The aircraft, operating a scheduled passenger flight from Singapore to Sydney, landed at Sydney on runway 16R at 0525 Eastern Standard Time (EST) during curfew hours (All times are EST unless otherwise stated).
The Bureau of Meteorology (BOM) issued a terminal area forecast (TAF) for Sydney Airport at 2051 on 14 October 1997 for a 24-hour period commencing at 2200. The forecast indicated that the weather at Sydney would be suitable for an approach and landing, with the wind from 290 degrees at 8 kts. The forecast also indicated that from 0400 the wind would change direction to 240 degrees and that the strength would increase to 15 kts with gusts to 25 kts.
The Sydney Airport Weather Briefing issued to the operator by the BOM at 1745 on 14 October 1997 covered the TAF period from 1600 for 24 hours and indicated that there was a 20% chance that the change in the wind would be to a southerly direction.
The crew was aware of the TAF information at the pre-flight briefing at Singapore. As the available forecasts indicated that conditions would be acceptable for the aircraft to make an arrival at Sydney using runway 34L, there was no requirement to carry additional fuel other than company required variable and fixed fuel reserves. This was in accordance with normal company operating procedures and fuel planning policy.
The flight departed Singapore at 2217 (2017 local time) and the flight plan indicated that the aircraft would arrive in Sydney at 0456. During the flight, the crew monitored the hourly meteorological information broadcasts (VOLMET) and received routine meteorological (METAR) reports, which were based on Trend Type Forecasts (TTF), through the Aircraft Communication Addressing and Reporting System (ACARS) to keep themselves appraised of current and projected weather conditions at Sydney.
Trend Type Forecasts consist of aerodrome weather reports which contain a statement of trend. They are issued at 30-minute intervals and describe significant changes expected to occur during a 3-hour period. TTFs supersede aerodrome forecasts and the VOLMET information.
From 0130 the TTF for Sydney Airport included details of the south-westerly change expected at 0400. At 0333 a TTF was issued which indicated that the wind at Sydney was 200 degrees at 14 to 18 kts. This TTF, which the crew received via the ACARS, was appended with the term NOSIG, which indicated that there was no significant change expected within the next 3 hours. The TTF issued at 0403 indicated that the wind was 190 degrees at 7 to 12 kts and again included the term NOSIG.
The 0431 TTF reported the wind as 190 degrees at 17 to 24 kts. These conditions were unacceptable for a landing on runway 34L as the maximum certified tailwind of 15 kts for this aircraft would be exceeded. A special aerodrome forecast was issued 3 minutes later which reported the wind strength as 21 to 31 kts, with a resultant increased downwind component for a landing on runway 34L.
During aircraft operations, a point in the flight is reached where the crew need to make a decision to continue to the destination airport based on the weather and other conditions prevailing at that time. If conditions are not acceptable for arrival at the destination airport, the aircraft must proceed to an alternate airport. This point is usually designated as the decision point alternate (DPA). The DPA for this flight was Parkes NSW, with the alternate aerodrome nominated in the flight plan as Melbourne. At 0422, Melbourne Air Traffic Control (ATC) identified the aircraft's position on radar as 173 NM from Parkes.
The automatic terminal information service (ATIS) for Sydney was updated at 0424. This update reported that the wind direction was from 170 degrees and the strength was 10 to 20 kts with gusts to 25 kts and a maximum downwind component of 25 kts on runway 34L. This change in the ATIS was passed to the crew at 0426 and to two other international aircraft approaching Sydney.
The crew of the incident aircraft acknowledged that they had received this information. Shortly after, the crew advised ATC that their latest approach time to Sydney would be 0540. They also advised ATC that they had insufficient fuel to hold until 0600. The aircraft reached Parkes at 0444, 18 minutes after the new ATIS was broadcast, and continued towards Sydney.
In response to a query from ATC regarding diverting to Brisbane, the crew re-calculated the fuel status of the aircraft. Because the aircraft had passed the DPA, Melbourne was no longer a suitable alternative destination as there would be an excessive headwind en route. The crew advised ATC that if they proceeded to Brisbane immediately, they would have sufficient fuel. ATC asked the aircraft to stand by. Over the next 4 minutes ATC coordinated other traffic including aircraft entering holding patterns at Bindook. ATC subsequently asked the crew whether they intended to divert to Brisbane and the crew advised that they were now unable to do so as they had insufficient fuel. The fuel required to divert to Brisbane from this point was calculated by the crew to be 14,000 kg and there was only 13,200 kg remaining on board.
The crew informed ATC of the aircraft fuel status and that they would be proceeding to Sydney. ATC advised the crew that if they could not hold until 0600 and would therefore land during the curfew, they would have to declare an emergency. ATC then asked the crew to confirm that this was what they wished to do, to which the crew agreed. ATC then processed the aircraft ahead of the other preceding aircraft. The crew did not use the standard international phraseology to declare the emergency.
The crew again notified ATC that they could hold until 0540. ATC advised the crew that there would be no difference if they landed before this time as they would be landing on runway 16R prior to the lifting of the curfew.
During descent into Sydney, the crew assessed the possibility of making an approach to runway 34L, as the wind information from the aircraft Flight Management System (FMS) indicated that the wind still favoured an approach to runway 34. Information provided from Sydney Tower on the actual wind at the runway threshold precluded a landing on this runway. The aircraft landed on runway 16R at 0525, with more than the minimum fuel reserves in accordance with company policy.
In this occurrence, the crew of the aircraft was aware at the time of flight planning that a change in the direction and strength of the wind was expected before their arrival at Sydney. However, this change did not present problems for the crew at the flight planning stage, as the forecast conditions were still acceptable for a landing on runway 34L. During the flight, the changes in the wind direction and strength were still acceptable for the aircraft to use runway 34L until the change in wind velocity which was notified at 0426.
Until that time, the forecasts previously available to the crew contained errors of up to 70 degrees in wind direction. The only forecast which indicated a possibility that the wind would be southerly was the Sydney Airport Weather Briefing supplied to the operator on 14 October 1997.
The investigation was unable to determine why the crew did not act upon the change in wind information, or upon the implications of the resulting excessive downwind component for landing on runway 34L, before passing the DPA. By that stage little time remained in which to initiate a diversion to a suitable alternate airport. The crew did not request a diversion to Brisbane, and this, coupled with the ATC's delay in handling the aircraft after the DPA, eroded the time remaining in which a diversion was feasible.
At all times during the occurrence the aircraft had sufficient fuel to complete the flight to Sydney, and the aircraft landed with more than the minimum fuel reserves in accordance with company policy.
|Date:||15 October 1997||Investigation status:||Completed|
|Time:||0525 hours EST|
|State:||New South Wales|
|Release date:||01 November 1998||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure time||2217 hours EST|