The formation of these potentially harmful carbon deposits requires airlines to regularly inspect, clean or replace critical lubrication system components, significantly adding to the line maintenance workload and risk to aircraft downtime.
To ensure HPC oils provide improved coking resistance, AS5780 requires HPC oils to be able to perform in two test rigs for twice the duration of SPC oils while producing half the amount of coke deposits. These rig tests are the U.S. Navy ERDCO Bearing Deposition test (FED STD 791 Method 3410) and the Hot Liquid Process Simulator (HLPS) SAE ARP5996 coking propensity test. Figure 3 shows the performance differentiation in the HLPS test.
To meet the HPC performance requirement, oils need to combine a thermally robust ester base stock with an optimized blend of performance additives. When designing lubricants, manufacturers will always look to exceed, rather than meet, the specification requirement to provide OEMs and airlines with confidence of extra thermal and oxidative protection.
By offering improved high temperature performance, today’s HPC lubricants are augmenting the on-wing life of the engine by reducing scheduled and, more significantly, unscheduled maintenance activity.
According to American Airlines repair/part development engineer, Dan Foust, commenting on the airline’s conversion to BP’s HPC lubricant 2197, the maintenance implications can be significant.
“Since introduction of BPTO 2197 oil into AA’s CF6-80C2 Boeing and Airbus fleets ... we have experience far less coking buildup in our turbofan engines,” Foust says.
“It has eliminated two field trips per year to replace excessively coked oil tubes. This has translated into better system reliability and reduced maintenance costs.”
Making the decision to convert
The decision to change to a higher performing oil involves both technical and economic considerations, and can sometimes instigate a divergence between engineering and procurement decision-makers. Often, the cheapest AS5780-approved oil is procured to secure immediate financial benefit, but at the risk of increasing scheduled and nonscheduled maintenance action and thus increased cost in the long-term.
The cost of fleet engine oils represents a comparatively small proportion of an airline’s operating costs, and can account for less than 0.01 percent of the annual operating cost for a twin-engine, single aisle, standard body commercial aircraft. In contrast, engine and aircraft maintenance represents a significant percentage of an airline’s annual operating costs. The implication of this is that, to obtain noteworthy cost savings, commercial airlines need to use oil that will support long-term engine performance and reduce maintenance costs both directly and indirectly.
Airline turbine oil procurement practices will differ depending on the airlines themselves as well as the financial climate that may exist at a particular time. In turn, the relevant drivers used by the key decision-makers may well change. Should turbine oil be purchased on a simple tender basis to derive the cheapest product or should it be viewed as a critical engine component requiring more strategic considerations? Air BP Lubricants has recognized that these two contrasting “engineering vs. procurement” viewpoints may exist within many commercial airlines and has developed a ‘value comparison tool’ to assist airline customers in their decision-making around oil procurement (see box on page 19 for more information).
Any decision to convert to a new turbine oil is generally made on the basis of technical benefits, and evaluated in terms of the financial implications during the later stages of the decision. The decision to convert to an HPC oil should be strategically influenced by both commercial and technical considerations during the planning phase. By determining the value of HPC oil to both the “operational health” of the fleet and to the business, decision-makers can ensure the long-term procurement goals of the airline whilst achieving improved performance for their fleet.
The milestone, which coincides with the oil’s 15th anniversary, effectively means that BPTO 2197 has lubricated engines travelling the equivalent distance of six million trips around the world.
Drawing on customers’ own operational data, the web-based ‘tool’ allows Air BP technical sales staff to calculate and show potential benefits.
Nesma Airlines' switch to Air BP Lubricants High Performance Capable (HPC) Turbine Oil 2197 (BPTO 2197) has resulted in better engine performance, reduced maintenance issues and notable cost savings.