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Summary

Summary

Sequence of events

On 6 April 2004, at about 0625 Eastern Standard Time, an Airbus A330-301 aircraft landed on runway 34L at Sydney aerodrome in weather conditions that were below the applicable landing minima1. The aircraft, registered VH-QPC, was being operated on an instrument flight rules (IFR) scheduled passenger flight from Perth to Sydney. During the latter stage of the flight unforecast fog developed at Sydney aerodrome, which resulted in the deterioration of visibility to below the landing minima.

The flight had been planned using a valid aerodrome forecast for Sydney, which predicted rain showers and visibility greater than 10 km, with 1 to 2 oktas2 of cloud at 1,200 ft and 5 to 7 oktas at 5,000 ft. Those weather conditions were above the Sydney alternate minima3 of 1,479 ft cloud ceiling and 6 km visibility. As there were no operational requirements due to the forecast weather conditions, the flight departed Perth without fuel being specifically carried for a diversion to an alternate aerodrome after an approach at Sydney.

The flight planned ?Designated Point All Engines Operating? (DPA)4, based on a diversion to Melbourne, was the IFR waypoint TOBOB, located 314 NM west of Sydney. Prior to TOBOB the crew obtained the 0400 and 0430 Sydney trend type forecasts (TTF). The TTFs were attached to the Sydney aerodrome weather reports and detailed the weather conditions expected to affect the aerodrome for the 3 hours following the time of the weather report. TTFs were routinely issued every 30 minutes for Sydney aerodrome and the 0400, 0430 and 0500 TTFs all indicated that, at the time of the aircraft?s estimated time of arrival (ETA), the visibility and cloud ceiling at Sydney would be above the alternate minima. The crew did not obtain the 0500 TTF. The aircraft passed the TOBOB position at 0518.

The crew commenced descent for Sydney at 0540 and, at about the same time, air traffic control (ATC) broadcast to aircraft that the Sydney automatic terminal information service (ATIS) had changed to include the remark that there was a fog bank to the north-west of the aerodrome. The ATIS was also reporting visibility greater than 10 km, with 1 to 2 oktas of cloud at 1,000 ft and 3,000 ft. The ATIS consisted of a continuous and repetitive broadcast of pre-recorded information about the actual weather conditions at the aerodrome.

The pilot in command reported that following receipt of the ATIS information, the crew obtained weather information about three aerodromes near Sydney; Williamtown, Richmond and Canberra. These aerodromes were available for use during non-normal operations (see Availability and selection of alternate aerodromes for more information). The pilot in command stated that, at the time, he considered the weather conditions at Williamtown might deteriorate to below the landing minima and Richmond was unavailable as the conditions were below the landing minima. He assessed Canberra as presenting potential difficulties due to the cloud ceiling being just below the alternate minima for runway 17 and just above the alternate minima for runway 35. In addition, the crew estimated that the fuel on board was insufficient to allow them to conduct a missed approach at Sydney and then divert the aircraft to Canberra. The pilot in command also stated that Canberra was a relatively unfamiliar aerodrome and he did not have any Notice to Airmen (NOTAM) operational information about Canberra.

The crew obtained the 0530 Sydney TTF soon after commencing descent. It indicated that, at the time of the aircraft?s ETA, there could be periods of up to 60 minutes when the visibility at Sydney would be 7,000 m in rain showers, with 5 to 7 oktas of cloud at 1,000 ft. These conditions were below the alternate minima, but above the special alternate weather minima of 400 ft cloud ceiling and 2 km visibility that applied to instrument landing system (ILS) approaches at Sydney. The aircraft was fitted with navigation equipment that allowed the use of the special alternate minima.

At 0555, as the aircraft descended through flight level 180 about 60 NM south-west of Sydney, ATC advised the crew that the Sydney ATIS had changed to include a hazard alert. This was in response to unforecast fog that had reduced the runway visual range (RVR)5 to 800 m. The ATIS also advised flight crew to expect ILS approaches to runways 34 Left (34L) and 34 Right (34R). One minute later, in response to that broadcast, the crew advised ATC that they required runway 16 Right (16R) for landing. This was due to the runway 16R ILS category one landing minima of 220 ft cloud ceiling and 800 m visibility being less restrictive than the runway 34L ILS category one landing minima of 270 ft and 1,500 m.

At 0558, ATC advised the crew that there would be a delay due to their requirement for an approach to runway 16R and instructed them to turn onto a heading of 230 degrees (taking the aircraft away from the aerodrome). One minute later, the crew broadcast a PAN6, declaring an urgency condition due to ?minimum fuel, require runway 16R for arrival?. The aircraft was then radar vectored for an ILS approach to runway 16R. The pilot in command stated that the PAN call was made because there was insufficient fuel to proceed to an alternate aerodrome approved by the operator for normal operations, ATC were vectoring the aircraft for a holding pattern and the weather conditions at Sydney were deteriorating at an unknown rate.

At about the same time, the crew of a Boeing 737 on final approach for runway 34L advised ATC that they could see the threshold and the first 1,000 m of the runway. The crew of QPC, being on a different radio frequency, did not hear that information, nor was it subsequently provided to them by ATC.

At 0604, in response to a request by ATC for the crew?s latest acceptable landing time at Sydney, they replied ?? time one eight [0618] and then we?d need to go straight to Canberra?. The pilot in command stated that a diversion to Canberra would have been the selected option only in the event that weather conditions at Sydney had deteriorated to below the landing minima. He also considered that a diversion would only ensure a ?minimum fuel state, at best?, upon arrival at Canberra.

At 0611, when the aircraft was about 17 NM north-north-west of the airport and tracking to intercept the runway 16R ILS localiser, the crew requested information about the visibility at the airport. After receiving a report from an approved observer in a motor vehicle positioned near the runway threshold, ATC advised the crew that the visibility on the runway 16R threshold was 400 m. The crew then requested the visibility on runway 34L. They were advised that the crew of a Boeing 747 approaching runway 34L ?reported visual at 1000 ft and he?s been visual all the way to 34L?. The crew of QPC then requested a vector ?for short final 34L? and were provided with radar vectoring for an approach to runway 34L.

The Boeing 747 landed on runway 34L at about 0614 and its crew reported to ATC that ??we were visual the whole way to touchdown, but I?d say this vis [visibility] at midpoint is a thousand metres or thereabouts and it?s rolling through to the south and thickening. It won?t be long before it will be a bit worse at the threshold at 34L?. The crew of QPC did not hear that information as they using a different radio frequency, but ATC advised them at 0615 that ?? the fog is now moving around at the airfield. I can?t guarantee you the same visibility as [the] company 747 of yours [that] landed on 34L?. Soon after, at 0617, one minute before the nominated divert time, ATC advised the crew of QPC that the RVR for runway 34L from the threshold was 2,000 m, which was 500 m more than the landing minima.

At 0622, the aircraft was established on the ILS approach for runway 34L. At about the same time, the crew of a preceding aircraft on approach to runway 34L conducted a missed approach because they were unable to see the runway lights. The controller passed that information to the crew of QPC. During the approach, the pilot in command of QPC saw the threshold of the adjacent parallel runway 34R and he advised ATC that he would need a right orbit onto the ILS of the adjacent runway to enable a landing. However, soon after, he decided to continue the approach to runway 34L as the aircraft was configured for an autoland. The pilot in command reported that he was concerned that if a missed approach was conducted and the aircraft was then manoeuvred for an approach to the adjacent parallel runway 34R, the heavy fog to the north may have moved across that runway during the next approach.

The aircraft was certified for autoland operations using the auto-flight system to control the aircraft during the approach and landing phase, and the crew had undergone the required training to conduct an autoland. The instrument landing systems for the various runways at Sydney were only certified to facility performance category one criteria, which meant that pilots were not permitted to continue approaches, including autolands, to runway 34L when the weather conditions were less than the specified category one landing minima.

The crew conducted a runway 34L ILS approach using the aircraft?s autoland capability and landed at 0625 in weather conditions that were less than the specified landing minima.

Civil Aviation Regulation (CAR) 257(5) specified that ?? if an emergency arises that, in the interests of safety, makes it necessary for an aircraft to land at an aerodrome where the meteorological minima is less than that determined for that aircraft operation at that aerodrome? then CAR 257(4) did not apply. CAR 257(4) stipulated that if an element of the meteorological minima for the landing of an aircraft at an aerodrome was less than that determined for the aircraft operation at the aerodrome, the aircraft was not to land at that aerodrome.

Availability and selection of alternate aerodromes

The aircraft operator provided information about aerodromes approved for A330 operations in the Route Manual Supplement (RMS), which was carried onboard the aircraft for flight crew use. If an aerodrome was approved for normal operations and the weather conditions were forecast to be better than the alternate minima, the aerodrome was classified as ?suitable aerodrome? and could be used as an alternate aerodrome for the destination. Brisbane, Coolangatta, Melbourne and Adelaide were the closest aerodromes that could be used as ?suitable aerodromes? for operations to Sydney.

The RMS also listed other aerodromes that were categorised as either emergency or adequate aerodromes that could be used during non-normal operations. Emergency aerodromes had runways of a sufficient length that could be used by A330 aircraft in an emergency situation. Nowra and Canberra were the closest emergency aerodromes to Sydney.

Adequate aerodromes met the requirements detailed in Civil Aviation Order 82.0, Appendix 2. If the weather conditions were forecast to be better than the specified ?adequate criteria?, an adequate aerodrome was considered to be a ?usable adequate aerodrome? and could be used by A330 aircraft following a critical system failure. The closest adequate aerodromes to Sydney were Williamtown and Richmond.

During the latter phase of the occurrence flight, the closest ?suitable aerodrome? was Melbourne and, once the aircraft flew past the DPA at 0518, the fuel on board was insufficient for a diversion to that aerodrome. When the crew became aware of the presence of fog near Sydney at about 0540, they obtained information about two adequate aerodromes, Williamtown and Richmond, and an emergency aerodrome, Canberra (see Sequence of events for the crew?s assessment of the weather conditions at these aerodromes).

The pilot in command stated that he considered that ATC had to be advised of an emergency condition in order to use an emergency aerodrome listed in the RMS. The operator also advised that the decision to divert to Canberra would have required the broadcast of PAN.

Aircraft fuel load

The aircraft departed Perth with 28,900 kg of fuel, which was 2,500 kg more than the minimum amount required by the operator?s approved fuel policy for the flight. The planned flight time from Perth to Sydney was 210 minutes and the fuel load gave the aircraft an endurance of approximately 315 minutes. As noted earlier, the aerodrome forecast did not require additional fuel, for either holding or a diversion, to be carried on this flight to Sydney.

The operator?s Flight Administration Manual (FAM) contained the fuel policy that specified the minimum mandatory fuel requirements approved by the operator for the operation of its aircraft. The FAM stated ?? it is recognised that there are occasions when a flight may pass DPA with the required fuel on board and a subsequent deterioration in forecast weather may then result in the minimum mandatory requirements ? not being met?.

After the occurrence, the operator calculated that the total amount of fuel required to divert the aircraft from a missed approach at Sydney to a landing at Canberra with reserves intact was 6,700 kg. Information from the aircraft?s flight data recorder showed that the aircraft landed at Sydney with about 6,900 kg of fuel remaining.

Meteorological information

The Bureau of Meteorology advised that fog at Sydney aerodrome was difficult to forecast as it was an uncommon event with between four and eight occurrences per year. Although the fog forecasting models had been upgraded in 1999, those models did not predict the formation of fog on the date of the occurrence. The classic fog scenario occurs when radiative cooling in the north-west area of the Sydney basin produces fog, which then moves to the aerodrome in a north-westerly surface airflow. For this airflow to form, several hours of clear sky is required to produce enough cooling so that the surface airflow uncouples from the gradient level airflow, which is 2,000 ft to 3,000 ft above ground level and may be moving in a different direction.

As the cloud was expected to persist during the morning of the occurrence, the duty operational meteorologist considered that the airflow uncoupling would not occur and the surface airflow would remain the same as the gradient airflow, which was from an east to north-easterly direction. At 0230, the high resolution computer forecasting models indicated precipitation and an east to north-east surface airflow. Although fog had formed in some western areas of the Sydney basin by 0330, the meteorologist considered that the rain showers near Sydney aerodrome would assist in mixing the slightly stronger east to north-easterly gradient airflow down to the surface airflow and hence reduce the risk of fog drifting in from the north-west.

The low-level cloud at the aerodrome cleared at about 0500, which coincided with the surface airflow tending to be from the north-west. About 40 minutes later fog was observed to the north-west of the aerodrome and soon after it started to move over the runways. The deterioration in visibility associated with the movement of the fog was rapid. A reduction in visibility from 2,000 m to 400 m was reported during an 11 minute period from 0552 to 0603. The fog did not clear until 0830.

The Canberra 0530 special aerodrome weather report (SPECI) obtained by the crew indicated that the wind was from the south at 3 to 4 kts, visibility was greater than 10 km, with 7 oktas of cloud at 2,100 ft above the aerodrome. The Canberra 0600 TTF was not obtained by the crew, but it did not vary significantly from the 0530 SPECI. According to the applicable Jeppesen Airport Chart, Canberra was available as an alternate aerodrome provided the cloud base above the aerodrome was not below 2,084 ft (2,144 ft for runway 17) and the visibility was not less than 6 km (7 km for runway 17). That minima was applicable with an actual QNH, which was available at Canberra, and was being broadcast on 116.7 MHz.

Provision of weather information to the flight crew

Airservices Australia (Airservices) was the air traffic service (ATS) provider. The procedures for the provision of weather information to flight crew by air traffic controllers were detailed by Airservices in the Manual of Air Traffic Services (MATS). The Aeronautical Information Publication (AIP), also published by Airservices, was an Australian operational document used by pilots. The information in the AIP that related to the provision of weather information was in accordance with the MATS.

The MATS required air traffic controllers to monitor and assess information from various reports. These included weather forecasts, amended weather forecasts and observations and reports that indicated the weather conditions at the destination aerodrome had deteriorated below the alternate minima. If that information was assessed to be of ?an unexpected and critical nature?, controllers were required to broadcast a hazard alert to flight crews.

At 0554, soon after the fog was observed moving over the aerodrome, the controllers amended the ATIS to include a hazard alert due to unforecast fog. The ATIS also advised pilots to expect an ILS approach to either runway 34L or 34R and that the RVR had reduced to 800 m in fog. This information was also broadcast at that time by the controller handling QPC.

A special aerodrome weather report (SPECI) was issued at 0603, and this report indicated that the visibility had reduced to 400 m in fog, which was below the landing minima of any runway at Sydney. The TTF appended to the SPECI indicated that these conditions would continue until 0800. The 0603 SPECI information was not passed to the crew of QPC. However, they became aware of the deterioration in the weather conditions at 0611 when ATC provided information about the RVR on runway 16R.

The RVR was assessed by approved observers in motor vehicles positioned near the runway thresholds. To determine the RVR, the observers counted the number of visible runway lights or identifiable features adjacent to the runway. This information was then broadcast to the aerodrome controller in the control tower. During the occurrence, there were observers in vehicles located near the thresholds of runways 16R, 34L and 34R.

Landing information, including RVR, was provided to flight crews either by controllers, or by the crews listening to the ATIS broadcast. The MATS section 5.1.11 contained instructions regarding the format of weather information provided in the ATIS. The MATS specified that, when the visibility was between 1,500 m and 800 m, the ATIS may report RVR information. It also stated that when visibility was 800 m or less, the RVR ?shall be reported? in the ATIS broadcast. The MATS and the AIP did not specify that the RVR information in an ATIS broadcast was to be for the touchdown zone of the runway in use.

When the ATIS was amended at 0554 to include the 800 m RVR information, the actual visibility at the touchdown zone of runway 34L was greater than that figure.

The ICAO Annex 3 ? Meteorological Service for International Air Navigation (Annex 3), contained the standards and recommended practices regarding the provision of metrological services in the aviation sector. Paragraph 4.7.4 of Annex 3 recommended that RVR observations should be made on precision approach runways for category one instrument approach and landing operations. Runway 16R and 34L at Sydney were category one precision approach instrument runways. ICAO Annex 14 ? Aerodromes defined a category one runway as ?? an instrument runway served by ILS ? and visual aids intended for operations with a decision height not lower than 60 m (200 ft) and either a visibility not less than 800 m or a runway visual range not less than 550 m?. Paragraph 4.7.2 of Annex 3 required that:

Runway visual range observations shall be representative of the touchdown zone and, depending on the category of operation for which the runway is intended and the length of the runway, of the mid-point and stop-end of the runway.

Following the amendment of the Sydney ATIS at 0554, the weather conditions continued to deteriorate with the visibility reducing to 400 m by about 0600. However, the next amendment of the ATIS was not until 0633. Requirements for the revision of ATIS information were covered in the MATS section 5.1.12. Paragraph 5.1.12.1 specified that when the current value of the visibility information was less than 1,500 m, controllers were to amend the ATIS as required if the value of the visibility was expected to vary and remain that way for at least 15 minutes.

Paragraph 5.1.12.2 of the MATS stated that in situations where controller workload precluded the amendment of the ATIS in accordance with the MATS requirements:

Tower controllers shall ensure that aircraft under their control are advised of sudden and perhaps unexpected changes to the aerodrome information, pending an amended ATIS.

Notwithstanding these requirements, there was no provision in the MATS for controllers, who were located remote from the control tower and who were passing ATIS information to flight crews, to be made aware of changes to the aerodrome information pending the updating and broadcasting of an amended ATIS.


1 The landing minima are the Civil Aviation Safety Authority (CASA) specified meteorological conditions of cloud ceiling and visibility. In order for an aircraft to land at an aerodrome, the actual weather conditions need to be at or above the landing minima.
2 Okta is a meteorological unit, equal to the area of one eighth of the sky.
3 Alternate minima are the cloud base and visibility values specified by CASA for a particular aerodrome such that, if the conditions are forecast to be worse than the alternate minima, the pilot in command must provide for a suitable alternate aerodrome.
4 The term DPA was used by the operator to indicate the point along the flight plan track that equated to the last position furtherest removed from the departure aerodrome from which an aircraft could divert to a nominated off-track alternate aerodrome. The minimum fuel required to be onboard at the DPA comprised the flight fuel to the alternate aerodrome, a variable fuel reserve, approach fuel, a fixed fuel reserve and holding fuel (if required).
5 The International Civil Aviation Organization (ICAO) Annex 3 - Meteorological Service for International Air Navigation defined runway visual range as '? the range over which the pilot of an aircraft on the centre line of a runway can see the runway surface markings or the lights delineating the runway or identifying its centre line'.
6 PAN is an expression, spoken three times in succession, used in the case of an urgency condition. ICAO Annex 10 - Aeronautical Telecommunications, Volume II, defined an urgency condition as '? a condition concerning the safety of an aircraft or other vehicle, or of some person on board or within sight, but which does not require immediate assistance'.

 
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