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Questions about the safety of SAP first emerged in 2010 when a passenger jet belonging to a major international airline experienced engine trouble, causing it to lose thrust control and land at twice the normal speed. Thanks to the skill and training of the aircrew, this resulted in no injuries. But the cause was a mystery. Though not involved with the fuelling of the flight, Shell Aviation was asked as an independent expert by an Aviation Regulator and the airline, to investigate the cause of the incident. The team found a possible correlation between the presence of SAP and issues with the fuel-control unit experienced during the flight.

Following a further sequence of incidents, the International Air Transport Association (IATA) convened a Special Interest Group in May 2014 to investigate whether SAP was a factor in these cases as well. Participants included representatives from airframe and engine manufacturers, fuel-filter manufacturers, airlines and airline associations, the Energy Institute, and Shell Aviation, which chaired the group.

Conventional fuel monitors are designed to capture water and solids from fuel before it's used by an aircraft. They do this by employing a physical filter to catch solid particles and SAP, a material that is also used in disposable diapers, to absorb water. As the IATA investigative taskforce looked into these fuel monitors, they discovered that under certain circumstances, SAP could become saturated and swollen and leak small, gel-like material into fuel. In rare cases, this SAP material can cause significant operational issues in engines. Since 2010, a total of eight incidents have been identified as a result of SAP migration into the fuel and have resulted in issues ranging from a loss of control to in-flight engine failure.³

"We started to see other engine and aircraft types involved, [issues like] heavy surge damage, complete turbine failure, an aircraft that lost its engine on take-off. So really serious stuff," Midgley said.

Filter monitor manufacturers have confirmed it is not possible to guarantee that no SAP will pass downstream in the fuel into the engines. ⁴And engine manufacturers will not endorse any level of SAP in fuel as "safe." The conclusion: It's not possible to use a filter monitor that contains SAP and be 100% confident that SAP contamination will not happen and will not impact engine performance.⁵

"We can see from that data that even with the controls that we have in place, existing filter monitors still have the potential to release superabsorbent polymer, Midgley said. "So, when we combine that with no known lower limits (for SAP in fuel), then we must transition away from filter monitors as an industry."

While the solution of replacing filter monitors is straightforward, it is not necessarily easy. Thousands of fuelling systems worldwide employ filter-monitor technology using SAP. The only currently available existing alternative involves the use of water filter separators, which are bulky and difficult to retrofit into existing fleets. Huge challenges loom at the world's largest and busiest airports, whose high-flow hydrant operations mean that new filter water separators would need to be massive and require new vehicles to carry them.⁶

"The filter water separator is physically a much, much bigger, much heavier vessel. That means that most vehicles don't have the space to fit them. If they do, you're often exceeding the weight limitations of the vehicle. So instead of now changing a filter … you're also changing the vessel. You're also potentially changing the vehicle as well. So that leads into a program of very high cost and very long implementation programs," Midgley said.

In addition to the potential safety risks, the price of postponing action to replace traditional filter monitors could be high. Inaction could impose costs on airlines since engine OEMs have determined that there is no safe level of SAP. Damage determined to be a result of SAP, therefore, may not be covered by OEMs.

"Real safety issues have been detected and need proper mitigation," Andreas Schmidt, Manager of Jet Fuel Quality at Lufthansa, told the webinar. "So, there is no safe option available besides phasing out filter monitors. We need to act now, and each play our role. Change can only happen if we all start acting."

The challenge of transitioning to safer, SAP-free refuelling demanded collaboration across the industry. With this in mind, Shell Aviation and FAUDI Aviation worked together to combine their technical expertise and develop a solution that doesn't use SAP. The result is a technically mature, drop-in solution that replaces the filter monitor with a dirt-defence filter which captures dirt suspended in fuel along with a new and extremely sensitive sensor that continually scans the fuel for water contamination. This system is 100% SAP-free and is called Shell Jet Protection.

The water sensor continually assesses fuel quality and can detect 30 parts per million of water in fuel flowing at up to ⁷ meters per second. When you're detecting less than 30 parts per million, then it's a very small number. "To put this into context, it is the equivalent of trying to detect and count 270 people in the 9-million-person population of Greater London if they were to all run past you at once. Then that's the sort of level of granularity we're talking about. So, these sensors are quite impressive technology." Midgley said.

If water is detected – a rare occurrence – fuelling of the aircraft is shut down. It detects the water rather than using a chemical to absorb it. The solution is pending approval by the Joint Inspection Group (JIG) and should be available later in 2020.⁷

"We're at the position now where we're confident that that technology is robust, and the industry as a whole has been working together with field trials to make sure that it operates successfully in the field," Midgley said. "Our intention is to have no filter monitors left in Shell locations where we are under operational control by the end of this year, end of 2020."

Safety is our industry's top priority, and the science is clear: Current filter monitor solutions emit SAP, and there is no safe level of SAP in aviation fuel. By recognising this risk and working together now, the industry can transition away from filter monitors that use SAP to enable safer and more efficient operations.

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