Virgin Australia B738 at Mildura on Jun 18th 2013, landed below weather minima and substantially below final fuel reserve
Last Update: May 31, 2016 / 13:13:12 GMT/Zulu time
- 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 aerodrome 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.
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 aerodrome weather reports at Mildura over the aerodrome 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 in-flight 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 in-flight weather report given by the air ambulance pilot was not passed 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 recognise and actively disseminate special weather reports (SPECI) to pilots, thus not meeting the intent of the SPECI alerting function provided by controller-initiated flight information service. [Safety issue]
- 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 weather conditions at such airports, increasing the risk of flight crew not being aware of the changes at an appropriate time to support their decision making. [Safety issue] (Editorial note: Emphasis added by ATSB)
- The flight crews of Velocity 1384 and Qantas 735 planned for, and uploaded, sufficient fuel for the forecast conditions at Adelaide Airport in accordance with the respective operator's fuel policies.
- The flight crew of Qantas 735 proactively sought weather information for various airports soon after departing Sydney.
- The meteorological information obtained from an Aerodrome Weather Information Service (AWIS) is operationally equivalent to that provided in routine (METAR)/special weather (SPECI) reports. However, as the AWIS broadcast doesn't contain the label 'SPECI', pilots are required to recognise and interpret its operational significance.
- Critical to the assurance of safe flight, all elements of the aviation system including weather services, air traffic services, aircraft operators and flight crews need to have a clear understanding of their roles and responsibilities in that system.
The ATSB analysed:
After realising that the fog at their original destination of Adelaide Airport would not clear prior to their arrival time, the flight crews of Velocity 1384 and Qantas 735 initiated a diversion to Mildura Airport, Victoria. The diversion was based, in part, on weather observation reports at Mildura indicating the weather was better than forecast. However, on arriving at Mildura, the crew of both aircraft encountered weather conditions worse than those forecast and reported prior to the diversion.
As a result, the crews were compelled to land at Mildura in conditions below the minima permitted for landing, with Velocity 1384 also landing below their required fuel reserves.
The ATSB analysed the weather conditions at Adelaide:
At the time of departure for both aircraft, the forecast conditions at Adelaide Airport were such that an alternate airport was not required. As a result, neither crew was required to carry additional fuel to that calculated for the flight to Adelaide, which included the mandatory fuel reserves. The Virgin Australia Pty. Ltd. (Virgin) and Qantas Airways Ltd. (Qantas) fuel policies were approved by the Civil Aviation Safety Authority (CASA) and each flight crew uploaded sufficient fuel in accordance with their respective policies.
While Velocity 1384 was en route to Adelaide, and while Qantas 735 was in the process of departing for Adelaide, an updated forecast was issued at 0700 including a 30 per cent probability of fog. Within the hour, the weather conditions deteriorated below the landing minima at Adelaide Airport due to fog. This fog was included on the Adelaide Airport trend forecast (TTF) that was issued at 0800 but was forecast to clear by 0900. The crews of Velocity 1384 and Qantas 735 each estimated arriving at Adelaide Airport after 0900.
As the aircraft neared Adelaide, the BoM issued another TTF at 0900. This TTF forecast that the fog would now remain until 0930. Based on this revised information, the crew of Qantas 735 decided to divert to Mildura Airport, rather than holding or conducting an autoland at Adelaide. This decision took into account the observations at Mildura, which indicated the weather there was suitable for landing. The crew of Velocity 1384 (who were not authorised to conduct an autoland at Adelaide as Virgin did not have the appropriate approval from CASA to conduct an autoland) also used the observations at Mildura as the basis of their decision to divert to that airport.
The diversion of two 737 aircraft to an alternate airport due to inclement weather at the intended destination did not result in increased monitoring by ATC. Airservices Australia (Airservices) advised that a diversion in these circumstances would not generally trigger controllers or supervisors to increase their monitoring of conditions at the alternate. Additionally, in this occurrence, the observations showed the weather at Mildura was better than forecast at the time the diversion was initiated.
The BoM reported that the fog conditions at Adelaide were particularly unusual and that, based on their experience, they did not initially expect it to form. In addition, the forecaster believed that once formed, the fog would dissipate fairly rapidly. This explains the fog’s predicted clearance on the TTF of 1 hour after its formation. Given the time of day and expected temperature increase, this was a reasonable assessment. However, on the day the fog did not clear as anticipated, which resulted in the forecast end period for the fog being inaccurate. In addition, the Adelaide aerodrome forecast (TAF) valid at the time retained a 30 per cent probability that visibility would reduce in fog.
The predicted clearance of the fog at 0900 on the 0800 TTF was used by the crew of Qantas 735 to inform their decision to continue to Adelaide from the point at which they could have returned to Sydney. This predicted clearing time was also used by the flight following personnel at Virgin to inform their decision not to pass the 0800 TTF to the crew of Velocity 1384. This was on the basis that, given their arrival time, it would not affect the flight.
The ATSB analysed the weather conditions at Mildura:
The 0158 amended TAF for Mildura Airport was available to both flight crew and predicted a temporary deterioration (TEMPO) of the weather. This included broken cloud at 600 ft above ground level (AGL), which was below the alternate minima for Mildura. This TEMPO meant that anyone flying to Mildura Airport required either 60 minutes of holding fuel to outlast the predicted deterioration, or needed to nominate an alternate destination airport.
The BoM reported that their assessment of Mildura Airport at around 0830 showed that low cloud was more likely than fog, and that improved conditions could be expected from 1000. As the wind was forecast to tend southerly, and fog and low cloud were rare in a southerly flow at Mildura, the decision was made to continue with the current TEMPO.
At around 0900, weather instrumentation at Mildura Airport started to indicate patches of low cloud around 400 ft AGL and a visual satellite image indicated a bank of low cloud south of the airport. The forecast TEMPO was still considered by BoM to be appropriate for the conditions; however, at around 0930, the visibility at Mildura abruptly decreased.
The BoM observer at Mildura Airport advised the forecasting office that the mist and subsequent fog arrived from the south and resulted in a rapid deterioration in conditions. Given the speed at which it developed, the fog was forecast to lift in about 1–2 hours. The forecaster then issued an amended TAF at 0952 with a 30 per cent probability of fog, visibility 500 m and broken cloud at 200 ft AGL for 2 hours. By this time, Qantas 735 had landed at Mildura and Velocity 1384 was holding after advising ATC that they intended to delay their approach to land.
After issuing the 0952 amended TAF, the BoM received a call about the weather at Mildura from the BoM meteorologist located at the Airservices national operations centre. The BoM reported advising that the weather deterioration was unlikely to improve in the next 15 minutes. Velocity 1384 landed at Mildura at 1014, in fog conditions. BoM reported that the fog was observed for approximately 20 minutes after the amended TAF was issued, with low cloud remaining for 45 minutes after the fog cleared. This supports the assessment that the fog would clear rapidly at Mildura.
As previously stated, given the forecast conditions at Adelaide Airport, the flight crews of Velocity 1384 and Qantas 735 were not required to carry fuel for an alternate. However, this reduced their options after the unexpected need to divert from Adelaide to a suitable alternate destination. Their arrival at Mildura Airport in the now deteriorated weather meant that they had insufficient fuel to divert to another airport. As such, both aircraft were committed to land in conditions below the landing minima at Mildura Airport. This contingency in the case of an emergency was permitted under Civil Aviation Regulation 257(5).
The crews’ decisions to hold or attempt an immediate landing at a lower minima at Mildura Airport relied on crew judgement. Given the uncertainty about the duration and trend of the weather deterioration, the decision of the crew of Velocity 1384 to hold and of the crew of Qantas 735 to attempt a landing were both reasonable. While conditions deteriorated after Qantas 735 landed, in different circumstances, the weather may equally have improved sufficiently to allow Velocity 1384 to hold, before landing in conditions above the minima.
With respect to the weather situation awareness of Virgin flight 1384 the ATSB analysed:
When Velocity 1384 departed Brisbane for Adelaide, the TAF that was current at the time showed favourable conditions for arrival and did not require the nomination of an alternate airport. The observations for Adelaide at that time supported that forecast. At the time the amended TAF was issued at 0700, Velocity 1384 was at FL 400 in the cruise, about 150 NM (278 km) from Brisbane.
Flight watch personnel at Virgin reported reviewing this TAF for applicability to Velocity 1384. The review determined that, because the TAF had only a 30 per cent chance of fog and the TTF issued at the same time forecast no deterioration, the amended TAF would not be passed to the flight crew.
At 0800, when the TTF was issued for Adelaide showing fog that was predicted to clear from 0900, Virgin’s flight watch personnel again reviewed the product for applicability to Velocity 1384.
At this stage, the company meteorologist called the BoM to determine their confidence in this clearance and also reviewed other information sources to determine the possible impact of fog on the arrival of Velocity 1384. During the telephone call with the company meteorologist, the BoM supported the content of the 0800 TTF that the fog would clear at 0900. On this basis, the decision was made that, given Velocity 1384 was planned to arrive at Adelaide at 0920, they would not be affected by the fog. As such, the TTF was not passed to the flight crew. In support of this decision, the flight following personnel understood that as this flight was not being actively flight followed, the flight crew would, as part of their normal responsibilities, be actioning any weather updates. In addition, the assessment of the TTF was completed amongst the flight following personnel’s other priorities and workload. As such, the action to not pass this information to Velocity 1384 was provided for by the Virgin dispatch manual. The FO of Velocity 1384 confirmed that this was consistent with their understanding of the Virgin flight following service for domestic operations. That was, the FO was not expecting to necessarily be sent amended weather by flight following personnel. While the 0700 amended TAF and 0800 TTF were not required to be sent to the crew under Virgin’s flight following procedures, not passing the weather removed an important source of information regarding the deteriorating conditions at Adelaide. However, as the deterioration was forecast to improve prior to their arrival, it is likely that, at that stage, they would have elected to continue to Adelaide.
Despite not being passed the updated weather information from their flight operations centre, the crew of Velocity 1384 had two opportunities to become aware of the deterioration in Adelaide prior to being notified at 0844 by the Tailem Bend controller. The first was at 0816 when Qantas 735 queried the conditions in Adelaide based on the forecast of fog in the 0800 TTF. This query was made on the same frequency as was being monitored by Velocity 1384 at the time. However, this call occurred just prior to the commencement of the 2-hour, continuous loop cockpit voice recording for the flight. This precluded a full understanding of what factors may have contributed to the crew of Velocity 1384 missing this report.
The second opportunity was at 0839 when Qantas 735 was updated on the conditions at Adelaide Airport and was told the visibility was now 500 m in fog, with no landing attempts having been made for a while. Another Virgin aircraft then asked ATC to clarify if that report was for Melbourne, to which ATC responded ‘negative, Adelaide’. The FO of Velocity 1384 was absent from the flight deck and the captain reported preparing for the approach into Adelaide at that time. The captain reported hearing this information but did not pass it to the FO on their return. Virgin advised that a review of their operations identified no systemic issue in relation to flight crew seeking weather information. The actions of the flight crew of the second Virgin aircraft to query ATC about the weather update for Adelaide were consistent with this advice.
As the crew of Velocity 1384 did not obtain the updated weather for Adelaide Airport while en route, they remained unaware of the deterioration until quite close to Adelaide. This limited their options and the time available to plan a diversion to a suitable alternate airport. The Virgin operations manual included a requirement for crew to check there was sufficient fuel remaining on board to continue to the destination at the point of no return. This included taking account of the traffic and weather conditions expected at the destination, along the diversion route and at the alternate (if applicable).
Despite the fact that the crew of Velocity 1384 did not seek the weather information for Adelaide Airport, it is probable that had they become aware of the fog on the 0800 Adelaide TTF and its forecast clearance from 0900, they would have elected to continue to Adelaide. Given the actions of the Qantas 735 crew (who did obtain the weather) to continue to Adelaide, this decision would have been reasonable. However, by not obtaining the weather for Adelaide while en route, the crew removed an information source that could have resulted in a better awareness of the situation at Adelaide and the opportunity to plan a diversion earlier.
In situations where crew are primed to search for information, it is more likely that considered decision making will occur in a less stressful environment and that the associated workload will reduce. Conversely, if crew are not aware, or primed, of a situation they may not recognise relevant information that could assist their decision making.
With respect to the weather situation awareness of Qantas Flight 735 the ATSB analysed:
As the flight crew of Qantas 735 was preparing to depart Sydney, just prior to leaving the gate, the 0700 amended TAF for Adelaide was issued. Given the TAF only had a 30 per cent probability of fog, and as the aircraft was in the ‘sterile cockpit’ phase of flight, flight watch did not pass the TAF to the crew at this point. After the aircraft reached top of climb and the sterile cockpit period ended, flight watch sent a message via the aircraft communications addressing and reporting system stating that the amended TAF now indicated a 30 per cent chance of fog, providing an overview of the conditions at Adelaide Airport and advising that the TTF forecast no significant change during its validity period.
Prior to this point, about 5 minutes after take-off, the crew of Qantas 735 sent a request via the aircraft communications addressing and reporting system for the current Aerodrome Terminal Information Service at Adelaide Airport. They then continued to collect weather updates for various ports, including Mildura, Melbourne, Canberra, Sydney and Adelaide. These included updates of forecasts and observations and occurred frequently for the remainder of the flight to waypoint BLACK (48 NM or 89 km from Adelaide).
At 0816 the flight crew received information about the current conditions at Adelaide. This included the 0800 TTF, which indicated the fog would dissipate by 0900. At 0820, Qantas 735 reached their latest point of safe diversion back to Sydney. Information gathered by the flight crew about the conditions at Adelaide from multiple sources continued to show a forecast improvement from 0900. As their arrival time was 0917, the crew elected to continue to Adelaide at this point. Supporting this decision, the flight crew had also calculated that they had sufficient fuel to hold for about 45 minutes beyond their planned arrival time without using the fixed fuel reserve. They considered this was a sufficient buffer if the fog did not clear by 0900.
A number of safety actions were taken by Airservices Australia, BoM and Virgin Australia.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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