Sunday, October 1, 2006
Engine Oil Analysis: Used to Trigger Maintenance Action
Jet-Care specializes in the analysis of engine oil, hydraulic fluid, and fuel to alert operators to unusual amounts of contaminants.
Just as medical doctors use blood analysis to fathom the workings of the human body, modern technologists employ quantitative assessments of the constituents of engine oil to assess the health of the powerplants.
The analysis of engine oil, like medical testing, is performed at a laboratory specialized in the work. In this case, over 14,000 engines from some 4,000 operators in 82 countries send their engine oil to one of three Jet-Care laboratories -- two in Europe, trading as Spectro, and one in the U.S. The U.S. laboratory, visited recently by Aviation Maintenance, is located in New Jersey, a location picked for its proximity to three commercial and corporate airports. The company also tests fuel and hydraulic fluid for contaminants.
All three of the laboratories operate to the ISO 17025 quality standard and are UKAS (United Kingdom Accreditation Services) certified. This allows original equipment manufacturers (OEMs) like Airbus and Boeing to use Jet-Care's services without audit. Jet-Care holds approvals from most major engine manufacturers, including Allison Engines, Pratt & Whitney, Textron, Lycoming, Honeywell, Turbomeca and Williams International.
The routine tests of oil, and the debris captured by the filter, can indicate not only if an engine is running correctly, but also if an incipient problem needs to be addressed by maintenance action.
The testing runs anywhere from $40 to $300 per engine, per test. "For anybody on a power-by-the-hour program, the oil sampling costs pennies per hour," said Josh Wagner, a sales and marketing official for Jet-Care at the New Jersey facility.
In one case, the testing demonstrated to an operator that its switch from oil brand A to brand B was not effective, prompting a return to the use of brand A.
In another case, levels of titanium contamination in the oil showed that turbine shafts were wearing out. With timely maintenance action, the operator was able to save six shafts valued at $1.5 million. In the case of a reciprocating engine, premature wear of the piston rings was detected through analysis of the engine oil, again facilitating effective maintenance intervention. Examples of cost savings and cost avoidance through routine testing of engine oil are legion (see box page 26).
The testing can also tell what is not supposed to be in the engine. For example, a screw fell out of an overhead fixture in a hangar, into the oil that was then poured into the engine. Testing of the oil revealed trace elements of the material used to manufacture the screw, which was subsequently found and removed from the engine.
Basically, client companies or operators send engine oil samples and used oil filters to Jet-Care, usually by overnight package delivery, for analysis. The engine oil is sent in four ounce plastic bottles, and the filters are likewise dispatched in sealable plastic containers. The New Jersey laboratory receives these samples from throughout North America, Canada, Latin America, and from the Far East.
Samples are logged in, and testing is completed routinely the same day, usually within about two hours. Results are e-mailed to the customer immediately.
For the engine oil, the analysis is repeated three times to achieve consistent and accurate results. These tests are also performed against a control sample, again for accuracy. For the oil filters, they are ultrasonically cleaned in solvent, which frees up the entrapped debris, which is then dried and subject to analysis. Debris is classified by type, and an assessment is made of the approximate amount of each type.
The material is examined by scanning electron microscope, and it is checked against a database of all engines to help locate the origin of debris or wear. The course of further action is determined by what is found.
Among the things the laboratory technicians look for is evidence of change to oil additives and oil viscosity. Remember that one of the purposes of oil is to reduce friction between metal surfaces, thereby reducing temperature and heat buildup. Significant deviation from fresh oil data may indicate oxidation through overheating, the presence of a different grade of oil, or contamination, either by water or other fluids. One of the more significant tests on the oil is for the presence of metals, such as iron, aluminum, chromium, nickel, titanium, and so forth. The presence of titanium, for example, may be an indicator of wear if the amount is increasing over time as measured by parts per million (see box below).
Another test performed is the total acid number, or TAN. The TAN is a measure of an oil's degradation due to oxidation or overheating, which will manifest as an increase in the oil's acidity. Thus, the TAN is a useful indicator of the health of the lubrication system. Of interest, the rate of TAN increase can be more significant than its actual value, as acidity can rapidly increase, and with serious consequences for the engine. For example, a quart of hydraulic fluid mistakenly poured into the engine oil sump will show up readily in the TAN testing.
The oil analysis measures contaminants of eight microns of size or smaller. The filter analysis catches larger particles. "We correlate the weight of filter debris to what should be the expected value," said Wagner. For example, accumulating 50 milligrams of debris at 150 filter hours might well be normal. Accumulating the same amount in 10 hours use of the filter would not.
A major virtue of the Jet-Care approach is to assess the engine oil and contaminants over time, and against all other fleets of similar profile. The comparative reporting can take many forms. "For example, we can search by oil brand, or oil type, and we can see an entire fleet of engines after, say, 5,000 hours of operation," said Wagner. In actuality, the ways the data can be presented are almost limitless.
"We don't just produce a report," Wagner explained. "It's what we do with the data from the tests, over time, that is significant. We can compare one engine to the rest of the world, or all engines operating in, say, the New Orleans area, to the rest of the world."
"We can see sodium or magnesium increases, characteristic of offshore helicopter operations," said Wagner. The tests also show silica characteristic of operations in a desert/dusty environment.
In another case, alerts were generated about zinc in the oil submitted by one operator. "It turned out that they were storing the oil in galvanized drums," said Wagner. "We adjusted the limit for zinc so the customer wasn't alerted constantly."
However, in cases where the analysis turns up a potential problem for the customer, the "advanced warning" provided by the reports e-mailed promptly, are reinforced by a telephone call to the operator. "We don't just rely on e-mail," said Wagner.
The question of how often the tests should be performed varies. For instance, a major power plant manufacturer has oil and filter analyses scheduled at every 150 hours of engine operation. For corporate operators, flying some 300-400 hours per year, a sampling rate of once every 100 hours may be recommended. For scheduled airlines, once every 200 hours may be sufficient.
For helicopters, particularly the high-stress gearboxes, testing every 25 hours may be recommended.
The Virtue of Outsourcing
There are two reasons why engine oil testing is best done by an outside contractor like Jet-Care, as opposed to doing it in-house. First, the necessary equipment can be hugely expensive. The two scanning electron microscopes used at Jet-Care's New Jersey laboratory, each about the size of an office desk, cost about a quarter-million dollars apiece. "These are the equivalent of two houses sitting here," said Pam Kaur, Jet-Care's laboratory supervisor. Second, the people at Jet-Care acquire a certain expertise from analyzing thousands of oil samples. They know what metals, and in what proportion, can be expected in a normal oil sample, and they are quick to spot deviations. In short, the people are an invaluable resource.
The benefits of routine testing are there, but perhaps difficult to quantify with a standard cost-benefit equation, claims Peter Smith, head of technical services at the company's U.K. facility. "The oil testing might trigger a maintenance action that may cost $50,000 if the problem is caught in time, versus $1 million if it's not," he explained.
"That is essentially our problem in showing the cost-benefit," he confessed. However, the cost of a problem caught in its incipient stages can be considerably less expensive than if allowed to fester. A main location bearing, for example, repaired in time, is far less expensive than replacing the whole engine if the problem persists to the point of failure.
According to Jet-Care officials, the virtue of engine oil testing is best summarized thusly: We need to know what's going on with the engine, and the answer is available within hours of receipt of a sample.
The next frontier of engine oil testing may be the common use of trace materials in components like bearings in all engines. If the trace material shows up in the engine oil analysis, that would be used as a signal to replace the bearing.
As in the case of blood analysis for humans, sampling of oil for minute or trace amounts of contaminants, or markers, is leading -- with data analysis -- to insights regarding engine health. For executives managing the operation and maintenance of aircraft, the payoff can be longer hours of operation and lower-cost maintenance.
Success Stories From Routine Testing of Engine Oil
Regular oil analysis for a major airline detected a consistent increase in titanium levels from a Pratt & Whitney PW4060 turbofan engine. The engine was removed and a spinning seal plate in the No. 2 bearing area was found. The wear on the titanium shaft was within the repairable limit, and the engine replacement was performed on time. The operator saved an estimated $200,000 by not replacing the shaft.
Prior to departure, the chip detector light for the number 1 engine -- a PW4060 -- illuminated on a Dassault Falcon 2000. The chip detector was found to be heavily contaminated with debris. More than 5,000 shiny platelets of M50 (high-speed bearing material) were found when the debris was examined under Jet-Care's scanning electron microscope. Because of the chip detector design, it was known that the problem lay in the number 1, 2 or 3 bearing. From this analysis, it was determined that the engine could be repaired in house.