We often associate divert decisions with weather: if the weather isn't good enough to land, you divert to your alternate. In fact, a divert decision is almost always about fuel. If the weather is bad, you hang around until you don't have enough fuel to hang around any longer. The problem is that while you hang around, the weather or other conditions at your viable alternates can change. Sometimes the divert decision must come while you still have extra fuel.
— James Albright
Updated:
2024-12-15
9V-SWH, (Planespotters.net)
In Chapter 28, "A Practiced Calm," of Flight Lessons 1, I wrote about being in a formation of four tankers flying from an air refueling halfway across the North Atlantic. We handed off our fighters to a flight of England tankers and were returning to Maine without them, just us four tankers. While avoiding weather, our formation ended up heading 180, directly south and away from all land. As Number Four, our job was to follow. But once we got to our minimum fuel level, we broke formation and flew home. The formation leader was furious. Of the four aircraft, we were the only one to land on all four engines. One of the aircraft flamed out all four engines, losing the final engine right after touchdown at a divert base. It was a valuable lesson. Set a "bingo fuel" and stick to it. The crew of Singapore Airlines 319 could have used this lesson.
1
Accident report
- Date: 25 October 2022
- Time: 0820
- Type: Boeing 777-312ER
- Operator: Singapore Airlines
- Registration: 9V-SWH
- Fatalities: 0 of 280 persons on board
- Aircraft Fate: No damage
- Phase: Landing
- Airport: (Departure) London-Heathrow Airport (EGLL), England
- Airport: (Destination) Hang Nadim International Airport in Batam, Indonesia (Batam Airport)
2
Narrative
At 0801 hrs on 25 October 2022, while the aircraft was in the Kuala Lumpur Flight Information Region, Singapore Approach Control (SAC) informed the flight crew to expect to land on Runway 20R at Changi Airport. According to the flight crew, at that point, the flight management computer (FMC) indicated that their estimated fuel on landing was 7,000 kg, which was above the Final Reserve Fuel (FRF) requirement of 3,024 kg.
At 0805 hrs, SAC instructed the aircraft to hold over waypoint PASPU because of a tailwind on Runway 20R. A minute later, SAC informed all traffic on the Approach frequency to expect delay as the tailwind on Runway 20R was in excess of 10 kts. The PM indicated that, while in hold, the weather radar system on the aircraft showed that there was heavy precipitation over Changi Airport and the two alternate destination airports (Paya Lebar Air Base and Senai International Airport) and that the weather appeared fine over Hang Nadim International Airport in Batam, Indonesia (Batam Airport).
At 0810 hrs, SAC updated all traffic on the Approach frequency that the runway in Changi Airport to be used for landing had been changed to Runway 02L. Shortly after this, SAC informed the aircraft that the landing runway would be Runway 02L.
At 0822 hrs, the flight crew established contact with Singapore Arrival Control (hereinafter referred to as Arrival Control). Over the next six minutes, Arrival Control vectored the aircraft towards Runway 02L and informed the flight crew that there was heavy rain over Changi Airport and the visibility was reduced to 2 NM. During this period, the weather condition continued to deteriorate with the visibility reducing further to 500 m while the heavy rain persisted. By 0827 hrs, Singapore air traffic control services decided to hold off arrival traffic landing at Changi Airport, to assess the overall weather condition at that time.
At around 0829 hrs, Arrival Control informed all traffic on the Arrival frequency to expect a five-minute delay and that further updates on the weather situation over Changi Airport would be provided. The flight crew were instructed to proceed to waypoint SAMKO and hold. While en route to SAMKO, the flight crew obtained the Batam Airport Automatic Terminal Information Service (ATIS) which indicated clear weather in the vicinity of Batam Airport at that time, and informed Arrival Control at 0831 hrs that they could perform only one hold and would be down to emergency fuel. As the aircraft entered the hold at around 0833 hrs, Arrival Control updated all traffic on the Arrival frequency that the visibility for Runway 02L had deteriorated to less than 500 m.
Source: TIB/AAI/CAS.209, §1.1
A look at the weather system (see the charts below) shows their destination and all but one alternate where getting pelted with heavy rain. The lone good alternate, Batam, was south in the clear, but the weather was heading that way. It is unclear if the crew realized this, but they were aware fuel was getting tight when they said they could only perform one hold.
At 0836 hrs, as the aircraft was about to complete the first hold over SAMKO, the PM asked Arrival Control if there was any update to the situation. Upon being informed that there was no update, the PM informed Arrival Control that they were able to perform one more hold and that if they still could not have the clearance to commence approach to land at Changi Airport thereafter, they would need to divert to Batam Airport.
At around 0839 hrs and while the aircraft was in the first hold, the PM informed Arrival Control again that they could perform one more hold, as mentioned in their earlier communication. Arrival Control acknowledged the flight crew’s plan for a second hold and continued with its coordination with TPAC for the aircraft’s diversion to Batam Airport.
Source: TIB/AAI/CAS.209, §1.1
After deciding they could only perform one hold, they convinced themselves they could do one more. TPAC may have influenced the decision by saying that Batam had not yet approved the diversion. It seems Batam was not normally set up for a Boeing 777, but it was otherwise a suitable divert location.
At 0842 hrs, the flight crew informed Arrival Control that they were approaching SAMKO to complete their second hold. They were instructed by Arrival Control to fly heading 180°. The PM queried Arrival Control why the aircraft was being vectored in a direction away from both Changi and Batam Airports. Arrival Control explained to them that Changi Airport was still unable to accept arrivals and that TPAC had not yet approved the aircraft’s diversion to Batam Airport. The PM then offered to perform an orbit (instead of a third hold) over SAMKO, which Arrival Control approved.
Source: TIB/AAI/CAS.209, §1.1
By "orbit," I believe they meant a 360° turn, thereby squeezing a little more time into the delay, and keeping the aircraft closer to their destination, should the weather there improve.
At 0844 hrs, the PM informed Arrival Control that they needed to divert to Batam Airport. This was the fourth flight to make the decision to divert to alternate airport while three other flights had earlier elected to divert to alternate airports. At this point, the PIC, who had been the PM, took over as the PF while the First Officer, who had been the PF, became the PM. The flight crew made the decision to divert as there was no certainty that they could land at Changi Airport and as they assessed that the flight could divert to Batam Airport and land while complying with the FRF requirement. Arrival Control acknowledged the flight crew’s requirement for a diversion and instructed the flight crew to fly heading 180° so as to position the aircraft for landing on Runway 22 at Batam Airport.
Source: TIB/AAI/CAS.209, §1.1
The FRF is the Final Reserve Fuel requirement, which was 3,024 kg. The report didn't say what their fuel at this point was, but that 40 minutes earlier it was 7,000 kg. I've heard a 777 burns around 12,000 lbs per hour during the arrival phase, so call it around 6,000 kg/hour, conservatively.
I don't understand why the PIC decided to take over the PF role. They were in a situation where the decision making was key and I believe the lesser experienced FO would have been better used to fly the airplane while the PIC did the thinking. Sometimes, under stress, we like to fly the airplane because that makes us comfortable. But those are precisely the times we need to shoulder the uncomfortable task of decision making.
Ground track (from FlightRadar24)
A minute later, the PM queried Arrival Control again if Changi Airport was accepting arrivals. Arrival Control replied that that Changi Airport was still not accepting arrivals.
At 0846 hrs, Arrival Control informed the flight crew that approval for their diversion to Batam Airport was still pending. Arrival Control instructed the flight crew to fly heading 120° and thereafter 90°. At 0848 hrs, Arrival Control transferred the flight to SAC. SAC vectored the aircraft towards the boundary of its control area with the intention for the eventual hand-over of the aircraft to TPAC to occur at a position as close to Runway 22 of Batam Airport as possible. The PM informed SAC that they were down to minimum fuel. Two minutes later, SAC informed the flight crew that clearance from Batam Airport was still pending.
The PF declared “Mayday Fuel” at 0853 hrs when the estimated fuel on landing at Batam Airport was at the FRF. At that point, the aircraft was approximately 13 NM south-east of Batam Airport. SAC vectored the aircraft to an initial heading of 360° and instructed the crew to contact TPAC.
Source: TIB/AAI/CAS.209, §1.1
At the Final Reserve Fuel, they only had 3,024 kg.
By 0855 hrs, the flight crew had established contact with TPAC and were informed that they had priority for the landing. The PF was also performing communication duties while the PM was configuring the aircraft systems and providing information to the PF, in preparation for the landing at Batam Airport.
At around 0900 hrs as the aircraft was on the approach path for Runway 22, the flight crew were informed by TPAC that there was a tailwind of 14 kts gusting up to 30 kts. The PF opted to discontinue the approach at around 1,600 feet above ground level (AGL) and requested to reposition for another approach onto Runway 04.
Over the next few minutes, the PF manoeuvred the aircraft to avoid the weather and repositioned the aircraft with the intention to perform an autoland using the Instrument Landing System (ILS) on Runway 04. At around 0905 hrs, the PM informed TPAC that he had Runway 04 in sight. TPAC instructed the flight crew to contact Nadim Tower (the control tower at Batam Airport) on tower frequency of 118.7 MHz and the PM read back the frequency correctly.
Source: TIB/AAI/CAS.209, §1.1
With the runway in sight and fuel short, I would speculate that the PF was maneuvering to position the aircraft for a short final.
Shortly after the last communication with TPAC, the PF disengaged the autopilot system when the aircraft was 1,195 feet AGL. The PF recalled that he attempted to manually fly the aircraft to capture the glideslope and localiser signals with the intention to perform an autoland.
At around this time, the PF managed to position the aircraft on the localiser final approach course for Runway 04 and armed the autopilot Approach mode. The lateral and vertical mode of the aircraft’s autopilot flight director system managed to capture the localiser and glideslope mode respectively. The PF engaged the autopilot system when the aircraft was 668 feet AGL but was met with a “NO AUTOLAND” message on the Primary Flight Display (PFD). According to the PF, he was startled by the appearance of the “NO AUTOLAND” message and shortly after, he noticed that the localiser and glideslope deviation pointers were showing almost a full-scale deflection on his PFD, indicating that the aircraft was away from the centreline and glidepath of the runway. The PF disengaged the autopilot and, 20 seconds later, executed a go-around when the aircraft was 132 feet AGL.
Source: TIB/AAI/CAS.209, §1.1
At 1,195 feet AGL, they were probably inside of 3 nm to the runway and not on an extended final, hence the PF's need to manually fly to capture the glide slope and localizer and perform an autoland. The report makes a big deal about why the autoland wouldn't work: they were too low and the approach itself had a 1° offset and was not suitable for an autoland. I think the real issue here was maneuvering too close to the runway and being fixated on the automation.
At 0909 hrs, while the PF was repositioning the aircraft for another attempt to land on Runway 04, he requested TPAC for information on the tailwind at Runway 22. TPAC had to relay this request to Nadim Tower and was only able to reply to the flight crew 90 seconds later, informing that the visibility for Runway 04 and Runway 22 was 500 m and six kilometres respectively and that wind information was 340° at seven knots.
In response, the PF informed TPAC 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. At that point, the aircraft was approximately abeam the threshold of Runway 04 and the flight crew was about to commence a right turn for the final approach to Runway 04.
At about 0911 hrs, TPAC informed the flight crew that the visibility for Runway 04 was 800 m and that the flight crew had the discretion to continue the approach. The PF confirmed to TPAC that he would maintain his original intention to land on Runway 04.
Source: TIB/AAI/CAS.209, §1.1
Based on what happens next, I would again speculate that the pilot was maneuvering close to the runway in an attempt to get on the ground sooner.
According to the PF, when the aircraft broke cloud cover on the second approach to Runway 04, the aircraft was above the glidepath and offset to the left of the extended centreline of the runway. The PF increased the descent rate in an attempt to position the aircraft on the glidepath and extended centreline of the runway. However, the Ground Proximity Warning System (GPWS) generated a warning for excessive sink rate when the vertical speed exceeded -1,400 feet per minute. At 0914 hrs, the PF initiated another go-around in response to the GPWS warning, in line with the operator’s procedures, when the aircraft was at about 212 feet AGL.
Source: TIB/AAI/CAS.209, §1.1
I've read speculation from other sources that they were now down to about 1,000 kg, which seems about right.
At around 0915 hrs, the PF informed TPAC that they were going around and would perform a teardrop turn to reposition the aircraft to perform a visual landing on Runway 22. Subsequently, TPAC gave wind information as wind direction 330° at 15 kts to the flight crew. The PF was aware that the aircraft’s tailwind certification limit was 15 kts for landing and the operator’s procedure was not to land with a tailwind exceeding 10 kts. Considering that the remaining fuel quantity had reached critically low level, the PF decided to proceed with the approach to land on Runway 22.
The aircraft subsequently landed at Batam Airport and taxied to a parking bay. The aircraft touched down at Batam Airport at 0919 hrs with fuel remaining significantly below the FRF of 3,024 kg.
Source: TIB/AAI/CAS.209, §1.1
3
Analysis
Pilots
The captain was highly experienced, both in terms of total flying time as well as time in type. The first officer had a lot of time in type, but the report seems to have made a mistake either in his total time or time in type. Both pilots were proficient in terms of recent flight experience.
PIC: Total flying hours 14,371.5, Total hours on type 10,075.6, Flying in last 7 days 40 hr 10 min
FO: Total flying hours 2,261.9, Total hours on type 2,261.9, Flying in last 7 days 27 hr 40 min
Source: TIB/AAI/CAS.209, §1.4
Weather
Rain intensity over Changi and Batam Airports, TIB/AAI/CAS.209, figure 1
Changi Airport was affected by heavy rain during the period when the aircraft was vectored towards Runway 02L. During the period when the flight was holding over SAMKO, there was no rain over Batam Airport but the weather system was moving south from Singapore towards Batam.
The weather system moved south towards Batam Airport, located approximately 16 NM south-east of Changi Airport. Weather radar records showed that light rain was observed in the vicinity of Batam Airport at 0850 hrs. The rain continued to develop and intensify during the period when the flight diverted and made the landing attempts. When the flight crew declared “Mayday Fuel”, the weather condition over Batam Airport had deteriorated with a wider spread of moderate rain intensity.
By 0900 hrs, when the flight arrived for the first approach on Runway 22, there was moderate to heavy rain over Batam Airport. Over the next 20 minutes where the PIC attempted thrice to land the aircraft, the weather deteriorated with the rain intensity increasing and becoming more widespread.
Source: TIB/AAI/CAS.209, §1.6
Decision Making
The operator has indicated that there is no set policy or procedure for initiating a diversion and provides its flight crew with the discretion to initiate a diversion as required, as they are in the best position to evaluate the dynamic factors of each individual flight.
The operator’s fuel policy is clear in the guidance to its flight crew that if the maximum delay or an 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. However, the situation faced by the flight crew on the day of occurrence where information on the maximum delay or EAT was not available does not necessarily mean that a diversion should be initiated immediately.
In this occurrence, the flight crew appeared to have preferred to land at the scheduled arrival airport, Changi Airport, and held off deciding to divert based on the following decisions that were made: (a) They offered to perform another hold over SAMKO at 0839 hrs even though Arrival Control was unable to offer any update when queried by the PM earlier at 0836 hrs and they had previously indicated that they could only perform a single hold. (b) They indicated that they could perform an orbit at 0842 hrs, as they were about to complete the second hold, when informed by Arrival Control that Changi Airport was not accepting any arrivals and was in the midst of coordinating a diversion for the aircraft to Batam Airport. (c) They queried if Changi Airport was accepting arrivals at 0845 hrs despite declaring that they would divert a minute earlier and had accepted Arrival Control’s instruction to be vectored towards Batam Airport.
With the decision taken to stay in hold as much as possible in hope that the scheduled arrival airport starts to accept arrivals again, the trade-off for any flight crew is the reduced safety margins available to them when the decision to divert is eventually made and should they need to perform more than one landing attempt due to unforeseen events such encountering windshear during short finals that requires a go-around to be performed.
The investigation team is of the opinion that the repeated information on Changi Airport being unable to accept arrivals should be interpreted that a landing at the airport was not assured and the flight crew could have made a decision based on this information. Between 0820 - 0844 hrs, three other aircraft were presented with similar information by SAC and were able to make a decision to divert earlier.
Unfortunately, when the flight crew persisted with their decision to hold as long as possible, the weather system affecting Changi Airport started to move in the South Easterly direction towards Batam Airport. Had the flight crew initiated a diversion after the first hold based on their original intention as communicated to Arrival Control, when they were first instructed to hold over SAMKO, it is reasonable to believe that they would have arrived at Batam Airport earlier and would be able to attempt a successful landing on Runway 22 in a better weather condition.
Source: TIB/AAI/CAS.209, §2.1
4
Conclusions / Safety Actions
The report does not offer a "cause" but does include conclusions and safety actions.
Conclusions
The flight crew appeared to have given preference to land at Changi Airport over diverting to Batam Airport where the weather was good. The flight crew offered to perform an additional hold and an orbit despite informing SAC that they could only perform a single hold and would be down to minimum fuel. The weather over Batam Airport started to deteriorate shortly after the flight crew decided to divert.
Source: TIB/AAI/CAS.209, §3
Note: the report conclusions focus on the flight crew's attempts to engage the autoland system. I do not include these because, in my view, they are incidental to the primary cause of this incident.
Safety Actions
The operator reviewed the event and conducted sharing sessions with all its pilots covering the following:
- The appropriate application of the operator’s threat and error model in respect to this occurrence. The threats from the operating environment, weather and automation were reinforced.
- How the pilots can employ active communication to inform other parties of information in a timely manner and ensuring the message is understood by the receiver.
- Reiterating that compliance with the operator’s procedures is essential to maintain operational safety.
- How to recognise high workload situations and the associated human factors such as attentional tunnelling which could result in errors in decision making.
The operator has incorporated lessons learnt from this occurrence as a micro-learning module in its evident based training program focusing on inflight fuel management, diversions to alternate airports and declaration of low fuel state.
Source: TIB/AAI/CAS.209, §4
References
(Source material)
TIB/AAI/CAS.209, Final Report, B777-300ER (9V-SWH), Low on Final Reserve Fuel, 25 October 2022, Transport Safety Investigation Board, Ministry of Transport, Singapore, 25 September 2023.