Fairchild Industries Inc SA227-DC, VH-WBA

As a result of this and other occurrences, the Bureau of Air Safety Investigation is investigating a safety deficiency relating to the use of conditional clearances for runway entry and runway crossings by vehicles and aircraft. An assessment of the procedures used by air traffic controllers to alert themselves that vehicles or aircraft are on an active runway is to be included.

Safety output issued as a result of this analysis will be published in the Bureau's Quarterly Safety Deficiency Report.

The aerodrome controller did not change the 'runway designator' strip to indicate that Car 23 had entered the runway.
The aerodrome controller did not adequately scan the runway prior to issuing a landing clearance to the crew of WBA.

The reduced density and complexity of the traffic may have relaxed the aerodrome controller to the degree that he was less alert than required when clearing WBA to land. The use of the 'runway obstructed' strip and the 'runway designator' strip should have assisted the controller to maintain an adequate awareness of the vehicle activity on the airfield. However, at the time of the occurrence, the 'runway designator' strip provided misleading information on the runway obstruction.

Although he scanned the runway prior to clearing WBA to land, the aerodrome controller did not expect to see a vehicle, as he was aware that the tractors were no longer obstructing the runway. Both strips had been in the bay for some time, which could have served to further diminish possible recall that Car 23 was now on the runway. It is also likely that the white colour of Car 23 made it difficult to see against the background of white runway markings or white gable markers. Consequently, without an effective alert to the presence of the vehicle on the runway, the controller's scan was inadequate to see Car 23.

The reason why the aerodrome controller did not follow his normal practice and change the notation on the 'runway designator' strip to indicate that Car 23 was on runway 21 could not be determined.

The crew of a Metroliner, VH-WBA, had flight-planned from
Plutonic Mine in Western Australia to Perth. On first contact with
Perth Tower, the crew were instructed to continue the approach for
sequencing with VH-EAM, which was to land on the crossing runway
24. After EAM had landed and was clear of runway 03/21, the
aerodrome controller noted that his 'runway designator' strip had
'Tractor' written on the runway 03/21 section. He observed the
tractor to be clear, scanned the runway and, when WBA was 5-6 NM
from touchdown, cleared the aircraft to land on runway 21.

At the time the landing clearance was issued, Car 23 was parked
on the runway, approximately 200 m from the southern end. The
surface movement controller reacted by instructing Car 23 to
'vacate 21 immediately'. Using binoculars, the controller observed
the technician throwing tools and equipment into the back of the
vehicle. The controller assessed that Car 23 would not vacate
runway 21 prior to WBA crossing the runway threshold, and advised
the aerodrome controller. The aerodrome controller then directed
that the aircraft go around, advising the crew that a vehicle was
on the runway. The pilot in command estimated that WBA was at about
400-500 ft when they were instructed to go around and both pilots
looked for, but did not sight, the vehicle on the runway.

The surface movement controller was in radio communication with
four vehicles. Car 23, a white vehicle equipped with a flashing
yellow light, had been on and off runway 21, conducting instrument
landing system checks. Tender 1 was being repositioned across the
airfield and two tractors were engaged in mowing near the threshold
of runway 21. Shortly before the incident, both tractors were clear
of the threshold area and Car 23 requested approval to enter the
runway for the fourth time. Once on the runway, Car 23 required a
1-minute recall to allow for the clearing of tools and equipment.
The surface movement controller noted that no aircraft were due
immediately and checked with the aerodrome controller for a
clearance for Car 23 to re-enter runway 21. The aerodrome
controller approved the clearance, but did not change the 'runway
designator' strip notation to indicate that runway 21 was now
obstructed by Car 23. The surface movement controller then cleared
Car 23 to enter the runway.

The procedures in use at the time required that an individual
clearance be obtained each time a vehicle entered or crossed a
runway. As a memory prompt, both the aerodrome controller and the
surface movement controller utilised red flight progress strips
engraved with the words 'runway obstructed'. The aerodrome
controller would place the strip above the 'taxiing aircraft' bay
on the console. In addition, the aerodrome controller used a red
'runway designator' strip which was divided into three sections
indicating the runways 03/21, 06/24 and 11/29.

When a vehicle was cleared onto the runway, the 'runway
designator' strip was moved into the console's 'active runway' bay.
The vehicle's callsign would then be written in the section that
designated the obstructed runway. The annotation of the 'runway
designator' strip with vehicle callsigns was not a requirement of
the Local Instructions, but was a normal practice of the aerodrome
controller.

The use of the flight progress strip was intended to assist the
controller's situational awareness in two ways: (1) the action in
placing the strip in the appropriate console bay (setting the
memory prompt) should have assisted in consolidating a strong
memory trace, and (2) the strip could be checked at any time should
the controller be unsure as to the status of the item or condition
referred to. The use of the 'runway designator' strip with the
vehicle callsign notated provided an additional memory prompt.

Four air traffic controllers were rostered for duty in the
control tower at the time of the incident. In addition to the
aerodrome controller and the surface movement controller, the team
leader was in the Airways Clearance Delivery position and a fourth
controller was performing administrative duties. The Coordinator
position was not occupied because the team leader considered that
the traffic was light. Each controller was appropriately trained
and rated in their operating position. All were extensively
experienced in tower operations at Perth. The controllers had
earlier completed a busy traffic sequence and were in a lull
between sequences at the time of the occurrence.