SQ321 turbulence: Radar under-detection cannot be ruled out, says final report

Quick summary

Singapore’s Transport Safety Investigation Bureau released its final report on May 19, 2026, concluding that weather radar under-detection on Singapore Airlines flight SQ321 — a Boeing 777-300 operating from London Heathrow to Singapore Changi on May 21, 2024 — could not be ruled out as a contributing factor. One passenger died and 51 sustained serious injuries when the aircraft entered severe turbulence over Myanmar without cockpit warning. A review of approximately 29,000 Boeing 777 flights found 32 separate radar under-detection or no-detection events across the fleet.

The radar fault left no cockpit alert — pilots had no way of knowing the display was showing them an incomplete picture. Singapore Airlines has since suspended all cabin and meal service whenever the seatbelt sign is on.

The weather radar on the Boeing 777-300 that killed a British passenger and seriously injured 51 others over Myanmar was probably not showing pilots the full picture. That is the central finding of the Transport Safety Investigation Bureau‘s final report, released May 19, 2026, nearly two years after Singapore Airlines flight SQ321 dropped without warning on its overnight run from London to Singapore.

Investigators believe the radar display was “underpainting” — rendering weather data incompletely on screen while appearing to function normally. Critically, the system had no mechanism to flag the fault to the flight deck. The pilots saw clear skies. The radar said nothing was there. Seventeen seconds after the seatbelt sign came on, the turbulence became severe enough to activate a stall warning and throw unbelted passengers and crew into the cabin ceiling.

The aircraft involved, registration 9V-SWM, was 18 years old at the time. Maintenance records reviewed by investigators showed the underpainting problem had appeared on this specific airframe at least twice in the three weeks before the accident.

What the final report actually found

The TSIB’s fleet-wide review covered approximately 29,000 Boeing 777 flights and identified 12 cases of weather under-detection and 20 cases where weather was not detected at all. That is not a theoretical risk — it is a documented pattern across the type.

For the specific aircraft that operated SQ321, the record is more pointed. Under-detection events were logged on April 29 and May 1, 2024. A no-detection case followed on May 15, just six days before the incident. A post-incident test ferry flight on May 26, 2024 found one radar still under-detecting weather, which the report treats as corroborating evidence for the underpainting theory.

Investigators stopped short of declaring the radar fault the direct cause of the accident. The formal language — “cannot be ruled out” — is deliberate. It reflects the limits of what physical evidence can prove after the fact, not a lack of concern. The TSIB has called on Boeing to develop guidance for pilots to identify underpainting in real time, and for engineers to detect the fault during maintenance checks. Neither capability currently exists.

The full TSIB findings are detailed in Channel NewsAsia’s reporting on the final report, which confirms the radar review scope and the ferry-flight finding. Three passengers injured in the incident have also filed a personal injury claim at the UK High Court — the SQ321 turbulence litigation names Singapore Airlines as defendant and remains ongoing.

Why a radar that fails silently is a different kind of problem

Most aircraft system failures announce themselves. A hydraulic fault triggers a warning. An engine anomaly shows on EICAS. The underpainting fault on SQ321’s radar did none of that — it simply showed pilots a cleaner picture than reality warranted, with no indication anything was wrong.

That is what makes this finding significant beyond one flight. The TSIB’s fleet review found 32 radar anomaly events across roughly 29,000 Boeing 777 flights. Those events happened on aircraft that were otherwise considered airworthy, maintained to standard, and cleared for service. The fault was invisible to the crew and, apparently, to the maintenance process.

The closest industry parallel is the Qantas Flight 32 uncontained engine failure on November 4, 2010, which also originated from Singapore and triggered a global reassessment of engine inspection standards. That event reshaped powerplant oversight across the industry. The SQ321 final report is now doing something similar for weather radar integrity — forcing a question that had not been formally asked: how do you verify a sensor that fails without telling you it has failed?

Singapore Airlines has already moved. The carrier now suspends all meal and cabin service whenever the seatbelt sign is on, and both pilots and cabin crew are required to make PA announcements at sign activation. A new turbulence data tool on pilots’ iPads pulls live weather from on-board Wi-Fi rather than relying on pre-flight briefing data compiled hours earlier. These are not cosmetic changes.

Steps for Singapore Airlines passengers right now

The TSIB report confirms that turbulence can arrive without cockpit warning, even on well-maintained aircraft with functioning instruments — which means the seatbelt is the only reliable protection a passenger has.

• Keep your seatbelt fastened whenever seated. The TSIB investigation team explicitly called on passengers to wear seatbelts even when the sign is off. On SQ321, the sign came on just 17 seconds before severe turbulence hit. That is not enough time to react from a standing position in the aisle or galley.
• Do not wait for a PA announcement. Singapore Airlines now requires announcements at sign activation, but the gap between sign-on and severe turbulence can be shorter than the announcement itself. Treat the sign as your only warning.
• Expect service interruptions on long-haul sectors. Under the new policy, meal and cabin service stops the moment the seatbelt sign activates. On turbulence-prone routes — particularly sectors crossing the Bay of Bengal, Myanmar, and the Andaman Sea — this may happen multiple times during a flight.
• Check your aircraft type before booking. Singapore Airlines’ booking page shows operating equipment on most long-haul sectors. The Boeing 777-300ER is the primary type on LHR-SIN and comparable trunk routes. The radar review covered the broader 777 fleet; if this affects your comfort level, the information is available before purchase.
• For injury claims, check Montreal Convention eligibility. This is not an EU261 or UK261 compensation case — turbulence injuries fall under the Montreal Convention if carrier liability is established. Passengers departing Singapore are generally outside EU/UK261 scope. Legal advice specific to your departure point applies.

Watch: TSIB’s follow-on safety action items — expected after the final-report circulation window — will determine whether Singapore Airlines and maintenance providers must revise radar inspection procedures for long-haul 777s. If revised inspection steps are mandated, it signals the underpainting fault is being treated as a systemic airworthiness issue, not an isolated anomaly.

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