SQ321’s weather radar may have failed to display true conditions before fatal turbulence, investigators find

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.