On May 23rd, Singapore Airlines Flight 836, an Airbus A330-343 flying from Singapore to Shanghai, was cruising through inclement weather at 39,000 feet with 188 passengers and 12 crew aboard. While over international waters, both Rolls-Royce Trent turbofan engines experienced a total loss of power.

This unusual and terrifying situation is often called a “dual flameout,” and is possibly the most undesirable malfunction to occur aboard a twin engine airliner. Fortunately, pilots are trained extensively to handle such emergencies and the Singapore Airlines crew reverted to their checklists and standard operational procedures in order to restore power.

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But even with their quick reaction, power wasn’t restored until the widebody jet dropped 13,000 feet… a long, silent descent into the unknown.

Fortunately, the loss of power was only temporary. Flight 836 landed safely in Shanghai as originally planned 100 minutes after the nearly catastrophic incident took place and remained on the ground for four hours while undergoing a comprehensive inspection. No anomalies were detected and the same aircraft then proceeded to fly the return route with only a two hour delay.

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So what happened here, exactly? Airliners utilize multiple engines for speed, power and safety. Having more than one engine provides redundancy for long range flights (especially those crossing an ocean or the Arctic), offering pilots options to keep the aircraft airborne in case of an emergency. The Airbus A330 is certified for ETOPS-180 (Extended-range Twin-engine Operational Performance Standards), or any route within 180 minutes from the nearest airport under single-engine power. To be able to fly so far under just one engine’s power is an incredible feat of engineering, and the Rolls-Royce Trent turbofan is one of the most reliable and advanced jet engines ever built. However, a pilot’s choices are greatly diminished if neither engine is making power simultaneously.

Peculiarly, this event occurred on a practically brand new aircraft (registration 9V-SSF), which first flew on March 12th 2015 and entered service with the Singapore fleet less than two months prior in April 2015. Singapore Airlines operates 30 Airbus A330’s, with two additional airframes on order and one in storage. This comprises nearly one third of their fleet, which also includes the Airbus A380 and Boeing 777.

The Rolls-Royce Trent 772B turbofan engine earned certification in 1997, produces 71,100 lbs of thrust and has never been associated with an incident or accident in which life was lost. One theory for this incident involving Flight 836 is that the weather system the aircraft was traveling through was to blame, causing microscopic ice crystals to develop on the engine’s fan blades which degrade efficiency and performance.

Operating under the assumption that high altitude ice crystals played some role in this event, the ice crystals would have melted as the aircraft descended to a lower altitude with a warmer temperature. This would have allowed pilots to restore full power and continue the flight normally. This is just one theory, and with such a complex machine there could be multiple culprits for such an incident. For instance, a recent Airbus A400M military transport plane also lost power supposedly due to a simple software glitch, resulting in a horrific crash. Another example is an incident that occurred in 2008, when a British Airways Boeing 777 experienced a dual engine flameout while on approach to London Heathrow. The widebody landed short of the runway due to lack of thrust, resulting in a total hull loss and 47 injuries. The Air Accidents Investigations Branch of the British government determined the cause to be a loss of flow in the aircraft’s fuel system as a result of ice buildup.

No injuries were reported on Flight 836, and firsthand accounts of the incident didn’t immediately appear across social media. This has lead some to speculate that passengers weren’t aware of the severity of the situation. While “loss of power to both engines” conjures chaotic images of oxygen masks deploying from overhead compartments, the cabin going pitch-dark and the aircraft rapidly losing altitude, in reality the engines were still windmilling and power to the aircraft’s critical systems (including cabin pressurization) would have been delivered via the auxiliary power unit (APU) or the aircraft’s Ram-Air Turbine (RAT).

The absence of the engine’s distinctive drone and the feeling of a shallow descent would have likely been the only indication inside the cabin that something was awry—seemingly a ghostly, unnatural, deafening silence to anyone accustomed to airliner travel. Yet the Trent turbofan is remarkably quiet in cruise to begin with, not to mention power changes and descents occur during flights normally, so the experience may have seemed odd only to those seasoned passengers that were paying close attention.

The airline and aircraft manufacturing industries have bet enormously on ETOPS-rated twin-engine reliability over the last few decades. Years ago, around the dawn of the jet airliner age, flying on three out of four jet engines was not an uncommon practice as the technology was nowhere near as reliable as today.

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Even so, with so much added complexity including dense software which was never a factor in aviation’s analog era, modern aircraft can suffer from seemingly mysterious circumstances even decades after they first entered service.

Investigators from Airbus, Rolls-Royce and Singapore’s Air Accident Investigation Bureau (SAAIB) continue to review the incident but have not named a cause.

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Photo credits: Top shot - Robert Frola/Wikicommons, Wing shot - Edwin Ieong/Wikicommons, Bottom shot - Edwin Ieong/Wikicommons

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