SINGAPORE: Investigators have raised concerns about possible weather radar display issues on Singapore Airlines (SIA) flight SQ321 before it flew into severe turbulence over Myanmar in May 2024, leaving one passenger dead and dozens injured.
The inclement weather that caused the turbulence may not have been captured by the aircraft's in-flight weather radar, according to the full investigation report released by the Singapore Transport Safety Investigation Bureau (TSIB) on Tuesday (May 19).
The flight crew said they observed that the flight path was clear and that the weather radar showed no dangerous weather.
Investigators found the crew's account credible, noting that the same radar had under-detected weather on three occasions in the month before the incident, and that pilots did not discuss weather conditions in the lead-up to the turbulence – consistent with what would be expected had the radar shown nothing alarming.
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The weather radar manufacturer, which was not named in the report, said it found no evidence that the radar had failed to accurately detect and display weather during the flight.
The Boeing 777 was cruising at 37,000ft near southwest Myanmar on May 21, 2024, when severe turbulence struck as cabin crew were serving breakfast. Passengers not wearing seatbelts were flung to the ceiling.
Of the 229 people on board, 79 passengers and crew members were injured, some severely, including head and spinal wounds. A 73-year-old British man died. The plane made an emergency landing in Bangkok.
Preliminary investigations found that rapid changes in gravitational force and an altitude drop likely caused the injuries.
In June 2024, SIA apologised and said it would offer monetary compensation to the 211 passengers on board. Last year, components of the weather radar system were sent to the United States for examination.
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When the aircraft was around 300km from the incident location, the flight crew said the weather appeared clear, both visually and on instruments. From the cockpit, they could see some clouds in the distance but observed the immediate flight path to be clear.
Satellite imagery showed widespread cloud coverage over southwest Myanmar at the time, though the height of the clouds could not be determined from the images.
Four other aircraft flying in the vicinity also saw widespread clouds and deviated from their planned routes to avoid the weather. All four used a different weather radar system from SQ321, and were not flying at SQ321's cruising altitude of 37,000ft nor on the same flight path.
The investigation team said it was "unable to understand why the flight crew of the occurrence flight did not see the widespread clouds".
Photos from the ferry flight from Bangkok to Singapore showing one of SQ321's weather radars (right) under-detecting weather conditions. (Photo: SIA)
Investigators found that the radar could have been "under-painting" or "no-painting" – under-detecting or not detecting inclement weather altogether.
A review of SIA's Boeing 777 fleet maintenance records across around 29,000 flights found 12 cases of weather under-detection and 20 cases where weather was not detected at all.
Among these, two cases of under-detected weather were recorded on SQ321 on Apr 29 and May 1, 2024, and a third – where weather went entirely undetected – was logged on May 15, six days before the incident.
In all three cases, pilots reported no fault messages on the displays, and post-flight tests found no faults. The issue was not escalated to the manufacturer because SIA's procedures then required escalation only when the same defect occurred on the same aircraft three times within 10 days – a threshold the three reports did not meet.
Further evidence emerged after the incident, when pilots ferrying SQ321 from Bangkok back to Singapore on May 26 found that one of the radars was under-detecting weather.
"The investigation team opines that, taking into consideration the maintenance records, the ferry flight crew's observation of under-painting does suggest an issue of under-painting of the weather radar system," the report said.
The manufacturer conducted tests on SQ321's radar in various conditions, including different temperatures and in-flight, and found no evidence that the system had failed to accurately detect and display weather during the incident flight.
Investigators nonetheless concluded that the flight crew's account was credible. Had inclement weather shown up on the flight displays, it was "likely" the crew would have discussed it, but no such discussion was captured by the cockpit voice recorder.
After the turbulence, the pilot-in-command expressed surprise that he had not seen any dangerous weather on the navigation displays.
10:47 Min
Early findings into the extreme turbulence on Singapore Airlines flight SQ321 have been released. It showed that quick and sudden uncommanded altitude changes likely caused injuries. There were also rapid changes to gravitational or G-forces. Nadirah Zaidi explains what is a G-force, and what passengers might have felt during the turbulence. Also, independent aviation analyst Alvin Lie shares more about the interim findings and what’s next for investigators.
TSIB recommended that Boeing develop guidance for flight crews to identify and respond to under-painting or no-painting within a flight, and provide equivalent guidance for maintenance personnel.
The weather radar manufacturer was recommended to develop a means of recording weather display images to aid fault diagnosis.
A recommendation was also made to the International Civil Aviation Organization for larger aircraft built before 2023 to be retrofitted with systems that more reliably record flight data and cockpit audio after accidents.
Recipients of the recommendations must respond within 90 days, stating whether they accept each recommendation and, if so, when implementation will occur. Those declining must explain why.
The report noted that following the incident, SIA has taken several safety actions.
It has enhanced its turbulence monitoring tools on electronic tablets provided to flight crew, including an application to detect, predict and help avoid turbulence during flights.
It informed flight crews of potential radar under-painting or no-painting issues and provided guidance on how to manage them, and began sending reports of such issues on its Boeing 777 fleet to Boeing and the radar manufacturer.
Flight crews have also received refresher training on managing turbulence, and in-flight procedures, such as additional reminders for passengers to fasten their seatbelts, have been strengthened.
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The inclement weather that caused the turbulence may not have been captured by the aircraft's in-flight weather radar, according to the full investigation report released by the Singapore Transport Safety Investigation Bureau (TSIB) on Tuesday (May 19).
The flight crew said they observed that the flight path was clear and that the weather radar showed no dangerous weather.
Investigators found the crew's account credible, noting that the same radar had under-detected weather on three occasions in the month before the incident, and that pilots did not discuss weather conditions in the lead-up to the turbulence – consistent with what would be expected had the radar shown nothing alarming.
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Show More Show Less
The weather radar manufacturer, which was not named in the report, said it found no evidence that the radar had failed to accurately detect and display weather during the flight.
What happened on SQ321?
The Boeing 777 was cruising at 37,000ft near southwest Myanmar on May 21, 2024, when severe turbulence struck as cabin crew were serving breakfast. Passengers not wearing seatbelts were flung to the ceiling.
Of the 229 people on board, 79 passengers and crew members were injured, some severely, including head and spinal wounds. A 73-year-old British man died. The plane made an emergency landing in Bangkok.
Preliminary investigations found that rapid changes in gravitational force and an altitude drop likely caused the injuries.
In June 2024, SIA apologised and said it would offer monetary compensation to the 211 passengers on board. Last year, components of the weather radar system were sent to the United States for examination.
Collapse Expand
Related:
WHAT THE FLIGHT CREW OBSERVED
When the aircraft was around 300km from the incident location, the flight crew said the weather appeared clear, both visually and on instruments. From the cockpit, they could see some clouds in the distance but observed the immediate flight path to be clear.
Satellite imagery showed widespread cloud coverage over southwest Myanmar at the time, though the height of the clouds could not be determined from the images.
Four other aircraft flying in the vicinity also saw widespread clouds and deviated from their planned routes to avoid the weather. All four used a different weather radar system from SQ321, and were not flying at SQ321's cruising altitude of 37,000ft nor on the same flight path.
The investigation team said it was "unable to understand why the flight crew of the occurrence flight did not see the widespread clouds".
Photos from the ferry flight from Bangkok to Singapore showing one of SQ321's weather radars (right) under-detecting weather conditions. (Photo: SIA)
POSSIBLE WEATHER RADAR ISSUES
Investigators found that the radar could have been "under-painting" or "no-painting" – under-detecting or not detecting inclement weather altogether.
A review of SIA's Boeing 777 fleet maintenance records across around 29,000 flights found 12 cases of weather under-detection and 20 cases where weather was not detected at all.
Among these, two cases of under-detected weather were recorded on SQ321 on Apr 29 and May 1, 2024, and a third – where weather went entirely undetected – was logged on May 15, six days before the incident.
In all three cases, pilots reported no fault messages on the displays, and post-flight tests found no faults. The issue was not escalated to the manufacturer because SIA's procedures then required escalation only when the same defect occurred on the same aircraft three times within 10 days – a threshold the three reports did not meet.
Further evidence emerged after the incident, when pilots ferrying SQ321 from Bangkok back to Singapore on May 26 found that one of the radars was under-detecting weather.
"The investigation team opines that, taking into consideration the maintenance records, the ferry flight crew's observation of under-painting does suggest an issue of under-painting of the weather radar system," the report said.
The manufacturer conducted tests on SQ321's radar in various conditions, including different temperatures and in-flight, and found no evidence that the system had failed to accurately detect and display weather during the incident flight.
Investigators nonetheless concluded that the flight crew's account was credible. Had inclement weather shown up on the flight displays, it was "likely" the crew would have discussed it, but no such discussion was captured by the cockpit voice recorder.
After the turbulence, the pilot-in-command expressed surprise that he had not seen any dangerous weather on the navigation displays.
10:47 Min
Early findings into the extreme turbulence on Singapore Airlines flight SQ321 have been released. It showed that quick and sudden uncommanded altitude changes likely caused injuries. There were also rapid changes to gravitational or G-forces. Nadirah Zaidi explains what is a G-force, and what passengers might have felt during the turbulence. Also, independent aviation analyst Alvin Lie shares more about the interim findings and what’s next for investigators.
SAFETY RECOMMENDATIONS
TSIB recommended that Boeing develop guidance for flight crews to identify and respond to under-painting or no-painting within a flight, and provide equivalent guidance for maintenance personnel.
The weather radar manufacturer was recommended to develop a means of recording weather display images to aid fault diagnosis.
A recommendation was also made to the International Civil Aviation Organization for larger aircraft built before 2023 to be retrofitted with systems that more reliably record flight data and cockpit audio after accidents.
Recipients of the recommendations must respond within 90 days, stating whether they accept each recommendation and, if so, when implementation will occur. Those declining must explain why.
The report noted that following the incident, SIA has taken several safety actions.
It has enhanced its turbulence monitoring tools on electronic tablets provided to flight crew, including an application to detect, predict and help avoid turbulence during flights.
It informed flight crews of potential radar under-painting or no-painting issues and provided guidance on how to manage them, and began sending reports of such issues on its Boeing 777 fleet to Boeing and the radar manufacturer.
Flight crews have also received refresher training on managing turbulence, and in-flight procedures, such as additional reminders for passengers to fasten their seatbelts, have been strengthened.
Related:
Continue reading...