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related to the dislodging of coke already present and the swelling or shrinking of O-ring seals. Change by draining, flushing and refilling is thought to increase the chances of coke shedding and may alter the swelling characteristics of any rubber. However, many airlines have successfully changed oils without any issues, and detailed field trials, such as the one recently completed by Shell Aviation and TAM Airlines, demonstrate that, when carefully managed, the risks are minimal. All the major engine manufacturers, including Rolls-Royce, Pratt
& Whitney, GE Aviation, CFM and IAE, prefer changeover by the top-up method in which the new oil is added as required during normal service. Some additional monitoring may be required during the changeover period. This position is based on extensive in-service evaluations and laboratory testing, which show that the top-up method greatly reduces the chances of disturbing the equilibrium in the oil system. With this method, the old oil is replaced with the new oil at an exponential rate that depends on the in-service oil consumption rate. “Many operators and MROs are realizing the benefits of using HTS oils. For example, Cargolux and Orient Thai Airlines have recently benefited from converting to ASTO 560,” Dowse says. “Operators that are reluctant to upgrade could be missing out on the chance to reduce their maintenance costs. Since changing to ASTO 560, Thai Airlines has reported a reduction in engine bearing failures and oil coke deposits. This has helped it to extend the on-wing lifespan of the engines and resulted in reduced overhaul and maintenance costs.”
What’s Next for TEOs?
It seems likely that engine development will continue in the same direction, with higher operating temperatures being sought and longer intervals between scheduled maintenance. So, what does that mean for TEOs?
Dowse says, “At a recent Shell Aviation customer symposium, one original equipment manufacturer (OEM) speaker speculated that we could see ultra-efficient lubricant-free engines in the future. That sort of advance, if it happens, is some way off. Until then, improving TEO performance will be critical to achieving higher efficiency and the significant TEO breakthrough we have made will contribute to this. “Antioxidants improve an oil’s thermal stability to reduce coking. Some TEO manufacturers use antioxidants that can create elastomer compatibility issues such as degradation of the O-ring to the extent that it loses its sealing ability and causes oil leaks. For them, formulating the oil is about getting the best compromise between these two properties. “Our premium TEOs use a different antioxidant chemistry. This enables ASTO 560 and our latest TEO, AeroShell Ascender, to offer both coking control and elastomer compatibility. In fact, in the industry-standard elastomer test, fluorocarbon elastomers lasted almost twice as long with AeroShell Ascender than with other oils tested and the coke deposits were considerably reduced. It is also designed to cope comfortably with the longer intervals between scheduled maintenance that we are likely to see in the near future. “AeroShell Ascender is already fully approved for the IAE V2500 series engines that power the Airbus A320 family (A320, A321 and A319), the Airbus Corporate Jet and the McDonnell Douglas MD-90. OEM field trials are under way and further approvals are likely by the end of the year. “And, of course, our research and development work continues, and not just in TEOs. We have also made a significant breakthrough in developing a new wheel-bearing grease that will help the industry in its aspiration to triple the number of landings for each set of bearings. But I cannot talk about this until next year’s launch.” AM
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avmain-mag.com | August / September 2012 65
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