Fairchild Industries Inc SA227-DC, VH-WAI

The crew of a Metro 23 was cleared by the surface movement
controller (SMC) at Perth to enter runway 11 and taxi to the
threshold of runway 21 prior to departure. However, as the aircraft
approached the runway 11 holding point, the crew checked the final
approach path and saw a Cessna C402 landing on runway 11 in front
of them.

A subsequent investigation revealed that the SMC had previously
been using runway 11/29 as a taxiway for vehicle and aircraft
movements. The procedure for release of the runway from the
aerodrome controller (ADC) to the SMC was for both the ADC and SMC
to de-select their respective runway 11/29 selection buttons. Both
buttons would became illuminated when selected on, indicating that
the runway was active. De-selecting each button had the reverse
effect. Should the button be selected or de-selected on one side
only, both lights would flash to alert the controllers to a
mismatch.

In addition to the use of the runway selection buttons, both
controllers were to coordinate off-line with each other using the
phrase "runway 11/29 released to you" or "runway 11 active" as
appropriate. Any traffic that might be on the runway would also be
coordinated. Those procedures were detailed in the Perth Tower
Local Instructions.

Just prior to the incident, the SMC had control authority for
runway 11/29, and the runway 11/29 selector buttons were in the
de-selected position. When the crew of the Metro requested a taxi
clearance, the SMC cleared them to taxi to runway 21, entering
runway 11 at taxiway Echo. The threshold of runway 21 is at the
midway point of runway 11/29 and access to the threshold of runway
21 was achieved by taxiing via runway 11. Once details of the Metro
were no longer required by the SMC, the flight progress strip for
the aircraft was placed into the top transfer slot on the ADC's
side of the console. This procedure was also documented in Perth
Tower Local Instructions.

Three minutes after the taxi clearance was issued, the ADC
elected to land a C402 on runway 11. Prior to issuing the landing
clearance, the ADC selected the runway 11/29 selector button to
indicate to the SMC that the ADC was taking control authority for
runway 11/29. Because the SMC no longer held a flight progress
strip as a memory marker, he also turned on his selector button and
advised the ADC "no traffic runway 11". The ADC did not notice the
Metro, which had not yet entered taxiway Echo, nor did he notice
the flight progress strip in the top transfer slot. The ADC
subsequently cleared the C402 to land on runway 11.