the point at which the missed approach track would conflict
with the departure track first and pass clear of that point before
the Shorts entered the area of conflict. There was no consultation
with the approach controller and no discussion of any alternative
plan even though the weather conditions precluded visual separation
as an initial standard.
As the flight of the Cessna progressed, the controller realised
that the climb was not as good as expected but elected to continue
with his original plan hoping that one of the alternatives would
still work. Separation assurance had not been implemented.
When the crew of the Shorts reported maintaining 1,000 ft the
controller established that the Cessna had left 1,500 ft, thus
indicating a 500 ft emergency separation standard. However, no
instruction was issued to the crew of the Shorts other than a climb
to 1,500 ft. Additionally, the poor quality of the radio
transmission and the mention of 1,500 (ft) by the crew should have
raised sufficient doubt in the controller's mind to warrant
clarification.
Although the aerodrome controller considered that the radar
altitude read-out from the SD36 was erratic, other controllers
expressed concern over the fact that they saw the altitudes of the
aircraft indicate similar levels as they approached the point of
closest proximity. When the approach controller questioned the
separation status, albeit with an oblique comment, the reply was
that there was "not much to do mate, ..." indicating that he had
done all that was required, even though no separation standard had
been achieved. However, a few seconds later he issued updated
traffic information to the crew of the Shorts indicating that the
other aircraft was in the same position at the same level.
The passing of traffic information when an aircraft is in cloud
and heavy rain and the crew are flying the aircraft with reference
to instruments, was unlikely to result in a sighting; even though
it did in this case. However, passing traffic information when a
near collision is imminent is sound practice.
Approach controller
The controller had been surprised when he realised that the
aerodrome controller had cleared the Cessna for take off ahead of
the arriving Shorts. He realised that if a missed approach
resulted, then a conflict was imminent. He assumed that the
aerodrome controller had accepted separation responsibility and
chose to allow him to continue with that role but made no attempt
to establish what standard was being used. Even though the last
known information was that the Shorts was likely to conduct a
missed approach and visual separation was unlikely, no coordination
was instigated to adequately determine the status of separation in
his airspace.
Other controllers reported that as the situation developed, they
had asked what was happening and made comments such as "do
something". The reply was that the aerodrome controller was
providing the separation. Eventually he could see that the radar
indicated a near collision situation and questioned the aerodrome
controller, but this was with very ambiguous words and when the
aircraft were only 10 seconds from the point of closest
proximity.
Training
The circumstances surrounding the occurrence were not often
experienced at Cairns. Consequently, the combination of events were
such that many controllers had never seen this scenario before and
were not fully familiar with how to resolve the confliction. The
procedures were such that this type of incident could have happened
at any time in recent years.
Although initial training covered the procedures contained in
Local Instructions, some controllers could not remember any recent
"Team" discussions on unusual or emergency situations and formal
abnormal situation refresher training had not been regularly
undertaken.
Pilot of the Cessna
Operational decisions were taken with the safety of the flight
in mind and as a result of the prevailing weather conditions; the
full effect of which were not known until actually encountered.
The pilot had intended to comply with the departure instructions
as he commenced take-off roll but found himself unable to continue
with that plan as a result of constant turbulence and
downdrafts.
Crew of the Shorts
The crew had made a standard missed approach decision and the
pilot in command had intended to maintain the aircraft at 1,000 ft
initially. However, the instruction to the co-pilot was made at the
same time as the pilot in command was broadcasting to air traffic
control. The words were heard by the aerodrome controller but not
by the co-pilot. This situation led to a misunderstanding, in that
the controller thought the aircraft was going to maintain 1,000 ft
but the crew continued to climb to their assigned level of 1,500
ft.
Sequence of events
The Short Bros SD 3-60-300 (Shorts) was being radar vectored by
air traffic control for an instrument landing system (ILS) approach
to runway 15 at Cairns.
The weather conditions were fluctuating about the landing minima
with low cloud and rain passing through the local area in general
"stream" conditions. The automatic terminal information service was
quoting a cloud base of 1,000 ft with lower patches and visibility
reduced to 5,000 m in passing showers. The conditions were observed
to deteriorate during periods of heavy rain showers and the air
traffic control tower staff updated each crew as appropriate.
As the Shorts intercepted the final approach path at 14 NM from
touchdown, the aerodrome controller informed the approach
controller that the weather had deteriorated at the aerodrome and
that there was a likelihood that the Shorts would carry out a
missed approach. The approach controller informed the crew and
transferred them to the tower frequency so that the aerodrome
controller could provide timely updates of the changing weather
situation.
At 0744:05 Eastern Standard Time, the pilot of a Cessna 208
(Cessna) reported ready to depart on the aerodrome control
frequency and was instructed to line-up. At that time, the Shorts
was approximately 9 NM from touchdown with a ground speed of 120
kts.
The aerodrome controller received a departure instruction of
"Left 360 unrestricted" from the approach controller (who was also
providing the departure service). The pilot of the Cessna was then
given a take-off clearance in accordance with that instruction but
with an additional instruction to remain on the aerodrome
controller's frequency when airborne. The aircraft commenced take
off roll at approximately 0745:00; when the Shorts was
approximately 7.5 NM from the runway 15 threshold.
At 0745:05, the crew of the Shorts was informed that the rain
was increasing at the field and that the runway lights were on
stage 6; the maximum intensity.
At 0746:04, the pilot of the Cessna was asked to expedite his
climb through 2,000 ft and, at 0746:30, the crew of the Shorts was
cleared to land.
At 0748:29, the pilot of the C208 apologised for the slow rate
of climb and commented that he was "... just doing his best". At
about the same time, the crew of the Shorts commenced a missed
approach and, at 0748:39, they were instructed to maintain 1,500 ft
and informed that there was "... traffic abeam you now at the 9
o'clock position". That transmission by the aerodrome controller
was followed, at 0748:56, by a broadcast to the pilot of the Cessna
saying "... caution traffic in the missed approach".
At 0749:07, the aerodrome controller updated the traffic
information to the crew of the Shorts with "... caution, the
traffic is in your 12 o'clock position at half a mile". The reply
was garbled and included the statement "... we are maintaining one
thousand at the moment..." which was followed by words that were
not completely discernible but included "... one thousand five
hundred..."
At 0749:27, the pilot of the Cessna was instructed to report
leaving 1,500 ft and replied that he had left that altitude. A
subsequent radar analysis indicated that the aircraft was climbing
through 1,550 ft at that time.
At 0749:40, the approach controller checked with the aerodrome
controller to ascertain his plan for separation. The reply was that
there was "... not much to do". However, at 0749:51, the aerodrome
controller broadcast to the crew of the Shorts that radar indicated
traffic in the same position at the same level. The reply was that
the crew had sighted the Cessna and were passing that aircraft.
Radar analysis indicated that the aircraft had passed at
approximately 0749:50 with a minimum horizontal distance of about
70m and a vertical displacement of between 100 - 200 ft. The
required separation standard was either 3 NM horizontally or
1,000ft vertically. There had been an infringement of separation
standards.
Missed approach and departure procedures
Due to the constraints of terrain surrounding the Cairns
aerodrome, both the missed approach and departure procedures
required tracking in a 40 degree sector to the north east. The
missed approach required an initial climb straight ahead to the
Middle Marker, then a climbing left turn onto a heading of 030
degrees to intercept the 045 radial of the Cairns VOR (Very High
Frequency navigation aid), with a climb to 4,000 ft or a level
assigned by air traffic control.
The standard instrument departure required a left turn at the
earlier of 400 ft or the departure end of the runway, onto an
assigned heading between 350 - 030 degrees. The lowest altitude for
radar vectoring in this sector was between 1,000ft and 3,300ft
depending on the precise position of the aircraft at the time.
This combination of tracking requirements resulted in a
guaranteed tracking conflict whenever a missed approach was
commenced when a departing aircraft was within 3NM of the
aerodrome. Furthermore, an infringement of separation standards
would occur whenever a missed approach was carried out in
instrument meteorological conditions without vertical separation
being established.
Separation standards
Air traffic controllers were limited to a minimum altitude of
1,500 ft for terrain clearance in the case of a missed approach. To
establish the vertical separation standard of 1,000 ft (or 500 ft
in an emergency), a departing aircraft would have to be at or above
2,500 ft (or 2,000 ft in an emergency). When the Shorts was
established in the missed approach turn, it was climbing through
700 ft while the Cessna had left 1,300 ft.
The radar standard was not achieved as the tracks crossed each
other approximately 2NM north east of the runway. As the aircraft
had to track in the same narrow sector of airspace, it would have
been some minutes before a radar standard could be established.
Visual separation was not an option due to the prevailing
weather conditions. The aerodrome controller could not see either
aircraft as they came into conflict.
Lateral separation - the Manual of Air Traffic Services section
6-4-3 stated "lateral separation is considered to exist between an
arriving aircraft that subsequently commenced final approach, and a
departing aircraft that has been cleared on a segregated flight
path". That is, a situation where the departing aircraft will not
be manoeuvring within 45 degrees of the reciprocal of the final
approach path while an aircraft is on the final approach path. The
assigned heading of 360 degrees for the Cessna did not comply with
that standard.
Longitudinal separation standards did not apply because they
required distances greater than those required for radar
standards.
Aircraft performance
The Shorts, a 36 passenger aircraft, had seven persons on board
and very little freight. Consequently, when the missed approach was
commenced, the crew attained a rate of climb of 700 - 800 ft/min.
They stated that 300 - 600 ft/min was their expected rate of
climb.
The Cessna was at maximum take-off weight and, because of the
heavy rain, the pilot had selected the Inertial Separation Handle
to bypass mode. That operation helped to divert heavy rain droplets
around the engine so that the risk of flame-out was reduced.
When airborne, the pilot of the Cessna experienced severe
turbulence and downdrafts, along with buffeting from the gusty wind
and heavy rain. The combination of the prevailing weather
conditions and the selection of bypass mode resulted in a degraded
climb performance from that normally expected. Radar analysis
indicated that the Cessna had an average rate of climb of 400
ft/min from take-off to the point of closest proximity and, at
times, a rate of climb near zero. The pilot stated that he expected
a rate of climb between 800 - 1,200 ft/min.
Air traffic control procedures
The Manual of Air Traffic Services (MATS) section 6-4-3
specified the procedures to be applied in the case of an arriving
aircraft and an aircraft taking-off. It stated that "a departing
aircraft may be permitted to take off during the period before an
arriving aircraft will commence its final approach" but goes on to
say that such take-off clearance "... is conditional upon the
application of separation after take-off is commenced".
Final approach was defined as 8NM from the runway 15 threshold.
The aerodrome controller may have complied with the distance
requirement as the Cessna was cleared for take-off when the Shorts
was approximately 8NM from the threshold.
Cairns Local Instructions (TWR - 29) reinforced the provisions
of MATS in the specific instance of the conflicting missed approach
and departure headings from runway 15. They stated that "...
consideration must be given to increase the cut-off distance used
between the landing aircraft and the aircraft commencing take-off
when weather conditions are such that visual or radar separation of
the overshooting aircraft and departing aircraft cannot occur".
Local Instructions did not specify clearly who had the
responsibility for separating the missed approach from the
departing aircraft. Approach control was responsible for the
airspace but the aerodrome controller had to advise the approach
controller of the most appropriate heading consistent with the
ability to provide separation with other airborne traffic.
Cairns controllers operated in such a way that the aerodrome
controller separated an aircraft on the missed approach path with
other traffic, using visual separation until an alternative
standard could be achieved. As the weather conditions precluded
such an option, a specific alternative was required. Tower
controllers were not rated to provide radar separation and could
only use the radar display "for information". However, Local
Instructions specified that it was the aerodrome controller's
responsibility to ensure that radar separation existed between an
aircraft on short final and not yet in sight and an aircraft
becoming airborne.
MATS 6-5-1 allowed a tower controller to provide an
uncoordinated radar vector to initiate separation in cases such as
a missed approach. However, MATS required Local Instructions to
specify the details. Cairns Local Instructions did not specify any
such details.
Aerodrome controller
The controller had considered extending the cut-off distance but
believed that, as the Shorts had not commenced final approach, he
could safely clear the Cessna for take-off. He had witnessed
numerous departures by Cessna 208 type aircraft and had an
expectancy that the aircraft would climb at a rate which would
enable vertical separation to be easily achieved if the Shorts
commenced a missed approach. He also expected the Cessna to proceed
at a speed that would position that aircraft well ahead of the
Shorts at the crossing point of the departure track and the missed
approach path.
Although the approach controller had nominal responsibility for
the airspace, the aerodrome controller had assumed separation
responsibility when he retained the pilot of the Cessna on his
radio frequency for departure. As the Cessna departed, the
controller observed that it did not turn in accordance with the
standard instrument departure instructions but continued for
approximately half a mile before commencing the turn. He then
noticed that the rate of climb was not as good as he had expected
and, at 0746:11, asked the pilot to expedite through 2,000 ft and
report leaving 2,000 ft. That instruction was to maintain his
traffic management plan of achieving vertical separation with any
missed approach procedure and would have provided a 500 ft
emergency standard if he maintained the Shorts at 1,500 ft in the
missed approach.
As the aircraft closed to within 1.5 NM, the controller gave
traffic information to both crews. However that information did not
include the aircraft type, or height, or relative height. The
information was only position and distance to the crew of the
Shorts and included the words "... traffic abeam you now at the 9
o'clock position". That information was incorrect as the Shorts was
in a left turn and the traffic was actually in the 12 o'clock
position moving towards the 2 o'clock position. The pilot of the
Cessna was advised "Caution, traffic on the missed approach". The
controller asked the other controllers in the tower at the time for
advice but they were unable, in the time available, to offer an
alternative course of action.
When the crew of the Shorts made a broadcast that they were "...
maintaining 1,000 (feet) at the moment..." in the middle of a
transmission that was broken and partly unintelligible, the
controller neither questioned the crew as to their mention of the
words "... one thousand five hundred..." during that broadcast nor
did he issue an altitude instruction. However, he did obtain an
altitude report from the pilot of the Cessna which indicated that
the aircraft had left 1,500 ft on climb. The controller's
subsequent conversation with the approach controller indicated that
he was satisfied with the separation standard saying "...(the
Shorts) supposed to be maintaining 1,000 (ft) the other has left
1,500 (ft) ...".
The controller was of the opinion that the altitude read outs
from the Shorts were varying so much that he did not know that the
aircraft had not maintained 1,000 ft. Radar analysis of the
readouts indicated a relatively steady increase in height over the
90 seconds from 0748:30 - 0750:00 but with two "spikes" at
approximately 1,100 ft (at approximately time 0749:07) and 1,500 ft
(at approximately time 0749:45).
Approach controller
The approach controller had issued the departure instruction for
the Cessna believing that, as the Shorts was about 8NM from
touchdown, the aerodrome controller would not depart that aircraft
until after the arrival, or that the Shorts was in sight and
reasonably assured of a landing. However, the terminology used by
the aerodrome controller "next CYC" indicated that the Cessna would
commence take off within 1 minute of the receipt of a departure
instruction.
As the situation developed, the controller monitored the radio
frequency of the aerodrome controller to observe the plan for
separation. He had heard the requirement to remain with the tower
given to the pilot of the Cessna and considered that the aerodrome
controller had accepted the responsibility for separation with this
action. As the radar display indicated that the aircraft were on
conflicting tracks and at similar altitudes, other controllers
asked what separation was being applied. The approach controller
replied that the aerodrome controller was providing the separation
but elected to prompt the tower with the question "you right?".
This coordination occurred at 0749:40, approximately 10 seconds
before the point of closest proximity, and was the first contact
between the controllers since the departure instruction for the
Cessna was issued.
Emergency training
The Cairns air traffic controllers had not received regular
training in emergency or unusual situations. Tower controllers had
last undertaken formal refresher training in October 1997. However,
the aerodrome controller had been absent on recreational leave and
did not attend the training. He had received formal tuition in
dealing with similar circumstances during his aerodrome control
training in December 1997 and January 1998.
The aerodrome controller stated that he had experienced only one
missed approach due to poor weather in his 3 years at Cairns. As
the incident developed, he asked for advice from his fellow tower
controllers but as they were occupied with their own tasks, they
were unable to give a properly considered response.
Pilot of the Cessna
The pilot was conducting a single pilot operation and had
intended to comply with the requirements of the standard instrument
departure by turning left at 400 ft or the departure end of the
runway. However, when airborne, the initial climb did not proceed
as well as expected, with severe turbulence and heavy rain
buffeting the aircraft. The airspeed was not increasing as quickly
as he would have liked and at the upwind end of the runway the
aircraft had only reached an altitude of 200 - 250 ft. Consequently
the pilot elected to continue on runway heading until a more stable
climb was achieved. The left turn was commenced at an altitude of
300 ft and an indicated airspeed of approximately 70 kts. There was
no broadcast to air traffic control indicating the variation to the
standard procedure.
Once the aircraft had turned onto the assigned heading of 360
degrees, the pilot made every effort to maximise the rate of climb
but was limited by the aircraft performance in turbulent weather
conditions. At 0748:29, he broadcast to the aerodrome controller
that he was experiencing a slower than normal rate of climb.
When, at 0748:56, he was given conflicting traffic information,
he attempted to sight the other aircraft but found visibility
limited in cloud and heavy rain. Shortly after, the aircraft broke
into a small clear patch and the pilot saw the Shorts just below
and marginally to his left. He estimated that the aircraft would
pass just behind his own and elected not to take any evasive
action.
Crew of the Shorts
The co-pilot was the flying pilot and, as the aircraft
approached the minima, the crew found themselves in cloud, heavy
rain and subjected to severe turbulence culminating in their
decision to commence a missed approach.
The crew's main preoccupation was to ensure the safe climb-out
of their aircraft in the left turn required by the procedure and,
as they were experiencing instrument meteorological conditions,
their first priority was to fly the aircraft. Consequently, they
did not immediately inform air traffic control of their commencing
a missed approach. Before they could broadcast any details, the
aerodrome controller issued an instruction for them to maintain
1,500 ft and passed traffic information. As they were still in
cloud and rain, their lookout was both occasional and of limited
effect.
A short time later, the controller issued an updated traffic
alert indicating that the other aircraft was half a mile ahead. The
response from the pilot in command was that they were maintaining
1,000 ft temporarily but still climbing to 1,500 ft as cleared by
air traffic control. The pilot in command had intended to maintain
1,000 ft after the traffic information had been passed but the
co-pilot did not hear the instruction as it was said during the
radio broadcast to air traffic control and during a period of
intense flying activity. As the pilot in command was about to
reiterate the maintain 1,000 ft instruction to the co-pilot, the
aircraft broke into the same clear patch as the Cessna and they saw
that aircraft ahead and slightly above. The co-pilot levelled the
aircraft momentarily to ensure that they would pass beneath the
Cessna and then continued the climb to 1,500 ft when established
clear of it.