Network Australia F100 at Paraburdoo on Nov 22nd 2021, descent below minimum without visual reference

Last Update: March 24, 2023 / 15:06:38 GMT/Zulu time

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Incident Facts

Date of incident
Nov 22, 2021


Flight number

Aircraft Registration

Aircraft Type
Fokker 100

ICAO Type Designator

Airport ICAO Code

A Network Aviation Australia Fokker 100, registration VH-NHV performing flight QF-1616 from Perth,WA to Paraburdoo,WA (Australia) with 92 passengers and 5 crew, was on approach to Paraburdoo's runway 06 but went around at 07:44L (23:44Z Nov 21st). The aircraft climbed to 5000 feet and positioned for an approach to runway 24 but again needed to go around. The aircraft climbed to 4000 feet and attempted another approach to runway 06 but again needed to go around (3rd time). The aircraft climbed to 6500 feet and positioned for an approach to runway 24 and continued to a landing at 08:44L (00:44Z) although at minimums no visual contact had been established.

The ATSB reported: "During a fourth attempt at an instrument approach at Paraburdoo Airport, the flight crew continued the descent below the approach minima before becoming visual and landing. As part of the investigation, the ATSB will interview the flight crew, review cockpit voice recorder and flight data recorder data, operating procedures, and flight planning information." The occurrence was rated a serious incident and is being investigated, a report is estimated for the 3rd quarter of 2022.

On Mar 24th 2023 the ATSB released their final report concluding the probable causes of the serious incident were:

Contributing factors

- 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 continuing 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 were reliant 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 cloud 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)

- 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)

Other factors that increased risk

- 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 offered. However, Newman Airport had a holding fuel requirement the flight could not comply with and as the actual weather did not include an improvement of conditions it was unlikely that this information would have influenced their decision to divert.

- The Newman Airport automatic weather station 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.

The ATSB analysed:


On the morning of 22 November 2021, a Network Aviation Fokker Aircraft F100, registered VH-NHV and operating as flight QF1616, departed Perth Airport on a scheduled passenger service to Paraburdoo Airport, Western Australia. On arrival at Paraburdoo, the flight crew conducted 3 missed approaches due to unforecast low cloud. On the fourth approach, the flight crew continued the approach below the landing minima without visual reference to the runway due to the aircraft’s fuel state.

This analysis will discuss the flight crew’s decision not to divert, the eventual landing below minima, and the reason for the unforecast low cloud. The delay in an air traffic control weather update, and limitations associated with in-flight access to weather while holding at Paraburdoo and weather forecasting at the airport, will also be discussed. It will also consider the operator’s procedural guidance and risk management for unforecast weather.

Decision not to divert

After downloading and reviewing their flight plan before take-off, the flight crew noted they had a 60-minute holding fuel requirement for Paraburdoo. However, both the mean and holding weather conditions indicated the lowest cloud was forecast to be above their landing minima. Therefore, they departed Perth with the expectation of landing from their first approach. This expectation was likely reinforced by the automatic weather information service (AWIS) broadcast prior to top of descent, which indicated the lowest cloud was 2,100 ft above the airport. Consequently, their first missed approach at Paraburdoo was unexpected.

The 0730 AWIS update during the descent indicated that low cloud had started to develop at 500 ft above the aerodrome, which was below their landing minima. However, the concurrent air traffic broadcasts on the other radio may have interfered with the flight crew hearing this information as the captain reported that the QNH was the only change noted. Since an accurate QNH must be obtained within 15 minutes of commencing an approach for the minima to be reduced by 100 ft, it was likely that this was their reason for listening to the AWIS during the descent.

When they conducted their first approach, the flight crew momentarily became visual with the runway but realised they would have been too steep to attempt the landing. However, the combination of the visual contact and tailwind on the first approach, provided them with confidence that a second approach to the opposite runway would be successful. Further, the cloud they encountered on the first approach was lower than forecast, which suggested to them that the first approach was likely flown in the worst of the expected conditions. They did not consider at this stage that the conditions might worsen. Therefore, they elected to immediately conduct a second approach, which was also unsuccessful due to low cloud obscuring the runway.

It was after the second missed approach that the flight crew realised the weather was more concerning than expected. At this stage, the deterioration in the actual conditions at Paraburdoo likely resulted in them losing confidence in their flight plan weather forecasts for decision-making purposes.

The weather reports for the airports under consideration for diversion by the flight crew indicated that Karratha Airport was the only suitable diversion. After the second missed approach, the flight management computer (FMC) indicated they were at minimum fuel to divert to Karratha, but the captain was cognisant that this did not allow for the winds they might experience or for an instrument approach on arrival at Karratha if required.
In this case, they could not determine if they could reach Karratha with their fixed fuel reserve remaining. Consequently, without knowledge of the actual weather conditions, they elected to disregard Karratha as an option.

Instead, the flight crew requested a weather update for Newman Airport since it was closer, and another aircraft had landed there recently. However, the captain was aware the forecast had a holding requirement and was reluctant to commit to a diversion unless the actual conditions were better than forecast. Solomon Airport was also considered after the third missed approach but was disregarded due to having a higher landing minima than Paraburdoo.

Therefore, as they were still within their 60-minute holding fuel period and did not have immediate access to actual improved weather conditions elsewhere, the flight crew elected to conduct further approaches at Paraburdoo.

Landing below minima

The ATSB’s review of their estimated fuel load found that the flight crew likely had sufficient fuel to divert to Karratha or Newman immediately after their second missed approach, but not after their third missed approach. According to the forecasts and actual conditions, Karratha was suitable, but Newman was not, and an immediate decision was required to divert to Karratha. However, it was only after the second missed approach that the flight crew started to discuss diversion options and the fuel consumption during this period consequently precluded Karratha as an option.

After their third missed approach, a diversion to Solomon was their only other option. However, as the lowest landing minima at Solomon was higher than at Paraburdoo, they disregarded it. At the time, the cloud base at Solomon was below the minima and therefore it would not have been a suitable diversion if the flight crew had received the latest actual weather. Consequently, the flight crew were committed to conducting a fourth approach at Paraburdoo.

Before they commenced their fourth approach the flight crew briefed their plan and duties, and their contingency plan if the approach became unsafe. They subsequently descended below the runway 24 MDA of 584 ft above aerodrome level without visual reference on the approach. On achieving their visual reference at about 293 ft, the aircraft was stable on the glidepath and close to the extended runway centreline, which enabled them to land without further incident, 57 minutes after their first missed approach.

Cloud base

On the night prior to the incident flight, there were no meteorological observations from the Pilbara region of persistent low cloud. In addition, there was a layer of mid-level cloud overnight that should have limited the overnight surface cooling and had also obscured satellite imagery of any low-level cloud. Therefore, the presence of scattered cloud at 1,000 ft above aerodrome level at the surrounding aerodromes at 0200 was used as the justification for forecasting mean conditions at Paraburdoo of scattered cloud at 1,000 ft, with TEMPO conditions for broken cloud at 1,000 ft. This was above the flight crew’s landing minima for runway 06 and 24 of 604 ft and 684 ft respectively.

There was also an expectation that surface heating would lift the cloud base after sunrise. However, the lifting trend in the modelling did not occur and the cloud base lowered, remaining below the highest alternate minima from 0730 for 3 hours 26 minutes.

Distinct from the forecast conditions, at 0730, 16 minutes before the first missed approach, scattered cloud at 500 ft was reported by the automatic weather station (AWS). This deteriorated to broken cloud at 400 ft before the last approach. The AWS was still reporting broken cloud at 400 ft at 0900, 17 minutes after the aircraft landed. This deterioration was consistent with the flight crew’s observations that they experienced low cloud at the approach minima for all 4 approaches, and broadcast after landing that patches of low cloud were present at 250-300 ft.

It was likely that evaporation of rainfall added moisture to the atmosphere (wet bulb effect), as indicated by a reduction in the reported visibility from greater than 10 km at 0730 to 6,000 m at 0751. While the surface wind had not yet backed around to the west, the tailwind component reported by the flight crew on their first approach to runway 06 suggested the winds above the surface already had a westerly component. Airflow from the west is forced to rise over the terrain to the west of the airport and will cool, which results in the development of low cloud if the air becomes saturated (orographic uplift). Therefore, the low cloud that developed below the forecast conditions, was likely a combination of moistening of the airmass from rainfall and orographic uplift from the local terrain.

These conditions were considered difficult to forecast due to the absence of low cloud observed on the evening prior, any low-level cloud being obscured on the satellite imagery, and the lifting trend in the modelling not occurring. This discrepancy between the forecast and actual conditions resulted in the flight crew losing confidence in their flight plan aerodrome forecasts for diversion decision-making purposes, and initially misled them to believe that conditions would not deteriorate further after their first missed approach.

In-flight access to weather information

A decision to divert is a procedure-based decision-making exercise, which is also known as rule-based decision-making. This is dependent on the situational awareness or knowledge of the problem, and knowledge of options (Flin, O’Connor, Crichton, 2008). When the flight departed Perth, the flight crew had incorrect knowledge of the weather situation that would unfold at Paraburdoo when they arrived. Although they passed within range of the Meekatharra automatic en route information service (AERIS), which would have provided them with the current weather for Karratha, there was no operational need for it at that stage, based on their assessment of the forecast conditions.

After the second missed approach, the flight crew’s discussions and actions indicated they had updated their assessment of the situation and were now actively seeking additional information about the weather conditions. This included the Paraburdoo AWIS (which was checked before each approach), air traffic control, and the Paraburdoo safety car officer. At this stage, they were holding at about 4,100 ft, which meant they were out of range of the Meekatharra AERIS, which required an altitude of about 36,500 ft to receive the broadcast.

The aircraft was fitted with the hardware for the aircraft communications addressing and reporting system (ACARS), which could be used to immediately access current weather information. However, the system was not operational, and therefore could not be used. If the system had been operative, they would have required a satellite link to use it, as they were holding below the required altitude of at least 11,000 ft to receive information from the nearest VHF datalink service at Newman. Therefore, with no other means to obtain current weather information while holding at Paraburdoo, the flight crew were reliant on air traffic control (ATC) to access weather information for alternate aerodromes.

If the flight crew had access to updated weather information using the AERIS or ACARS, it would have informed them that the cloud base was above 10,000 ft and visibility was greater than 10 km at Karratha. This would have indicated that Karratha was a suitable diversion location. However, without current weather information for alternative aerodromes, the flight crew elected to remain at Paraburdoo.

Atmospheric data

During the incident, a rain band and associated middle and high-level cloud was observed across north-western Australia by the Bureau of Meteorology (BoM). Their model traces had indicated saturated levels through to near to the surface. However, modelling in northern Australia was subject to false alarms for widespread low cloud. Therefore, some form of surface verification and/or satellite observations were required for the BoM to have confidence in the modelling. On the night prior to the incident, mid-level cloud made it difficult to utilise satellite observations to observe low cloud and confirm the modelling.

Light rain or drizzle had been falling at Paraburdoo. However, the extent of the rain was uncertain as Paraburdoo was outside the optimal range for the nearest weather radar stations. Therefore, it appeared clear on their weather radars at the time of the incident, despite the presence of low cloud and rain.

According to the BoM, the depth of moisture through the atmosphere is important in determining the potential for low cloud development. The sources available to indicate the depth of moisture are weather balloons and aircraft meteorological data relay (AMDAR). Data obtained from weather balloons allow forecasters to plot an aerological diagram and forecast cloud bases and tops.

However, the nearest weather balloon stations were more than 160 NM from Paraburdoo and may not necessarily be representative of the conditions experienced at Paraburdoo. Furthermore, as Paraburdoo was not part of the AMDAR network, no AMDAR profiles were available to support the BoM forecasts for Paraburdoo.

The accuracy of forecasting is dependent on the data available. As Paraburdoo did not have the means to provide forecasters with a vertical profile of the moisture through the atmosphere, and satellite imagery was not available due to being obscured by mid-level cloud, the forecast was dependent on observations at other airports in the region. Therefore, the lack of atmospheric measurements increased the risk of an inaccurate projection of the conditions for Paraburdoo including unforecast low cloud below the instrument approach landing minima. While the current BoM plans for upgrading weather balloon and weather radar stations around Australia do not include Paraburdoo Airport, the ATSB did not identify a trend from the last 10-years of data associated with this airport to warrant a safety issue at this stage.

Diversion procedure The forecast conditions for Paraburdoo required 60 minutes TEMPO holding fuel, but no alternate was required. Despite this, the flight crew were expecting to obtain visual reference with the runway before reaching their minimum descent altitude for the approach. This expectation was likely reinforced by the AWIS recording before top of descent, which indicated the lowest cloud base was 2,100 ft above the aerodrome. However, on arrival, the flight crew were confronted with 2 unforecast weather hazards. The cloud base had deteriorated below their landing minima, and it did not lift within the 60-minute TEMPO period.
As discussed previously, a diversion is a procedural decision-making exercise, which requires knowledge of both the problem and the options available (Flin, O’Connor, Crichton, 2008).

Therefore, a diversion decision-making procedure should serve the purposes of guiding the flight crew to correctly assess the problem and then select an appropriate course of action.

The operator had published a procedure, which limited the number of missed approaches to 2, but they did not believe a prescriptive decision-making procedure was necessary. However, even after the first missed approach, the flight crew were expecting to land from their second approach and there was no discussion of the limits to conducting missed approaches nor consideration of their fuel reserve for a diversion.

After the second missed approach, the flight crew only had a few minutes in which to decide to divert to Karratha, which was the nearest suitable alternate airport. However, they had not briefed this option. Therefore, instead of committing to a diversion after the second missed approach, they entered a holding pattern and started to diagnose the actual weather conditions and their options.

The operator’s limit to missed approaches did not provide guidance for flight crew to brief their divert options before arrival or on encountering unforecast weather at their destination. The arrival briefing procedural guidance from the International Civil Aviation Organization (Doc 8168, 2018) included ‘alternate aerodromes and fuel considerations’, and while this was within the context of ‘relevant conditions’, unforecast weather is a hazard frequently reported to the ATSB and that has been the subject of previous accident and incident investigations. In this case, if the flight crew had briefed their divert options before arrival, they would have been better placed to manage the unforecast weather conditions they encountered at Paraburdoo. Therefore, a diversion procedure should be considered within an organisation’s risk controls and the absence of this decision-making guidance increased the risk that flight crew would not be prepared for a diversion.

Risk management

The 3 United Kingdom Civil Aviation Authority’s (CAA) bowtie risk assessments for controlled flight into terrain (CFIT) were largely retained by the Qantas Group Flight Operations Steering Committee (FOSC) and subsequently Network Aviation, with minor amendments. One of the notable amendments was the replacement of the CAA CFIT 3.1 threat 8: Flt crew continue approach below the MDA/DH without visual reference with the FOSC CFIT 3.1 threat 8: Flt crew operate below the appropriate minimum altitude (exc. instrument approach). This was considered by the operator to be the closest risk assessment to the incident.

It was also noted that the operator’s CFIT 3.2 and 3.3 risk assessments for instrument approaches had not captured CAA CFIT 3.1 threat 8. Consequently, there were no weather-related threats identified in the operator’s CFIT bowties. In which case, there was no requirement to identify controls or treatment plans to manage these threats, despite a recent CFIT research and analysis report finding that adverse weather was cited as a contributing factor in 51% of accidents (IATA, 2018).

The operator’s CFIT threats relied on preventive risk controls such as visual reference and human performance for monitoring, detecting and correcting problems to maintain situational awareness.

While the latter appeared to be inherited from the UK CAA bowties, research conducted by the International Air Transport Association indicated that operating in adverse weather conditions, poor visibility, and a lack of visual reference were considered contributing factors or threats to CFIT rather than risk controls. It was also noted that other procedural controls were used by the operator, but not included in the bowtie risk assessment. These included their arrival briefing and approach checklist, which, according to International Civil Aviation Organization (ICAO) Doc 8168 (2018), are designed to enhance situational awareness and therefore reduce the likelihood of an unintentional descent below the minimum altitude.

A reliance on human performance as a control to monitor, detect and correct problems within a risk assessment can result in an inherently unsafe system. If there is a human performance safety requirement associated with a specific threat, then this should be managed with the appropriate controls, such as training, procedures, and warning devices, as indicated by the International Air Transport Association CFIT mitigation strategies (2018) and ICAO (Doc 9683, 1998). They would then be subject to the safety assurance activities for that risk assessment.

The key environmental threat from this investigation that operators and flight crew need to manage is unforecast instrument meteorological conditions below minima at the destination. While forecast weather below minima is routinely effectively managed with a prescriptive ruleset, unforecast weather may be more likely to result in the need for an approach below minima without visual reference due to the development of a fuel-critical situation. Therefore, the absence of this threat from the operator’s CFIT risk assessment increased the risk that controls required to manage this threat would not be developed, monitored, and reviewed at a management level.

Weather update delay

Although the flight crew were aware that Newman had similar conditions to the Paraburdoo forecast, including a 60-minute holding fuel requirement, another aircraft had landed there between QF1616’s first and second missed approaches. This suggested to the flight crew that Newman might be a suitable diversion. As such, the captain informed ATC that they had conducted a second missed approach due low cloud at Paraburdoo and requested the latest weather for Newman. However, there was no urgency associated with this request and ATC asked them to standby for a response. Following this request, the flight crew and ATC diverted their attention to their other tasks, which included traffic inbound to Paraburdoo.

There was a delay of about 15 minutes before ATC queried if the flight crew still required the weather for Newman. At this stage, they had conducted a third missed approach and were likely below the minimum fuel required to divert to Newman, therefore the captain declined. While this delay precluded the flight crew considering the option of a diversion to Newman, both the cloud and weather data groups for Newman were not available for the period from 0600-1000. Without a meteorological observer at Newman, the latest METAR was the only current weather ATC could have provided the flight crew. In addition, the captain was reluctant to divert to another airport that had a holding fuel requirement they could not meet and might be subject to a similar weather pattern as Paraburdoo, unless the actual weather was better than forecast. As the current METAR did not provide an improvement to the forecast, it was unlikely that the provision of the latest weather information would have influenced the flight crew to divert to Newman and the delay was not considered contributory to the incident.

Despite this, ATC was the only option for the flight crew to obtain current weather for an alternate airport and the report of missed approaches at Paraburdoo associated with the request for the latest weather for Newman suggested this was likely a time-critical request. While the flight crew were within their TEMPO fuel holding period at Paraburdoo, they were approaching a fuel critical situation for a diversion to Newman. In this scenario, the inclusion of ‘minimum fuel’ with their request for the latest Newman weather could have reduced the likelihood of a delay, but probably would not have changed the outcome.

Newman automatic weather information service

The Airservices Australia new filtering system for SPECI reports was dependent on the conditions that trigger such reports being detected at the aerodrome. On the morning of the incident flight, there were 11 weather reports issued from the Newman AWS from 0600-1000. This included 2 SPECI reports for a reduction and subsequent improvement in visibility at 0934 and 0944. However, the cloud and weather data groups were not available throughout this period, which meant that Newman could have entered SPECI conditions undetected during this period.

As there was a delay in the information and the captain subsequently declined the weather update for Newman, this did not influence their decision to remain at Paraburdoo. However, if a SPECI condition is not detected at the source by an AWS, unforecast weather conditions may not be captured and disseminated by ATC to airborne aircraft as a hazard. While this is not a substitute for flight planning and in-flight weather update requests before reaching a point-of-no-return, the broadcast of unforecast SPECI conditions may provide a timely alert to flight crew to avoid a fuelcritical situation developing.

YPBO 220300Z AUTO 30004KT 9999 // SCT013 SCT018 OVC032 24/21 Q1012=
YPBO 220256Z AUTO 30004KT 9999 // SCT013 BKN018 OVC032 24/20 Q1012=
YPBO 220230Z AUTO 27004KT 9999 // BKN011 OVC016 23/20 Q1013=
YPBO 220200Z AUTO 30005KT 9999 // OVC009 22/20 Q1013=
YPBO 220200Z AUTO 30005KT 9999 // OVC009 22/20 Q1013=
YPBO 220130Z AUTO 25005KT 9999 // SCT006 OVC011 OVC015 22/19 Q1013=
YPBO 220100Z AUTO 24007KT 9999 -SHRA BKN004 OVC009 OVC017 21/20 Q1013=
YPBO 220100Z AUTO 24007KT 9999 -SHRA BKN004 OVC009 OVC017 21/20 Q1013=
YPBO 220030Z AUTO 26007KT 7000 -SHRA BKN004 BKN010 BKN013 21/20 Q1013=
YPBO 220000Z AUTO 33004KT 290V350 3000 -SHRA BKN008 OVC010 21/20 Q1013=
YPBO 220000Z AUTO 33004KT 290V350 3000 -SHRA BKN008 OVC010 21/20 Q1013=
YPBO 212351Z AUTO 34003KT 6000 -SHRA BKN008 OVC015 21/19 Q1013=
YPBO 212331Z AUTO 04004KT 9999 -SHRA SCT006 BKN015 BKN024 21/20 Q1013=
YPBO 212300Z AUTO 05007KT 9999 -RA BKN049 OVC054 20/19 Q1012 RERA=
YPBO 212214Z AUTO 05009KT 8000 RA SCT026 SCT039 BKN044 20/19 Q1012=
YPBO 212200Z AUTO 05009KT 4200 +RA SCT028 BKN039 OVC050 20/19 Q1012=
YPBO 212200Z AUTO 05009KT 4200 +RA SCT028 BKN039 OVC050 20/19 Q1012=
YPBO 212100Z AUTO 06006KT 9999 RA SCT050 BKN065 BKN075 20/19 Q1012=
Incident Facts

Date of incident
Nov 22, 2021


Flight number

Aircraft Registration

Aircraft Type
Fokker 100

ICAO Type Designator

Airport ICAO Code

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