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.
Local safety action
As a result of this occurrence, the BoM's analysis and report of the meteorological aspects of the occurrence included the following recommendations:
- As BoM's observation stations at Parafield and Edinburgh will be closed before the winter of 2000, BoM should consider installation of a "Skycam" on a city building to better appreciate the extent of fog and low cloud when the conditions that led to this occurrence are present. In addition, BoM should urgently consider a research project on guidance material for prediction of fog events at Adelaide and Edinburgh airports.
- As BoM's observing site is poorly located at Adelaide Airport in reference to fog and low stratus cloud to the north of the airport, BoM should consider relocation of the site to eliminate this impediment.
- BoM should conduct a workshop for local forecasters on fog events and local guidance before the winter of 2000.
On 16 December 1999, BoM reported:
- BoM was considering "Skycam" installations on a national basis, expecting that trials would be conducted in the eastern states due to higher traffic levels.
- The relocation of the BoM's observation site at Adelaide Airport was included in the airport upgrade. In addition, a radio was installed in the BoM's airport office enabling forecasters to monitor the Automatic Terminal Information Service (ATIS) from Adelaide, Parafield and Edinburgh.
- Research and workshops were an ongoing requirement in BoM, but depend upon staff availability.
On 19 July 2000, BoM reported:
- BoM assessed the range of Skycam units available and obtained the agreement of the aviation industry to fund the installation of one unit at a major airport (not Adelaide). The industry has undertaken to assess the value of the information obtained from that unit before making any decision on possible funding of further units.
- The BoM offices at RAAF Edinburgh and Parafield closed in December 1999. Since those closures, an automatic weather observation station was installed and has been operating at RAAF Edinburgh. The tower controllers at Parafield have also been providing some observations.
- The relocation of the BoM office at Adelaide Airport was scheduled for December 2000, but could be delayed until early 2001. The proposed new site for the office was closer to the runways than the present office and was expected to provide better views of fog areas and low cloud than were available from the present site.
- It has not been possible to hold workshops due to staffing limitations.
|Date:||20 August 1999||Investigation status:||Completed|
|Time:||0830 hours CST|
|Release date:||28 August 2000||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Airbus Industrie|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Melbourne, VIC|