The cloud point is the temperature at which wax crystals first appear in the fuel. As shown below, from a test device marketed by Indianapolis-based Polaris Laboratories, waxing can be sufficient to clog fuel lines:

Additives can lower the temperature at which waxing in fuel occurs, but testing and approval of a new additive could take as long as 5-10 years, according to a 2001 article titled “A New Look at Jet Fuel Additives” published by the Society of Automotive Engineers.  Extracts indicate that the problem of waxing, discussed in this publication is not trivial:

“There is seldom anything simple about aerospace. Whether it is design, engineering, manufacture, or operations, solutions to manifold challenges invariably have technological ‘side effects,’ which, in turn, bring new challenges. …

“So it was when consideration was given to the opening up of new commercial polar routes to provide more, efficient, and economical links between the continents of Europe, North America, and Asia. There would be potential for reduced flight times and increased payloads. But when specialists across the industry considered the potential technology challenges, one of the most important was the likely problem of jet fuel flow in ultra-cold ambient conditions at the typical cruising altitude and speed of aircraft such as the Boeing 777 and the Airbus 380.

“When it gets extremely cold, jet fuel can become waxy, just like diesel fuel, restricting flow to the engine. If this happens, options are limited to either descending to a lower, warmer altitude or increasing airspeed to enhance aerodynamic warming. Both options would increase fuel burn and reduce the benefits of polar routing.

“ ‘Rules for most aircraft state that action must be taken to warm the fuel if its temperature drops to within 3˚ C of the freeze point,’ [said} Mike Farmery, Technical and Quality Manager with Shell Aviation in the UK …

“[The] safety issue is critical. ‘The huge effort to gain all the necessary approvals has acted as a real block to the widespread application of additive technology in aviation fuel. However, this may be changing,’ said Farmery. He explained that the U.S. Air Force changed the game in the late 1990s with its initiative to find an additive to improve the thermal stability of jet fuels for the next generation of fighters. The successful result is the so-called ‘+100 additive,’ developed by BetzDearborn in the U.S. and marketed elsewhere by Shell Aviation as Air Performance Additive (APA) 101. …

“ ‘It has changed conventional thinking about the use of additives in jet fuel,’ said Farmery. ‘If we can improve thermal stability with an additive, why not the freeze point? There is a long history of cold flow improvers for diesel fuel. In principle, there is no reason why similar benefits could not be achieved in jet fuel … There is the potential for an aircraft taking standard Jet A at, say, Chicago, injecting an additive, and producing a fuel suitable for long-haul, polar flight, at a fraction of the cost of reformulating the base fuel.’ …

“Farmery said that in the short term, preventing fuel waxing in aircraft 35,000 ft above the North Pole will produce real economic benefits. Over the longer term, additive technology has the potential to bear much greater fruit. ‘In the automotive industry, engine and fuel developments have gone hand in hand, each one facilitating and stimulating the other,’ he said. … ‘The same benefits are promised to the aviation industry. Manufacturers are already looking at exploiting Shell’s APA 101 thermal stability additive to allow them to design engines that run hotter and are therefore more efficient.’ ” (http://www.sae.org/aeromag/techupdate/12-2001/)

An automatic jet fuel freezing point analyzer is now being marketed by PAC, an international manufacturing and service organization with advanced testing equipment for a wide variety of petrochemical, pharmaceutical and food/beverage applications. The company says it now offers an ultra-low temperature freezing point tester that’s about the size of a large briefcase:

“Long duration flight at high altitude subjects aircraft fuel tanks to very low temperatures, presenting the threat of fuel line and filter blockage due to hydrocarbon crystal formation. Heavy hydrocarbons and/or was-containing products can change a fuel’s cold behavior properties, creating significant flight safety risk. …

“Simply inject approximately 10 ml [0.33 ounces] of sample and press Test … The unit automatically controls test progress and delivers precise results in less than 15 minutes … The method, which is based on fundamental optical laws, detects all types of crystallization for any type of jet fuel.” (http://www.paclp.com/product/ISL/fzp5gs.htm)

Meanwhile, the General Electric Company, manufacturer of jet engines, filed a patent application in June 2004 for a jet fuel additive. Note in the extracted discussion below the concept of “knee temperature,” dealing with the sudden changes in fuel viscosity due to wax crystal formation. It would appear from this treatise that the problem of jet fuel and low temperatures during long-haul trans-polar flight is still being addressed. Extracts follow:

“The invention pertains to jet fuel blends and methods in which a cold flow enhancement agent is added to the jet fuel … It is known that fuel temperature decreases as flight time increases and that longer duration flights typically require lower freezing point fuels than do shorter duration flights. …

“Quite obviously, then, there is a need to provide freeze point depressant … which will allow for sufficient fuel flow to desired combustion locations at the extremely low fuel temperatures encountered at high altitude and long duration flights. …

“One such means of enhancing the cold flow properties of wax containing hydrocarbon fluids is via use of polymeric pour point depressant additives … These compounds act as wax crystal modifiers and/or anti-agglomeration agents to provide enhanced cold flow properties …

“The knee temperature is defined as the temperature at which a rapid viscosity increase occurs due to crystal formation. It is desirable to have the ‘knee temperature’ for a treated fuel to be shifted to a lower temperature relative to the neat fuel. It is also highly desirable to minimize the rate of viscosity increase as the fuel is cooled below the knee temperature … It can be seen from the data presented that the additives of the present invention lower the knee temperature of the fuel.” (http://www.wipo.int/pctdb/en/wo.jsp?wo=2005001005&IA=WO2005001005&DISPLAY=DEST)