Monday, August 1, 2005
Trend Monitoring is about Peace of Mind
Trend monitoring goes by many names: engine monitoring, engine health monitoring, engine condition trend monitoring, health and usage monitoring, predictive maintenance, and others. Defined as using engine operational data to find symptoms of damage, deterioration, or excessive wear, trend monitoring has been around in some form since the mid-1970s. New hardware technology that captures more engine data points and sophisticated software that finds more subtle trends--and thus finds potential problems sooner--are making trend monitoring even more valuable now than in decades past.
What does trend monitoring entail?
Trend monitoring consists of two basic components: engine data usually supplied by the OEM's engine control unit (ECU), and trend monitoring software or service supplied by the OEM or a third party. Nearly all turbine aircraft engines include an electronic ECU that adjusts fuel flow according to a set of parameters obtained from temperature and pressure probes and flow meters. Many of these parameters are recorded during certain engine events, such as engine startup and shutdown. The ECU also records additional parameters, such as the number of hours the engine has run, the number of start cycles, and any engine faults. Many ECUs allow this data to be downloaded into either OEM-provided software or to generic spreadsheets for later analysis.
Laboratory technicians and sophisticated software programs use the data taken from the ECU or aftermarket engine data collection units to measure increases or decreases in internal turbine temperature (ITT), N1 and N2 shaft rotational speeds, fuel flow, and other operational parameters against that engine's baseline. This determines the overall health of the engine and can point to component deterioration, foreign object damage, and excessive wear. If alarming trends are found, the operator can schedule an engine tear-down or overhaul at a convenient time instead of when components break. For instance, a rise in internal turbine temperature coupled with a decrease in N2 rotation speed may indicate damaged turbine blades or turbine guide vane torching. Without trend monitoring, many internal engine problems will not manifest themselves until a turbine blade is shed through the shroud or the engine shuts down.
Operators could obtain trend monitoring data through the ECU engine data, or by observing temperature and pressure gages in the cockpit and manually recording the data during each flight. However, to obtain a trend the operator would need to collect the data from a number of flights, plot the data in a spreadsheet, and then analyze the data. The amount of work involved with trending a fleet, coupled with the potential for saving substantial sums by catching small failures before they become inflight engine shutdowns, has led to a growth in the number of third-party trend monitoring programs.
Why use trend monitoring?
Many engine manufacturers require operators to furnish operational data on a regular basis to participate in warranty or maintenance programs. Honeywell's Maintenance Service Plan (MSP), for example, requires data uploaded to its website on a monthly basis. But this data is not only used to determine warranty coverage and schedule periodic maintenance. For Honeywell MSP customers, the data is also sent to Jet-Care International's American or European laboratories for trend monitoring as an integral part of the maintenance program on Honeywell HTF7000, TFE731, and ALF502/LF507 engines.
Jet-Care International (www.jet-care.com), based in Hampshire, England and New Jersey, U.S., is one of the largest independent trend monitoring companies in the world, currently monitoring the health of more than 12,000 engines in more than 90 countries. Its parent company, England-based Spectro, began providing oil, fuel, hydraulic fluid, and debris analysis services to aircraft operators in 1976 and founded Jet-Care in 1996 specifically to provide engine trend monitoring services for Honeywell and General Electric CF34 engines.
Honeywell customers download engine information from their engine control unit (HTF7000) or digital electronic engine control (DEEC on the TFE731). Under Jet Care's Gas Path Analysis (GPA) program, laboratory technicians analyze the data for damage or abnormal wear to engine components such as discs, blades, and stators not normally picked up in routine line inspections. The GPA program interprets outputs from thousands of engines that transmit key data from steady state cruise and takeoff. It can identify imminent blade failure, abnormal compressor/combustor deterioration, ingestion damage, and seal erosion, well before the components fail.
"Probably the most common problem [Jet-Care finds] is turbine rub, closely followed by bleed leaks and indication errors," said Jet-Care representative Martin Entwhistle, who provided several Jet-Care follow-up reports as research for this article. One TFE731-60 follow-up report indicated the ITT on the number three engine of a Falcon 900EX had risen by approximately 15 degrees Centigrade and N2 decreased by .5 percent during a three-month span. A tear-down revealed high pressure turbine (HPT) blade rub, coupled with a damaged shroud segment, damaged ITT harness, and eroded HPT nozzle segment.
"The estimated repair cost for this engine is in the order of $150,000," Entwhistle added to the report. "But if the parts had broken off and gone through the engine, the repair cost could easily have exceeded $300,000 to $450,000."
Additional potential economic savings arise from the prevention of in-service unscheduled removal. For both airlines and corporate operators, the economic impact of suddenly taking an aircraft out of service can sometimes overshadow the cost of the repair.
Who are the major players for your engine?
By virtue of its exclusive agreement with Honeywell, Jet-Care is the main trend monitoring service for TFE731 and HTF7000 engines. Jet-Care also provides trend monitoring services on the General Electric CF34 engine.
However, many other companies also provide third-party trend monitoring services. The Trend Group (www.turbinetrend.com), based in Clovis, California, uses a partner company's Equipment Condition Monitoring (eCM) software to provide trend monitoring services to Pratt & Whitney PT6 and PW100/300/500 engine operators, as well as monitoring for Honeywell TFE331, Rolls Royce AE3007, Williams FJ44, General Electric CJ610/710, and other engines. The eCM software, provided by SmartSignal (www.smartsignal.com), compiles an empirical model for the engine being monitored using actual sensor data, either current or historical, from normal operation. The Trend Group accepts the data in any format the customer provides, including mailed-in on postcards, e-mailed, faxed, or entered directly into The Trend Group's website.
After a period of time in which the normal operation data "trains" the software algorithms to create the baseline, the eCM software analyzes the newly downloaded engine data, comparing it against the empirical model to determine "very fine" differences in data. According to a SmartSignal white paper, the eCM software can save airlines an average of $8 per engine flight hour by predicting failure much earlier than other trend monitoring programs. The Trend Group analysts review the data and alert the customer of any potential problems. Customers can also view the compiled data and resulting trend graphs on their website.
Pratt & Whitney Canada also provides its own Engine Condition Trend Monitoring (ECTM) software as well as engine data hardware boxes for fixed-wing turbine, helicopter turbine, and PT6 turboprop engines through its wholly-owned subsidiary, Altair Avionics (www.altairavionics.com). The Microsoft-Windows based ECTM software allows operators and maintenance shops to do their own trend monitoring by downloading data directly from the Altair hardware to a laptop or personal computer.
Goodrich Aerospace (www.goodrich.com) provides its Health Usage and Monitoring System (HUMS) on Sikorsky military and civilian helicopters, including the UH-60 Blackhawk and its variants, and the S-92. In addition to the HUMS hardware, Goodrich provides a ground station software application that allows operators to download all engine data or "quick turn" downloads of only certain ground station data.
Standard Aero's (www.standardaero.com) TrendCheck engine monitor is a repackaged version of Altair's data collection hardware for the Pratt & Whitney PT6 turboprop. Used in conjunction with the P&W ECTM, TrendCheck automatically records engine trend samples, engine cycles, and operating hours during every flight.
When to start trend monitoring?
Engines with less than 100 hours since new or last major overhaul provide the most accurate baseline for trend monitoring because deterioration has usually not had a chance to occur. This is not to say, however, that older engines would not benefit from trend monitoring services. In fact, according to several trend monitoring companies, anytime is a good time to start trend monitoring.
"We had one customer who began trend monitoring about 70 hours prior to a scheduled overhaul because he wanted to see differences in performance," said Dale Taunton, director of operations for The Trend Group. "We started seeing signs of rapid deterioration after just 25 data points [flights] and alerted the customer, who decided to overhaul the engine with 40 hours remaining. Later, the customer's mechanic told him that the engine would not have made it to the scheduled overhaul."
Taunton said that trend monitoring is all about peace of mind. "We're not able to prevent the problem itself, but the idea with trend monitoring is to catch deterioration at the earliest possible time, analyze its cause, and fix the problem before it escalates."
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