At the end of a remarkable chain of inaccurate weather forecasts and missed communications opportunities, two Boeing 737-800s operated by different Australian airlines had to bust minimums within minutes of each other at Mildura Airport to prevent really bad outcomes.
It all happened on June 18, 2013. BoeingVH-YIR, operated by Virgin AustraliaAirlines as Velocity Flight 1384, and Boeing VH-VYK, operated by Qantas Airways Ltd. as Qantas Flight 735, were on scheduled passenger flights to Adelaide, South Australia.
The story of what happened to these airplanes, crews and passengers is best told by the investigators of the Australian Transport Safety Bureau (ATSB).
Velocity 1384 departed Brisbane, Queensland, at 0638 Eastern Standard Time (UTC +10) with six crewmembers and 85 passengers on board. The estimated time of arrival at Adelaide was 0920. The captain was the pilot flying and the first officer (FO) was the pilot monitoring. The fuel on board at takeoff from Brisbane was 8,800 kg (19,401 lb.)This comprised flight fuel to Adelaide of 6,410 kg (14,132 lb.), variable and fixed fuel reserves of 1,540 kg (3,395 lb.) and additional fuel of 940 kg (2,072 lb.).
Qantas 735 departed Sydney, New South Wales, at 0727 and had six crew and 146 passengers on board. The estimated arrival time at Adelaide was 0917. The captain was the pilot flying, with the FO as pilot monitoring. The fuel on board at takeoff from Sydney was 7,900 kg (17,416 lb.). This comprised flight fuel to Adelaide of 5,000 kg (11,023 lb.), variable and fixed fuel reserves of 1,600 kg (3,527 lb.) and additional contingency fuel of 1,300 kg (2,866 lb.).
At 0700, the Bureau of Meteorology (BoM) issued an updated airport forecast (TAF) for Adelaide calling for a 30% probability of fog developing. At 0800, the BoM issued an updated trend forecast (TTF) that showed that fog had reduced visibility at Adelaide and was expected to clear by 0900.
At this stage, the crewmembers of Qantas 735 were aware of the changes to the TTF and continued to Adelaide on the basis that the fog would clear prior to their arrival. In addition, they had sufficient fuel to hold for about 45 min. should the fog last longer than forecast and land with required fuel reserves.
The pilots of Velocity 1384 were not aware of the changes to the forecast. They were advised of fog at Adelaide by ATC at 0844, once they changed to the en route sector frequency immediately prior to reaching the Adelaide terminal area airspace.
The crew of Qantas 735 elected to hold at waypoint Black, about 48 nm from Adelaide, rather than continue their descent to the airport, which was still affected by fog.
The crew of Velocity 1384 had commenced their descent to Adelaide and gathered further information about the conditions from the Adelaide tower controller. Based on the report from the Adelaide tower controller that conditions were not suitable for landing, and that there had been no successful landing attempts, the crew of Velocity 1384 elected to divert to Mildura, Victoria, at 0904.
The observation reports issued by the BoM at that time indicated that the conditions at Mildura were above the alternate minima for the aircraft, despite the TAF for Mildura indicating a temporary deterioration during the forecast period. The crew’s estimated arrival time at Mildura was 0932.
The crew of Qantas 735 heard Velocity 1384 broadcast their decision to divert to Mildura. On being informed by ATC that the latest trend forecast for Adelaide predicted a 30-min. delay in the fog clearing, and after gathering observation reports for Mildura, the crew of Qantas 735 also elected to divert there at 0913. Their estimated arrival time at Mildura was 0942.
In making the decision to divert to Mildura, the captain of Qantas 735 reported that they were aware that they had the capability to conduct an autoland at Adelaide Airport. However, based on the reports of significantly better weather at Mildura, a diversion to that airport was assessed as preferable to continuing to Adelaide.
The captain of Velocity 1384 similarly reported that they considered the option of an autoland at Adelaide. However, given the observations of the better weather at Mildura, they also concluded a diversion was a better option at that time.
Arrival at Mildura
At 0916, the pilot of an air ambulance flight departing Mildura made a call to ATC that conditions were deteriorating. He reported the cloud base was at 400 ft. MSL. At the time, neither Velocity 1384 nor Qantas 735 were on this frequency and therefore did not hear this transmission.
At 0918, just after Velocity 1384 transferred to this frequency, the controller for this sector informed them of four other aircraft due to arrive at Mildura around their arrival time. This included Qantas 735. At 0922, Qantas 735 transferred to the same frequency and was advised of the arriving traffic.
Also at 0918, the BoM issued a SPECI (special weather report) for Mildura, showing clouds at 200 ft. AGL but visibility in excess of 10 km (6.2 mi). The Mildura RNAV GNSS instrument approach to Runway 27 required pilots to be clear of cloud at a minimum of 660 ft. (493 ft. AGL), reducing to 560 ft. (393 ft. AGL) using an actual airport QNH (altimeter setting that shows airport ASL elevation when the airplane is on the ground). As the conditions had deteriorated below these minima, the RNAV GNSS approach could not be conducted in normal operations. The airport forecast for Mildura, valid at that time, contained a temporary deterioration with cloud at 600 ft. AGL.
Between 0928 and 0932, three further SPECIs were issued for Mildura, indicating that visibility was decreasing in mist. As the Automatic Weather Information Service (AWIS) for Mildura was out of service, the inbound aircraft could not obtain this information from the AWIS.
At 0936, the controller made a broadcast on the area frequency to traffic at Mildura, informing them of the details of the 0932 SPECI. This SPECI indicated broken cloud at 200 ft. and visibility of 2,100 meters (6,890 ft.) in mist. A review of data from the cockpit voice recorder of Velocity 1384 identified that, for the duration of the controller’s broadcast of the SPECI, the crews of Qantas 735 and Velocity 1384 were busy communicating on the Mildura common traffic advisory frequency.
At 0937, the crew of Qantas 735 contacted the crew of Velocity 1384 to discuss the arrival and the crew of Velocity 1384 stated that they were tracking to the initial waypoint to commence the RNAV GNSS approach to Runway 27.
At 0939, the crew of a QantasLink Bombardier DHC-8 (Dash-8) aircraft broadcast to traffic at Mildura that they were conducting a go around. The crew of Velocity 1384 asked for an assessment of the weather and were told by the Dash-8 crew that at the minima, they “couldn’t see anything.”
At 0940, the crew of Qantas 735 contacted Velocity 1384 to advise that they were commencing the RNAV GNSS approach “due fuel.” The Velocity 1384 FO replied that they were “in the same boat,” but, after discussion between the captain and FO of Velocity 1384, they elected to hold and allow Qantas 735 to continue with the approach. This decision was passed on to the crew of Qantas 735.
The crew of Qantas 735 applied a revised minimum to the approach that was 200 ft. lower than that published. This was based on the knowledge that the cloud base would preclude becoming visual via a normal approach. The crew reported that as they descended toward the revised minimum, the extent of the cloud reduced and they gained sufficient visual reference of the runway environment to continue the approach. At 0946, the crew of Qantas 735 broadcast that they had landed at Mildura. The aircraft landed on Runway 27 with the required fuel reserves intact, and the crew reported that the runway was visible once they descended below the cloud.
At 0948, the crew of the Dash-8 asked Qantas 735 for their assessment of the weather. The crew replied that the cloud base was at 150 ft. AGL and that they had landed off the approach “due fuel.” At this time, a SPECI was issued for Mildura, showing visibility was now 900 meters (2,953 ft.) in fog and that the cloud was overcast at 100 ft. AGL.
At 0950, Velocity 1384 sought an update on the weather from the Qantas 735 crew, who stated that the fog had appeared to be getting thicker but was now clearing, although the cloud was still below minima.
At 0952, Velocity 1384 updated ATC that they were still holding due to the low cloud at Mildura. ATC asked them to nominate a latest divert time to proceed to a suitable airport. The FO replied that they did not have the fuel to proceed anywhere else. After obtaining further information from the crew, ATC initiated an alert phase and at 0958, after contacting the crew again, ATC activated the Mildura Airport emergency procedures.
At 0954, the controller made another “all stations” broadcast with the latest TAF issued for Mildura, valid from 1000. This forecast predicted:
Visibility of 3 km (1.9 mi.) in mist;
Scattered cloud at 300 ft. AGL;
An improvement in both visibility and cloud base in the hour from 1000;
A 30% probability of the visibility reducing to 500 meters (1,640 ft.) in fog for the period between 1000 and 1200.
Given their available fuel, the crew of Velocity 1384 determined that they needed to commence an approach just after 1000 to allow for a second approach if needed. They discussed conducting a “sighting” approach to ensure the aircraft was aligned with the runway from the RNAV GNSS approach. The captain was still the pilot flying; however, they briefed that if at any time during the approach the FO sighted the runway, then the FO was to take control and land.
At 1002, Velocity 1384 transmitted that they were on a 4 nm (7 km) final for the RNAV GNSS approach. At 1004, as they were not visual with the runway, the crew initiated a missed approach from 132 ft. AGL. The FO reported that as they commenced the missed approach, it was possible to confirm that they were aligned with the runway by looking directly down. At 1012, ATC initiated a distress phase.
The aircraft was positioned for a second approach, during which the cabin crew were briefed and prepared for an emergency landing, briefing the passengers to brace accordingly. At 1014, Velocity 1384 landed at Mildura in foggy conditions with fuel below the required reserves. As they taxied in, the captain told the cabin crew to stand down and normal arrival procedures resumed.
The Investigators’ Analysis
Following months of investigation, the ATSB observed that the Australian aviation weather reporting, forecasting and distribution systems are world-class but could use improvement. Company flight watch services at both air carriers are usually reserved for long-haul flights, leaving short-haul flight crews with the responsibility to pursue weather updates on their own once they are dispatched. In this situation, the observations and forecasts were changing quickly and information on Adelaide weather (and later Mildura’s weather) just didn’t form a picture for the crews in time to avoid the below-minimums approaches. The ATSB is suggesting further studies by Australian aviation civil and government agencies to see if improvements can be made.
The Safety Bureau looked at decision-making in each cockpit and ultimately found that the pilots made reasonable decisions including the decision to bust minimums.
ATSB Safety Issues
Ultimately, the ATSB identified a series of “safety issues.” Also, as a result of this investigation, the Safety Bureau initiated a research investigation that will “initially examine the reliability of the airport forecasts for Mildura and Adelaide, before expanding to cover other major Australian airports.” The idea is just to see where the system can be improved.
According to the ATSB, a “safety issue” is an event or condition that increases safety risk and (a) can reasonably be regarded as having the potential to adversely affect the safety of future operations, and (b) is a characteristic of an organization or a system, rather than a characteristic of a specific individual, or characteristic of an operating environment at a specific point in time. Here are the safety issues that arise from this event.
The meteorological conditions at Adelaide Airport deteriorated below the landing minima while Velocity 1384 and Qantas 735 were en route to Adelaide.
The inaccuracy of the forecast clearance of the fog at Adelaide Airport compelled the flight crews of Velocity 1384 and Qantas 735 to either conduct an emergency landing at Adelaide or divert to Mildura Airport.
The actual weather conditions encountered by the flight crews of Velocity 1384 and Qantas 735 on arrival at Mildura were below landing minima and significantly worse than the airport forecast and weather reports used by both flight crews to assess its suitability as an alternate destination to Adelaide.
On arrival at Mildura, Velocity 1384 and Qantas 735 had insufficient fuel to divert to any other airport and were committed to a landing in conditions below their landing minima.
For many non major airports in Australia, flight crews of arriving aircraft can access current weather information using an Automatic Weather Information Service via very high frequency radio, which has range limitations. Where this service is available, air traffic services will generally not alert pilots to significant deteriorations in current conditions.
Other factors that increased risk:
The flight crew of Velocity 1384 did not obtain updated weather information for Adelaide while en route and were therefore unaware of the weather deterioration affecting the airport, limiting the options and time available to plan a diversion to an alternate destination airport.
The flight crews of Velocity 1384 and Qantas 735 gave precedence to the airport weather reports at Mildura over the airport forecast when deciding to divert.
Despite the Bureau of Meteorology (BoM) knowing of the deteriorating weather at Mildura from other sources, by not passing on the inflight weather report of deteriorating weather from the departing air ambulance pilot, the controller removed an important source of information for use by the BoM.
The inflight weather report given by the air ambulance pilot was not passed on to the flight crews of Velocity 1384 and Qantas 735 by the controller when they changed frequency in bound to Mildura Airport, removing an important source of information for flight crew planning and decision-making.
The automatic broadcast services did not have the capacity to recognize and actively disseminate special weather reports (SPECI) to pilots, thus not meeting the intent of the SPECI alerting function provided by the controller-initiated flight information service.
Last Thought
These crews were led into a subtle trap when all tolerances added up unidirectionally, leaving only their exceptional airmanship to save the situation. However, the investigation does make the point well that pilot skills must include a high degree of skepticism when evaluating weather information and forecasts when marginal weather is forecast.