Airbus Industrie A320-211, VH-HYO, Adelaide, Aero. SA, 20 August 1999

As the aircraft approached runway 23 for landing, the crew
observed a bank of fog drifting toward the aerodrome from the
north-east. By the time the aircraft arrived at the aerodrome, the
runway threshold was obscured by the fog. As a result, the crew
elected to conduct a missed approach.

During the missed approach, the crew noticed that the threshold
area of runway 05 was clear, so they requested an immediate visual
approach to runway 05 before the fog drifted further to the
south-west. Due to other instrument flight rules traffic, Air
Traffic Control (ATC) could not issue an immediate clearance for
the approach. By the time that clearance was available, the
remainder of the runway was obscured by fog. A B737 aircraft had
been able to land on runway 05 following a VOR/DME approach, so the
A320 crew attempted to conduct a similar approach. However, that
attempt resulted in a second missed approach. The aircraft tracked
to the north-east of the aerodrome and the crew informed ATC that
they would conduct an instrument landing system (ILS) approach to
runway 23, and then land using the aircraft's autoland system. With
1,500 kg of fuel remaining, the aircraft landed without incident in
the fog. Visibility was 250 to 350 m.

The aircraft was certificated for autoland approaches, but the
ground equipment was not. The ILS transmitter was a Category 1 unit
with a minimum visibility of 1,200 m required for landing. The crew
decided to conduct an autopilot-coupled approach with automatic
landing, as fog was also present at the Royal Australian Air Force
base at Edinburgh, rendering that aerodrome unsuitable as an
alternate. The crew considered that Whyalla, the nearest suitable
aerodrome, was likely to have similar weather conditions to
Adelaide.

Fog had not been forecast for Adelaide when the crew submitted
their flight plan. Consequently, the aircraft did not carry fuel
for holding at Adelaide or for diversion to an alternate.

However, fog had been forecast for both Edinburgh and Parafield.
The Bureau of Meteorology (BoM) reported that this was not unusual,
as records showed that in the past 20 years, fogs formed at both
Adelaide and Edinburgh on about 50% of occasions, with Edinburgh
proving to be the greater risk. On the day of the occurrence,
moisture levels were higher to the north of Adelaide, with fog
forming at Edinburgh at 0700 Central Standard Time. What was
unusual about this event was that the advection of fog from the
north took place at a greater speed than the surface wind and that
the onset time of fog at Adelaide Airport was 40 minutes later than
any recorded onset time at that location in the past 30 years.

BoM records showed that Adelaide Airport averaged 4.9 fog events
per annum. The highest annual total for events was nine, recorded
in both 1956 and 1983. At the time of the incident on 20 August,
there had been 11 fog events recorded at Adelaide Airport during
1999.