Description

On 25 October 2022, a Boeing 777-300ER (9V-SWH) being operated by Singapore Airlines on a scheduled international passenger flight from London Heathrow to Singapore Changi with an augmented flight crew encountered deteriorating weather conditions after initiating a weather diversion to Batam where four approaches were flown and a ‘MAYDAY Fuel’ declared before a landing was finally achieved by which time the fuel remaining had reached a level which was an unquoted amount “significantly below final reserve”.

Investigation

An Investigation was carried out by the Singapore Transport Safety Investigation Bureau (TSIB) on the basis of relevant recorded and submitted information. Relevant ATC recorded data were available but as all the relevant data on the CVR was not isolated after completion of the diversion, it was overwritten. The FDR was also not deactivated by the flight crew but was subsequently removed and relevant data were successfully downloaded. It  was noted that the 55 year-old Captain in command had a total of 14,371 hours flying experience of which 10,075 hours were on type and that the 31 year-old First Officer had a total of 2,261 hours, all of which were recorded as on type. The augmenting crew consisted of a cruise relief Captain but they were not present on the flight deck for the destination approach and were not required to be.

What Happened

The landing of all aircraft arriving at Singapore Changi in mid afternoon was disrupted by an area of thunderstorms which was moving southwards across the country and towards the eastern side of Batam Island where Batam airport was located. Although visibility at the airport was compatible with Cat 1 ILS approaches, directionally unstable wind conditions resulted in significant delays and a number of aircraft diverted as a result. 

The 13 hour flight from London had departed without uplifting any additional fuel beyond that on the operational flight plan because the forecast arrival weather was above landing minima and the crew were confident of a slight reduction in the planned track which would result in additional reserve fuel being available. However, they were aware prior to departure that the usual post-midday tropical convective storm activity was being forecast for the period which included their expected arrival time.

The flight proceeded normally until nearing the destination when, whilst still in the Kuala Lumpur FIR and with just under an hour to go until the scheduled arrival time, the flight was advised by Singapore APP that positioning for a landing on runway 20R could be expected. At that point, the crew stated that the FMC had indicated that the estimated fuel remaining after landing from a no-delay approach would be about 4,000 kg above the required 3,024 kg Final Reserve Fuel (FRF). However, four minutes later, ATC instructed the flight to begin holding because of a tailwind on Runway 20R and then advised all inbound traffic to expect a delay because of this. The two nominated destination alternates for the flight, Paya Lebar Air Base in Singapore and Senai International Airport just over the border with Malaysia at Johor Bahru were affected by similar convective activity although at that time, the Captain stated that based on weather radar returns, the conditions at the available and frequently used but not formally designated alternate Hang Nadim International Airport (Batam), just 16 nm away from Changi, had “appeared fine”.

After a further five minutes holding, ATC notified all inbound traffic that the runway in use had been changed 02L. Twelve minutes after this, the flight was transferred from the APP frequency to the ARRIVAL CONTROL frequency and thereafter was provided with radar vectors for such an approach accompanied by advice that there was heavy rain in deteriorating visibility - although the latter was not below Cat 1 ILS requirements - at the airport. The surface wind then returned to favouring runway 20 operations and after two aircraft had initiated go-arounds from 02L and another had discontinued its approach, ATC decided to temporarily suspend approaches in order to review how best to continue.

The inbound flight from London was directed to take up a hold and whilst routing to do so, the crew confirmed from the Batam ATIS that the airport there was still clear of the weather which was causing problems over Singapore and began considering a diversion there. ATC were informed that only one hold could be performed before the flight would be down to “emergency fuel” which was observed by the Investigation to have been a non-standard term with no meaning for ATC which did not appear in Singapore Airlines’ procedures. On the basis that the weather over Singapore was not improving, ATC therefore contacted Tanjung Pinang APP (responsible for traffic inbound to Batam) to initiate coordination pending the likelihood that the flight might wish to divert to Batam. The flight crew stated that they had been aware that with the aircraft at that time being about the same distance from Batam and Changi, a diversion there “would not aggravate the fuel situation”.

As the aircraft was about to complete its hold, the Captain asked ATC if there was any update and when advised that there was not, stated that they could fly a second hold after which they would need to divert to Batam if an approach was still not possible. As the second hold was completed, ATC instructed the flight to take up a radar heading which was taking them away from both Changi and Batam Airports and were told that approaches at Changi were still not being accepted and that their diversion to Batam had still not been approved. Shorty after this, the Captain advised ATC that they now needed to begin a diversion to Batam and followed this by taking over from the First Officer as PF. ATC acknowledged this and gave a radar heading of 180° to position the flight for a landing on Runway 22 at Batam whilst noting that the required diversion was not yet approved (three other inbound flights had already diverted to Batam and three more to alternate airports). As this vectoring towards the edge of Singapore ATC responsibility whilst awaiting clearance from Indonesian ATC was occurring, the First Officer informed ATC that they were “down to minimum fuel” and when the response was that the diversion had still not been approved, the Captain transmitted “MAYDAY Fuel” with the estimated fuel remaining on landing at Batam being estimated as equivalent to the calculated FRF.

Transfer to Tanjung Pinang APP soon followed and on checking in, the flight was informed that they had priority for landing at Batam. The PF Captain temporarily took over ATC communications to allow the First Officer to set up the aircraft systems and provide information in preparation for an approach at Batam where a VOR approach was available to runway 22 and an ILS approach was available to runway 04. Five minutes later, the aircraft was established on the VOR approach to runway 22 and still working Tanjung Pinang APP but when the controller advised that there was a tailwind of 14 knots gusting to 30 knots, the approach was discontinued at around 1,600 feet agl. Repositioning for an ILS approach to runway 04 was requested and received and once ‘runway in sight’ was reported, APP was advised and the flight was instructed to transfer to Nadim TWR (the Batam Airport ATC frequency) but contact with TWR was not attempted. The Captain disengaged the AP as the aircraft passed 1,195 feet agl and began attempting to position the aircraft manually to capture the ILS LOC and GS. The Nadim TWR controller then called Tanjung Pinang APP to advise that they had not received a call from the aircraft and did not have it in sight because of heavy rain. Having captured both LOC and GS, albeit from a recorded 15° intercept angle at less than 2 nm from the threshold, the Captain then re-engaged the AP at a recorded 668 feet agl to enable automatic tracking and autoland. However, this action was followed by a PFD ‘NO AUTOLAND’ annunciation which came as a surprise and he then failed to follow the ILS LOC and GS guidance manually. Having then belatedly noticed that both these indications had reached full deflection, he had disengaged the AP again and commenced a manual go around from 132 feet agl and informed Tanjung Pinang APP accordingly (Nadim TWR had already done so having briefly gained visual contact with the aircraft).

Whilst repositioning the aircraft visually for another attempt to land on runway 04, the Captain requested updated surface wind information which, having been obtained by telephone from Nadim TWR, was given as 340°/7 knots with visibility in the 04 direction of 500 metres and in the runway 22 direction of 6,000 metres. The Captain advised that “the aircraft did not have sufficient fuel to be repositioned for Runway 22 and that his next landing attempt on runway 04 had to be successful”. As this manoeuvre was being made (in IMC), the APP controller advised that the runway 04 visibility had improved slightly to 800 metres and that the flight crew “had the discretion to continue the approach”. 

Over the next couple of minutes, Tanjung Pinang APP and Nadim TWR controllers coordinated to ensure that the runway was kept clear and the APP controller continued to relay information between the flight and the Nadim TWR controller including a landing clearance. According to the Captain’s account, when the flight exited cloud on this third approach, the aircraft had been above the glideslope and offset to the left of the extended runway centreline and when he increased the rate of descent in an attempt to position the aircraft onto the glideslope whilst flying to the right to regain the centreline, an EGPWS Mode 1 ‘SINK RATE - PULL UP’ Warning had been annunciated as the recorded rate of descent exceeded 1,400 fpm. Another go-around was initiated when just over 200 feet agl.

The Captain, aware that “the remaining fuel quantity had reached critically low level”, advised the APP controller that they were going around and would perform a teardrop turn to re-position the aircraft low level for a visual landing on Runway 22 and this was accomplished. The aircraft was directed to a parking position and the passengers were kept on board whilst the aircraft was refuelled to await a subsequent positioning flight to Singapore operated by the same crew which was then completed without further event.

Discussion

(1) The relevant aircraft operator procedures in the OM, which had not been properly followed, were noted to require that:

• The PIC shall request delay information from ATC when unanticipated circumstances may result in landing at the destination airport with less than the FRF plus any fuel required to proceed to an alternate airport or the fuel required to operate to an isolated airport. 
• When the maximum delay or an Estimated Approach Time (EAT) is known, the flight may continue to hold, as long as landing at destination is assured and the fuel remaining at touchdown is not less than the FRF.
• The PIC shall advise ATC of a minimum fuel state by declaring “minimum fuel” when, having committed to land at a specific airport, the pilot calculates that any change to the existing clearance to that airport may result in landing with less than FRF. 
• The declaration of “minimum fuel” informs ATC that all planned airport options have been reduced to a specific airport of intended landing and any changes to the existing clearance may result in landing with less than FRF. This is not an emergency situation but an indication that an emergency situation is possible should any additional delay occur.  
• The PIC shall declare a situation of fuel emergency by broadcasting “MAYDAY, MAYDAY, MAYDAY, fuel” when the calculated usable fuel predicted to be available upon landing at the nearest airports where a safe landing can be made is less than the FRF.

The uncertainty about the duration of the weather-related delay at the intended destination was not adequately factored into the Captain’s decision to continue holding. It was noted that three other flights presented with similar information by ATC “were able to make a decision to divert earlier”. The crew also failed to monitor the south easterly movement of the convective weather from overhead Singapore towards Batam which meant that the delay diverting resulted in deteriorating weather at the previously selected diversion airport.

It was also found during Investigation interviews that the flight crew “had expected the air traffic controllers to have accorded priority for their flight after they had first indicated their fuel situation and provided a direct route when they made the decision to divert”. It was also considered that when ATC gave a heading which took the aircraft further from both Singapore and Batam whilst clearance to divert was awaited, a more assertive response would have been likely to have led to a more direct route to position the flight for a runway 22 approach at Batam.
 
(2) In respect of the activation of the ‘NO AUTOLAND’ annunciation which had not been anticipated by the Captain and had unsettled him, FDR data showed that the AP had been re-engaged just as the aircraft crossed the centre of the localiser beam and because this occurred less than 2 nm from the runway threshold, the aircraft had passed beyond the localiser beam before it began to turn to regain it. The Autopilot Flight Director System (AFDS) had identified the increasing localiser deviation and triggered the “NO AUTOLAND” message to alert that the aircraft track was not aligned with the runway centreline and that autoland could therefore not be engaged.

The operator’s FCOM stated that an autoland should not be attempted unless the localiser final approach course is aligned with the runway centreline unless CAT II or III ILS procedures are facilitated. Although some of the approach charts available to the operator’s pilots did contain an explicit statement to the effect that because of such a discrepancy, an autoland should not be attempted, others, including the one for the runway 04 ILS at Batam, did not. In this case, pilots must compare the charted procedure Final Approach Track (FAT) (041°) and the charted runway centreline (042°) to recognise that an autoland should not be attempted which in the high workload short diversion to Batam was not done.

(3) The consequences of the above led to a high crew workload during the diversion and resulted in both a number of significant mistakes and in poor tactical decision making despite the ultimately successful outcome.

The Conclusions of the Investigation were, in summary, as follows:

• The flight crew appeared to have prioritised a landing at Singapore Airport over a diversion to Batam where the weather was good. They had offered to perform an additional hold and an orbit whilst awaiting an opportunity to make an approach at Singapore despite having initially informed the controller that they could only perform a single hold after which they would be down to minimum fuel. 
• The weather at Batam only began to deteriorate shortly after the decision to divert there had been made. 
• The flight crew did not recognise that because the Batam runway 04 ILS Final Approach Track (FAT) was slightly offset from the runway 04 extended centreline, the option of an autoland was not available. This fact was not included in the operator’s Batam airport briefing despite the fact that such information was found to have been provided in the operator’s briefing documents for other airports where applicable. 
• The appearance of a PFD ‘NO AUTOLAND’ message during the first approach to runway 04 surprised the PF Captain who although initially continuing eventually decided to go-around even though by then the runway was in sight. It was considered that this message and the low fuel situation had intensified crew workload since they had they did not notice that they had not checked in with TWR and that no landing clearance had been given.

Safety Action taken as a result of this event by Singapore Airlines was noted as having included the following:

• A one-off training session for all its pilots covering the safety issues which had been highlighted by the event including: 
  • Appropriate use of the TEM model in respect of weather conditions and automation. 
  • The importance of effective communication with ATC. 
  • Reiterating the fact that compliance with SOPs is essential if operational safety is to be maintained. 
  • The need for pilots to be able to recognise high workload situations and their implications for decision making.
• The creation of a microlearning module within its EBT programme focusing on in-flight fuel management, diversions to alternate airports and declaration of low fuel state and the use of this event as a scenario during LOFT in the simulator to support appropriate application of the company’s fuel policy. 
• The contents of all the airport briefing documents have been reviewed to ensure consistency in the level of detail provided. It has been decided that information on whether an autoland is permitted should be removed in furtherance of this aim with pilots reminded to established by reference to the applicable approach chart to see if the FAT is offset or not.
• In conjunction with the Singapore ANSP has begun to examine whether the process of coordination with nearby alternate airports can be improved and whether the use of a dedicated team for real time operations management during adverse weather would be beneficial.

The Final Report was published on 25 September 2023. After noting action taken by both Singapore Airlines and the Singapore ANSP whilst the Investigation was in progress, it was determined that no Safety Recommendations were necessary.

Related Articles

• Fuel - Diversion to Weather Alternate
• Fuel - Flight Planning Definitions
• Fuel Management
• Fuel - In-Flight Management (Normal Operations)
• Automatic Flight
• Autoland
• Decision Making
• Missed Approach
• Surprise
• Threat and Error Management (TEM)