Description

On 22 November 2021, a Fokker F100 (VH-NHV) operated by Network Aviation on a passenger service from Perth to the uncontrolled airport at Paraburdoo on behalf of Qantas Airlines as QF1616 departed with normal fuel reserves and an estimated landing weight close to the maximum permitted on the basis of a destination forecast which did not indicate any deterioration in cloud below 1000 feet. By the time the flight reached its destination, a significant deterioration in cloud base had occurred, After three unsuccessful LNAV approaches, a landing was only achieved by continuing a fourth approach significantly below the applicable MDA.

Investigation

An Investigation into the event was carried out by the Australian Transport Safety Bureau (ATSB). It was noted that the captain had a total of 6,698 hours flying experience, which included 2,641 hours on type. The first officer had a total of 6,735 hours flying experience, which included 1,556 hours on type. Fatigue was not considered by the pilots or the Investigation to have been involved.

What Happened

On boarding the aircraft, the QF1616 flight crew downloaded and reviewed their flight plan for the 90-minute flight to Paraburdo on their EFBs. Relevant FDR and CVR data were available. The Paraburdo TAF (aerodrome forecast) was giving visibility greater than 10km with scattered (SCT) cloud at 1,000 feet AGL and broken (BKN) cloud at 3,000 feet AGL with a TEMPO (temporary) of broken cloud at 1,000 ft and visibility reduced to 4,000 metres. The crew were aware that their preferred alternate, Karratha, was forecast to have better conditions than Paraburdo and that Newman, which was nearer, was forecast to have similar conditions to Paraburdo. The expected traffic load was such that the flight would need to depart with little more than the minimum allowable fuel, but given the forecast data, this was considered acceptable. As departure neared, the crew were notified of a slightly reduced traffic load than had initially been expected which would have allowed the upload of 847 kg more fuel, but as the fuel truck had departed, it was decided that given the expected weather, it was not necessary to delay departure by recalling the fuel truck. 

The flight reached its cruise altitude of FL350 just under half an hour after takeoff with the first officer acting as PF. About an hour after takeoff, the Paraburdoo AWIS was listened to and was giving 050°/6 knots, SCT cloud at the equivalent of 700 feet AGL, BKN cloud at 3,400 feet AGL and OVC (overcast) at 5,300 feet AGL with the surface air and dew point temperatures 20°C and 19°C respectively. With RNP and VOR approach procedures available for both directions of the Paraburdoo runway (06/24), the crew began preparations for an RNP approach to runway 06 based on company-modified LNAV minima. Network Aviation F100s were not approved for use of (lower) LNAV/VNAV minima, and the alternative VOR minima were marginally higher than LNAV ones. 

The applicable LNAV landing minima for runway 06 was the published MDA of 2,010 feet (604 feet AGL) reduced by 100 feet subject to an accurate QNH being obtained within 15 minutes of arrival but the aircraft operator also required that 50 feet be added “for the purposes of commencing a missed approach." For runway 24, the published MDA was 2,090 feet (684 feet AGL) also reduced by 100 feet if an accurate QNH was obtained within 15 minutes of arrival but again the aircraft operator also required that 50 feet be added for the purposes of commencing a missed approach. The crew were therefore required to operate to a minimum of 1,960 feet (554 feet AGL) for runway 06 and to a minimum of 2,040 feet (634 feet AGL) for runway 24. An AWIS was available for provision of METAR and SPECI (Special Weather Report) reports to State Meteorological Service and the State ANSP Airservices Australia. A CTAF was available with ATS provided by a FIR information frequency.

Twenty minutes prior to the flight’s destination ETA, the captain called on the ground radio frequency to advise this and their ground handling requirements and descent clearance was then obtained from Melbourne ACC who were also advised of their ETA. Passing FL240, the captain advised listening to the AWIS again, noting that there was no significant change and that the reported rainfall was “less than moderate." He then selected the Paraburdoo CTAF and turned on the Pilot Activated Lighting (PAL) which provided PAPI indications for the intended non precision approach as well as low intensity runway edge lighting. 

The approach checklist was completed in good time and just after passing the initial approach fix (IAF) the PF decided to configure the aircraft early due to the expected tailwind component on the approach to the 2,132 metre-long runway and then changed the AP vertical mode from ALT Hold to VS and commenced final descent towards the MDA of 1,960 feet. On reaching it, the aircraft was still in cloud and with no visual reference available, a go-around was commenced. Both pilots subsequently stated at interview that they had then seen the runway with the PAPI indicating 4 white lights and were therefore too high to land safely.

During the climb, the crew “concluded that they were too high on the approach due to a tailwind and decided to make a second approach to the opposite runway direction 24 and made a corresponding announcement of their intention on the CTAF". Whilst setting up for this second approach, the captain observed that “the weather at all the surrounding airports” (see the illustration below) was unsuitable and then listened to the AWIS, which was giving cloud BKN at 800 feet aal and OVC at 1,500 ft with visibility 5,000 metres.

The approximate nil wind diversion range from each missed approach at Paraburdoo. [Reproduced from the Official Report]

On completion of the climb and positioning for a runway 24 approach, the PAL was activated and a CTAF call made to announce their intention to conduct the approach. The crew also advised another company flight also inbound to Paraburdo that they had commenced the approach to runway 24. This announcement was followed one minute later by a call from another company flight, reporting that they had landed at Newman.

On reaching the runway 24 company MDA of 2040 feet, the required visual reference was again not available and a go-around was flown. The crew explained at interview that this time, they had made visual contact with the ground on the approach, but low cloud ahead had obscured the runway. The aircraft was climbed to 4,100 feet QNH and during discussion on the weather, they noted that although an aircraft had landed at the nearest potential alternate, “they were uncertain of the actual weather conditions at that location” and had only about 40 minutes of holding fuel left which was, according to the FMC, the minimum required to divert direct to Karratha from their current position. The captain was aware that the FMC calculation for such a diversion assumed still air en route and did not allow for an instrument approach. Because Newman was closer, they considered the possibility of diverting there, which would allow an approach with a fuel reserve. Melbourne ACC were advised of the second missed approach due to low clouds and asked to obtain the latest weather for Newman. It was noted from the CVR data that this request had not been communicated with any urgency or reference to the aircraft fuel status, and the crew then “diverted their attention to their other tasks, which included traffic inbound to Paraburdoo." It was agreed that as there was enough fuel remaining for two further approaches at Paraburdoo and, having decided on this, the other company aircraft inbound there was advised of this intention. Its crew responded that they had “sufficient fuel for 35-40 minutes holding before reaching the minimum fuel for a diversion to Karratha”.

A third approach, this time to runway 06 (MDA 1960 feet), also failed to provide the required visual reference and a go-around was again flown with PF first officer commenting that “the runway 24 approach was better” and the captain noting that “the wind was getting worse." The aircraft was climbed to 5,200 feet QNH and entered a holding pattern to prepare for another RNP approach to runway 24 (MDA 2040 feet). A couple of minutes later, noting that they still had 1800 kg of fuel remaining, it was decided to continue holding a bit longer in order to allow the other company aircraft inbound to Paraburdoo to make an approach to runway 24 first, an offer which was accepted but subsequently unsuccessful. Whilst in the hold, the possibility of a diversion to Solomon which was 55nm to the north was discussed, but after noting that the lowest MDA there was equivalent to 200 feet higher above the runway than at Paraburdoo, this option was discounted in favour of a fourth approach at Paraburdoo. The Paraburdoo AWIS was by now giving BKN cloud at both 400 feet AGL and 800 feet AGL with a visibility of 4,200 metres and a surface wind of 270° at 6 knots. A third company aircraft then broadcast that they were inbound to Paraburdoo, and Melbourne ACC notified them of two other aircraft ahead also aiming to land there.

The captain was recorded remarking that they had “12 minutes of fuel remaining before landing with a 1.1 tonne fuel reserve” and took over as PF. The decision whether to comply with the missed approach criteria and declare a ‘MAYDAY Fuel’ if not visual at the MAPt (which was located at the runway threshold) or ignore them and continue descent below MDA to a landing if not visual at that point was discussed and it was agreed to follow the latter plan. As the crew reached the point where they expected to be able to commence a final approach, Melbourne ACC broadcast a SPECI alert for Paraburdoo. This was followed by a call on the CTAF from the other company aircraft that they had commenced a missed approach and followed by another ACC broadcast to advise a SPECI alert for Solomon.  

The first officer made a CTAF call that they were commencing an approach to runway 24 and the captain “emphasised to the first officer that they both needed to be prepared to call a go-around if either of them sensed the approach was becoming unsafe”. As the approach passed 3nm to go, the EGPWS automatic 1000-foot AGL callout occurred and was followed shortly afterwards by the PM calling 3 nm and “on profile." Ten seconds later, at 844 feet AGL and 273 feet above the 2,040 feet MDA, the first officer was recorded remarking that “the cloud was starting to break”. The MDA was called and descent was continued as automatic callouts of 500 feet, 400 feet and 300 feet AGL occurred before the AP was disconnected as the first officer announced runway in sight at 293 feet AGL - almost 300 feet below the MDA - with a landing following without further event. Following the landing, almost an hour after the first missed approach, the First Officer made a CTAF broadcast advising that “there were some very low patches of cloud at 250-300 feet AGL."

The crew subsequently stated that when they became visual with the runway, they had been slightly left of the extended runway centreline on the PAPI vertical profile. This was consistent with FDR data “which indicated a steady descent profile on the approach and a maximum of 5° heading change between the autopilot disconnect and touchdown”. 

A view of the runway with the aircraft on its landing roll. [Reproduced from the Official Report]

Why It Happened

The Investigation examined the decision not to divert, the eventual landing below minima, and the reason for the unforecast low cloud as well as the delay in ATC weather updates, the limited in-flight access to weather information whilst holding at Paraburdoo, the arrangements for weather forecasting at the airport, and the operator’s procedural guidance and risk management for unforecast weather.

• The decision not to divert 

On the basis of predeparture information the crew had a reasonable expectation that the destination weather should not be an issue, and that if a diversion was necessary for that or any other reason, it would be achievable. However as the destination neared, it became clear that conditions had deteriorated to marginal at best with no evidence that this was necessarily temporary. Decision-making was no longer predicated on preflight information and it was considered that the crew were likely to have lost confidence in the received preflight forecasts. To be sure of reaching their preferred alternate on the basis of readily available information, they would have had to divert after the first approach. However, the Investigation concluded that although the crew had been unsure if a diversion could have been made to Karratha (as well as to Newman) after the second approach, there had actually been sufficient fuel available had they had access to relevant actual weather conditions.  

• The Below Minima landing 

It was only after the second missed approach that the crew began to discuss diversion options and during this time, fuel consumption was quickly precluding a diversion to Karratha as an option. After the third missed approach, a diversion to Solomon was the only other potential option. Although this was ruled out because the lowest landing minima there was higher than at Paraburdoo, it was actually unsuitable anyway with the cloud base below the approach minima. Committed to a fourth approach at Paraburdoo, the briefing included a contingency plan if either pilot judged the approach to have become unsafe and was ultimately achieved only with a significant violation of landing minima, which did not result in such an unsafe situation. 

• Forecast Accuracy

Overnight prior to the investigated flight departure, there were no meteorological observations from the region of persistent low cloud and in addition, the presence of a mid level cloud layer “should have limited overnight surface cooling”. This cloud layer had also obscured the ability to detect any low-level cloud by reference to satellite imagery. The Meteorological Service accepted the proposition that this justified their cloud forecast of SCT at 1,000 feet and TEMPO BKN at 1000 feet at Paraburdo and other aerodromes in the region level, 1000 feet being well above the crew’s LNAV landing minima. This forecast also took into account the expectation that surface heating would lift the cloud base after sunrise but this did not happen. The cloud base at Paraburdo lowered and remained below the highest alternate minima for almost 3½ hours beginning 15 minutes before the first missed approach and deteriorated to BKN cloud at 400 feet AGL prior to the final approach and persisted after the landing. It was considered that this significant failure in forecasting was likely to have led to an expectation by the crew that conditions would at least not deteriorate further after their first missed approach. Whilst the underlying reason for the issue of inaccurate TAFs was the absence of necessary atmospheric data measurements, it was noted that plans to upgrade weather balloon and weather radar stations around Australia do not currently include Paraburdoo Airport and the Investigation “did not identify a trend from the last 10 years of data associated with this airport to warrant (the identification of) a Safety Issue at this stage”.

• In-flight access to weather information

There was a significant lack of access to updated weather reports whilst in flight. The aircraft was not equipped with operational ACAS, so the operator could not supply this directly (and in any case, the datalink required would have only functioned at a minimum altitude of 11,000 feet). Also, reception of the only Automatic En Route Information Service (AERIS) broadcast covering the Paraburdo region required a minimum altitude of around 36,500 feet. Had either of these been available, the crew would have been aware of excellent weather at Karratha and identified it as the obvious reliable diversion away from an area where present weather was difficult to obtain and updated forecasts to correct the seriously misleading ones initially issued were not available.   

• Network Aviation’s Diversion Procedures

The forecast predeparture conditions for Paraburdoo required 60 minutes holding fuel but no alternate. On arrival in the vicinity of their destination, the crew encountered two unforecast weather hazards: deterioration of the cloud base below their landing minima, and the lack of an improvement within the 60 minute period on which the despatch criteria were founded. There was a SOP which limited the number of missed approaches to two but the Investigation considered that “a prescriptive diversion decision-making procedure was necessary." The limit on missed approaches did not provide guidance to crew to brief diversion options before arrival or on encountering unforecast weather at their destination. This absence of decision-making guidance was considered to have “increased the risk that flight crew would not be prepared for a diversion."

• Risk Management - Descent Below Approach Minima

The operator had no directly applicable risk assessment for flight crew continuing below the instrument approach procedure minima. Their CFIT avoidance relied on preventive risk controls such as visual reference and human performance for monitoring, detecting, and correcting problems to maintain situational awareness. However other risk management work on operations in adverse weather conditions, including lack of visual reference were noted to focus on contributing factors to CFIT rather than risk controls. Although the operator’s arrival briefing and approach checklist was “designed to enhance situational awareness and therefore reduce the likelihood of an unintentional descent below the minimum altitude," it was considered that “reliance on human performance as a control to monitor, detect and correct problems within a risk assessment can result in an inherently unsafe system." It was considered that any human performance safety requirement associated with a specific threat should be managed by appropriate controls such as training, procedures, and warning devices. But in this case, the need for the operator and its flight crew to effectively manage the consequences of unforecast instrument meteorological conditions below minima which could arise due to the development of a fuel-critical situation at a destination was considered to be unaddressed.

• Indication of urgency in requests for ad hoc weather updates 

The Investigation considered that the crew’s failure to associate their request for a Newman weather update with urgency was inappropriate and that inclusion of "minimum fuel" in such a request would have been appropriate. Timely provision of the requested information might have resulted in an alternative course of action which, due to the delayed response, was no longer relevant.    

Seven Contributing Factors, two of which were classified as Safety Issues (and are identified as such) were formally documented based on the Findings of the Investigation as follows:

• The flight crew lost confidence in their flight plan weather forecasts after two missed approaches at Paraburdoo Airport. Without immediate access to actual weather information, they elected to conduct further approaches instead of diverting.
• After the third missed approach, the flight crew had insufficient fuel to divert to a suitable airport and were committed to landing in conditions below their landing minima due to the deteriorating cloud base.
• The actual weather conditions encountered by the flight crew on arrival at Paraburdoo Airport were worse than the flight plan forecast, below the landing minima and deteriorating. This event was difficult to forecast accurately due to the lack of observed lower cloud, satellite imagery, and meteorological modelling limitations. 
• The aircraft was not fitted with an operational aircraft communications addressing and reporting system (ACARS) and was out of range of the Meekatharra automatic en route information service (AERIS) while holding at Paraburdoo Airport. Therefore, the flight crew relied on air traffic control to access actual weather information for alternate aerodromes. 
• Paraburdoo Airport did not have a means of detecting the moisture content in the atmosphere above the surface. This increased the risk that low clouds below the instrument approach landing minima might not be forecast.
• Network Aviation did not provide their flight crew with a diversion decision-making procedure for the circumstances where their flights encountered unforecast weather below landing minima. This increased the risk that their flight crew would not anticipate and be adequately prepared for a diversion [Safety Issue AO-2021-048-SI-01] 
• Network Aviation did not include the threat of unforecast weather below landing minima in their controlled flight into terrain risk assessments. This increased the risk that controls required to manage this threat would not be developed, monitored, and reviewed at a management level. [Safety Issue AO-2021-048-SI-02]

Two Other Factors that Increased Risk were also identified:

• The flight crew did not convey a sense of urgency to air traffic control when they requested the actual weather information for Newman Airport. This, combined with the controller's workload at the time, resulted in a delay of about 15 minutes before the information was provided. However, Newman Airport had a holding fuel requirement, with which the flight could not comply. As the actual weather did not include an improvement of conditions, it was considered unlikely that this information would have influenced their decision to divert. 
• The Newman Airport AWIS cloud and weather data groups were not available at the time the flight crew requested the latest weather from air traffic control. While this did not influence the flight crew’s decision to remain at Paraburdoo, it increased the risk that a deterioration in the cloud base below the forecast conditions at Newman would not be broadcast by air traffic control to airborne aircraft as a hazard.   

Safety Action taken by Network Aviation in respect of the event was noted as having included, but not been limited to the following actions, the first four of which addressed the two Contributing Factors classified as "Safety Issues" and resulted in them being formally closed prior to the publication of the Investigation Final Report.

• Created a Fokker F100 Company Procedures Manual which incorporated standard prepopulated diversion procedure information for their F100 destinations.
• Amended their Fokker F100 FCOM arrival briefing procedure to raise awareness around fuel status and increase flight crew coordination. Where alternate fuel requirements were previously only briefed "if applicable," it is now mandatory for all arrival briefings to include the minimum fuel required to divert to an alternate.
• Amended their flight plan format to include an alternate summaries section at the top of each flight plan for 2 alternate aerodromes. While this was previously provided for flight plans that legally required an alternate aerodrome, it is now provided for all flight plans.
• Updated their CFIT risk assessments to capture the threat of adverse weather.
• Issued an updated internal Safety Advisory Notice to their pilots which highlights the operating parameters and limitations associated with AWIS.
• Amended their Company Fuel Policy to mandate additional alternate fuel requirements for nominated airports with airport classification based on alternate availability, instrument approach availability, aerodrome forecast reporting/historical accuracy, local mesoscale weather phenomena and surrounding topography/terrain.
• Provided access for pilots operating to nominated airports to internal company meteorologists.
• Updated their Company Aerodrome and Route Data Manual to add new sections on weather planning tools and resources, and on the limitations of ceilometers and visibility meters installed in automatic weather information stations.
• Enhanced the company’s Training Reference Library for pilots to support improved knowledge and decision making with additional content on fuel management, threat management and contingency planning, time management in areas of vulnerability, and pilot-in-command responsibilities.

In Conclusion, a Safety Message based on the Investigation Findings was as follows:

Adverse weather conditions may not be experienced in the Australian environment to the same extent as they are in other countries. However, these events have been identified as contributing factors to incidents and accidents throughout aviation history and have been a driver for numerous safety initiatives. Therefore, it is important for all operators to consider how unforecast weather will be managed and ensure it is reflected in their risk management so that safety assurance activities can review how effectively it is managed and provide feedback for management review.

The Final Report was released on 24 March 2023. 

Related Articles

• Aircraft Load and Trim
• Weather Forecast
• Aerodrome Weather Information Service (AWIS)
• METAR
• Cloud
• Visual References
• Missed Approach
• Area Navigation Systems
• Minimum Descent Altitude/Height (MDA/MDH)
• Aerodrome Operating Minima (AOM)
• Fuel - Diversion to Weather Alternate