The Airbus A320 (A320) departed Sydney for Coolangatta carrying sufficient fuel for the planned flight. In addition to the flight fuel, there was provision for a 10 per cent variable reserve, 60 minutes fixed reserve, 30 minutes holding fuel, plus 200 kg for contingencies. The Coolangatta terminal area forecast (TAF) indicated intermittent (INTER) periods of visibility reducing to 3,000 m in heavy showers. The term INTER is used to indicate a change in prevailing conditions expected to occur frequently for periods of less than 30 minutes duration, the conditions fluctuating almost constantly, between the times specified in the forecast. The Brisbane TAF was similar, with no indication of thunderstorms at either location.
Near Williamtown, en route to Coolangatta, the crew received an "Airport Warning" for Brisbane. An Airport Warning is issued by the Bureau of Meteorology (BoM) to advise airport users of approaching severe weather conditions; it is not a forecast intended for flight-planning purposes by flight crews. The warning indicated that a line of thunderstorms was approaching from the west towards Brisbane, and the crew noted that the Brisbane weather was expected to deteriorate coincident with their arrival at Coolangatta. However, the TAF was not updated until an hour after the BoM became aware of approaching thunderstorms, and the amended TAF was never passed to the crew.
The crew calculated that should a missed approach become necessary at Coolangatta a diversion to Tamworth could be carried out. Tamworth is listed as an "adequate airport for twin engine operations" in the operator's A320 operating manual This listing is relevant to extended range twin-engine operations. Notes appended to the listing indicate that the list is a guide, and that the suitability of the airport should be checked prior to its use. The fuel required to divert was based on a fixed reserve of 30 minutes.
The crew contacted Coolangatta Approach then Coolangatta Tower prior to commencing a descent, and were advised that the weather conditions would be suitable for an approach and landing, but that thunderstorms were approaching from the west. A decision was then made by the pilot in command to continue to Coolangatta, but divert to Tamworth if necessary. Constant updates on the weather at Coolangatta were passed to the crew during the descent, and aircraft radar returns indicated a clear approach path with storms cells still to the west of Coolangatta. Advice was received by the crew that Brisbane weather was deteriorating rapidly at this time, with rain and lightning close to the airport.
A runway 32 VOR/DME approach was commenced to Coolangatta and the crew became visual at approximately 1,500 ft. The approach proceeded normally, with the full length of the runway being visible in light to moderate rain. The co-pilot was the handling pilot, and the pilot in command considered the weather conditions exceeded company requirements for a co-pilot approach and landing. However, at about 800 ft, the co-pilot unexpectedly commenced a missed approach, commenting that he did not like the conditions. Due to the rapidly deteriorating weather the pilot in command decided there was no option but to carry out the diversion to Tamworth.
The crew was subsequently advised by company central operations to divert to Williamtown rather than Tamworth as the company did not have a standing pavement concession for the use of Tamworth, and the airport was not included in the company's air operator certificate. As the aircraft would not arrive at Williamtown with the required fuel reserves intact, the crew declared a fuel emergency to air traffic control. The aircraft arrived at Williamtown with fuel equivalent to a fixed reserve of 27 minutes.