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Overcoming Resistance to (Oil) Change
BY PETER TAYLOR
The Need for Change In the pursuit of greater fuel efficiency, the newest turbine engines operate at ever-higher temperatures. The challenge for TEO suppliers has been to develop and deliver oils for these engines that can perform at elevated operating temperatures without breaking down to produce hard carbon particles (coke). Coke can block oil lines and, in the worst case, may have caused in-flight engine shutdowns.
“Engine development has continued relentlessly since the 1980s. One of the main challenges has been to overcome the tendency for oils to form coke,” Dowse says. “To resolve these issues, HTS oils, such as AeroShell Turbine Oil 560 (ASTO 560), were developed that have an extra margin of thermal stability for coking resistance. HPC oils offer low coking with improved elastomer seal compatibility and load-carrying capacity, which makes them particularly well-suited for use in the latest generation of high-bypass-ratio engines.”
Do They Pay? I
n a conservative industry, where safety is paramount, aircraft operators may be inclined to stick with what they know. Is this the same industry that is a model for the rigorous development, testing and implementation of numerous incremental changes that continually move it forward? Glass cockpits were introduced to reduce pilots’ workload for
increased safety; composite airframe and engine components have been adopted to reduce weight and deliver efficiency gains; and alternative fuels have been approved to reduce aircraft emissions. There are many examples that prove that change, if managed properly, does not have to imply risk and could bring significant benefits. So why, when the benefits of changing over to a modern turbine engine oil (TEO) can be demonstrated and reliable changeover procedures are proven and well documented, are so many aircraft operators reluctant to make the change? “You would not use 1960s-technology engine oils in a new
car,” says David Dowse, global technical manager, Shell Aviation, “but many airlines continue to use oils that were developed nearly 50 years ago in modern turbine engines that cost several million US dollars each. High-thermal-stability (HTS) TEOs were introduced over 25 years, yet not every airline or maintenance repair and overhaul organization (MRO) that could be taking advantage of their maintenance-saving benefits is doing so. The same is true of the latest high-performance-capability (HPC) oils, which have been introduced in recent years to give the highest levels of protection to the hotter-running modern jet engines. There is, perhaps, a perception that TEO changeover is
difficult or carries an unacceptable risk, but this may not be the case. Many airlines have changed oils using the top-up method preferred by most engine manufacturers without experiencing any issues, Dowse says. “We have just completed a year-long in-service evaluation
with Brazil’s TAM Airlines to examine the effects of changing to AeroShell Ascender, which is Shell’s flagship HPC oil,” he continues. “The changeover was made in two IAE V2500 engines on two Airbus A319 aircraft flying between São Paulo and Rio de Janeiro, one of the most demanding cycle-to-hour ratio environments. We regularly examined oil samples and TAM Airlines monitored engine parameters such as oil pressure and found no issues.”
64 Aviation Maintenance |
avmain-mag.com | August / September 2012
The main claim made for HTS oils is that they help to reduce maintenance costs, chiefly by eliminating some of the cleaning and component-replacement costs associated with coking. But how does this work in the real world? “Operators are sensitive about releasing this kind of information,” says Dowse, “but we can discuss the theory. The use of standard oils in the IAE V2500 engine has, under certain operational conditions, led to problems in the No. 5 bearing compartment from coking of the oil feed and scavenge lines. Failure of the No. 5 bearing compartment through insufficient lubrication or blocked scavenge pipes could cause excessive oil pressure or oil consumption; an oil fire or smoke in the tailpipe; or, in the worst-case scenario, in-flight shutdown. “Apart from the obvious safety issues, all of these could add significant maintenance and repair costs for damaged components. For example, Airbus A320 aircraft fitted with IAE V2500 engines require routine inspection of the engines’ No. 5 bearings and cleaning of the oil service tubes. By changing from a standard oil to a HTS oil, an operator of Airbus A320s could expect fewer engines to require parts during routine maintenance,” adds Dowse.
Reduced product misapplication risk Reducing maintenance costs is not the whole picture. Some airlines and MROs are electing to use a single HTS oil across mixed fleets to simplify operations and remove the risk of incorrect product application. This is possible, as these oils are approved for use in many older engines. Although these older engines do not require the latest TEOs, using a single product in all of a company’s engines simplifies inventories and removes the risk of mistakenly using an unsuitable oil in a more-modern engine. If, in future, manufacturers produce engines that can run only with HPC oils, operators with these and older engines in their fleet will need to decide whether to use two TEOs or to upgrade and use just one modern-technology oil.
Debunking changeover myths Airlines and MROs are sometime reluctant to change from one oil to another, perhaps perceiving changeover to be difficult or risky. This has some basis in fact: changes to an oil system that has reached a state of equilibrium can cause operational problems
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