Singapore Airlines SQ321: Weather radar likely failed silently before deadly turbulence, report finds

Summary

Singapore’s Transport Safety Investigation Bureau has released its final report on the May 21, 2024 turbulence disaster aboard Singapore Airlines flight SQ321, concluding that a weather radar underpainting fault on the Boeing 777-300 (registration 9V-SWM) “cannot be ruled out” as a contributing factor. One passenger died and 51 sustained serious injuries when the aircraft entered severe turbulence over Myanmar with no cockpit warning — on a radar display that investigators now believe was failing silently, without triggering any fault alert to the flight crew.

The TSIB stopped short of formally attributing the accident to the radar fault, but the finding materially changes the safety narrative around the incident. A fleet-wide review of approximately 29,000 Boeing 777 flights identified 32 separate radar under-detection or no-detection events across the type.

A final accident report has delivered the most significant finding yet in the investigation into aviation’s deadliest turbulence event in recent memory. Singapore’s Transport Safety Investigation Bureau concluded that the cockpit weather radar aboard Singapore Airlines flight SQ321 was probably not displaying weather data correctly — and that the crew had no way of knowing.

The aircraft, a Boeing 777-300ER operating the London Heathrow–Singapore Changi route, entered a region of severe turbulence over Myanmar on May 21, 2024, with no warning visible on the radar screen. Seventeen seconds after the seatbelt sign was activated, the turbulence became violent enough to momentarily trigger the aircraft’s stall warning system. Pilots took manual control to stabilize the jet.

The human cost was severe. Of 211 passengers on board, 51 sustained serious injuries and 22 sustained minor injuries. Five of the 15 cabin crew were seriously hurt. British passenger Geoff Kitchen, 73, died after suffering a cardiac event during the event. The aircraft made an emergency diversion to Bangkok, where ambulances met the flight on the tarmac.

The TSIB’s final report identifies a specific display fault — known as “underpainting” — in which the radar’s color-coded weather pattern failed to render correctly on the cockpit screen. Critically, the radar system had no mechanism to alert pilots to this failure in real time. Previous reports of underpainting on this specific aircraft had been logged before the accident, a detail investigators weighed heavily in reaching their conclusion.

What the final report actually found

The TSIB’s conclusion is carefully worded but unambiguous in its direction: radar underpainting or no-painting “without fault messages in the cockpit cannot be ruled out.” That phrasing reflects the limits of physical evidence — components from the weather radar system were sent to the United States for examination and testing — but it also reflects the weight of circumstantial evidence pointing toward a display failure the crew could not detect or correct.

Weather radar is designed to detect rainfall and render it in a color-coded pattern on the cockpit display. It is one of several tools pilots use to assess turbulence risk, and while it cannot detect all turbulence types — clear-air turbulence, in particular, remains largely invisible to radar — it remains a critical layer of situational awareness on long-haul routes through convective weather regions. The crew of SQ321 had been briefed on potential turbulence before departure from London but saw nothing of concern on their display as they flew over Myanmar.

Investigators have called on Boeing to develop guidance enabling pilots to identify whether their weather radar display is underpainting, and for maintenance engineers to detect these faults during ground checks. Neither capability currently exists in standard form.

The TSIB’s final report framing also prompted the bureau to issue a direct plea to passengers: always wear seatbelts when seated, regardless of whether the seatbelt sign is illuminated.

Why a silent radar fault changes the safety calculus

The most troubling element of the TSIB’s finding is not that the radar may have failed — it’s that it failed without any indication to the crew. Modern aircraft are engineered around the principle of alerting pilots to system degradation. A radar that displays a plausible but incorrect picture, with no fault code and no warning, represents a qualitatively different failure mode than one that simply goes dark.

That distinction matters for the broader industry. The TSIB’s fleet-wide review found 32 radar under-detection or no-detection events across approximately 29,000 Boeing 777 flights examined — a rate low enough to be statistically rare but high enough to demand a systematic fix. The investigators’ call for Boeing to develop pilot-facing diagnostic guidance is, in effect, an acknowledgment that the current design leaves a gap.

Air Traveler Club’s detailed analysis of the radar under-detection findings provides additional context on the TSIB’s fleet review methodology and what the 32-event figure means for 777 operations globally.

For Singapore Airlines specifically, the reputational stakes are significant. The carrier has moved quickly since the incident — real-time turbulence data on pilot iPads, stricter belt-sign service protocols, mandatory PA announcements — and those measures reflect genuine operational learning. But the final report’s radar finding introduces a maintenance and design question that no airline can resolve unilaterally. That now sits with Boeing and, ultimately, aviation regulators.

What the TSIB timeline means for 777 radar operations

This is an awareness story with a long regulatory tail. The TSIB has issued its final report and made specific recommendations to Boeing — but recommendations do not carry the force of airworthiness directives. The next meaningful development will be Boeing’s formal response to the radar diagnostic guidance request, followed by any action from the FAA or the Civil Aviation Authority of Singapore.

If Boeing’s engineering review identifies a design-level fix — rather than a maintenance inspection protocol — expect the FAA to issue an Airworthiness Directive covering the broader Boeing 777 fleet, potentially within 12 to 18 months of the recommendation being formally accepted. If the fix is procedural rather than hardware-based, the timeline compresses but the scope narrows to operator guidance rather than mandatory modification.

Watch for Singapore Airlines’ next operational circular on turbulence procedures. If the airline expands its belt-sign meal restrictions or introduces new radar-check protocols before departure, it signals that the final report is already reshaping frontline operations — not just closing an investigation file.

FAQ