Managing optimal engine performance is becoming increasingly critical, not only for safety and reliability, but for fuel burn savings so important to airlines and business jet operators. Advances in heat-resistant sensors and in full authority digital electronic controls (FADEC) and auto-throttles, along with improved onboard maintenance systems and Engine Indication and Crew Alerting System (EICAS) displays, are allowing collection, display and downloading of data for aircrews and technicians more rapidly and efficiently.
Major advances are being made in sensor elements — a critical component for both engine health monitoring systems (EHMS) and FADECs — that measure engine performance and transmit the responses. A current focus for sensors has been on improved reliability.
"A lot of the applications (on engines) are running much hotter than they previously had, so we are making sure the sensor elements have good temperature stability with time and they don’t degrade as quickly as previously," said Scott Wright, department staff engineer and technology leader for Unison Industries, a GE subsidiary based in Jacksonville, Fla.
To increase their capability, Unison is developing "intelligent sensors," which incorporate high-temperature electronics in the sensor itself. "They become an additional finger of the engine’s health," Wright said. "When (the airplane) is on the tarmac, and the technician is plugging in his wireless transceiver and saying, ‘OK, tell me your health,’ the system can inquire from the micro-control or data memory in our sensor and get a lot more information." But the greatest benefit from "smart sensors," according to Wright, is self-diagnosis — "when the sensor can report back to the EHMS and say, ‘I’m starting to see some degradation in my sensor element, and have stored that in my memory. I can tell you that I (the sensor) am going to be good for another month.’"
Wright feels that a better understanding of how sensors operate, drift and degrade is going to be the key to engine prognosis in the future.
"Prognosis is really where it’s at," he said. "You want to know that ‘I’m OK today, but I am starting to see the signs of early wear.’ And if we can crack this nut, there won’t be any engines that won’t start when all the passengers are on board."
To extend product life, Unison is providing improved insulation systems, using advanced coatings on sensor elements, and is using new interconnection techniques for small element wires. And the pressure is always on to make systems lighter. "The unsung hero of the industry is wire harnesses," Wright said. "Everyone wants to get the weight out of the harnesses."
Sensors monitor the physical parameters of temperature, pressure, engine speed and vibration and convert this into an electrical signal that goes to the FADEC or EHMS. And while most commercial engines have separate FADEC and EHMS boxes, the trend in military engines is to combine them, Wright said.
"This is where digital sensors can help," he added. "With a digital sensor, you are going to read that environmental parameter, and send it as a digital word to the FADEC. So the FADEC doesn’t have to process the signal any longer, it just reads the end result of what you have already processed inside your sensor."
The processing overhead the FADEC gains back by not having to process all these sensor signals, "gives you a chance to move the EHMS into the FADEC," Wright said. Driving this move toward consolidation is the fact that engines in development are getting smaller.
"There isn’t room to hang all these boxes on," Wright said, because of the tight constraints on some engines now. Unison is integrating its pressure and temperature sensors into a single housing, which it is offering for a new military engine.
The downsizing trend is particularly evident in business jet engines. Unison is the electrical component integrator on the GE Honda Aero Engines HF120 turbofan for the HondaJet and the Spectrum Aeronautical Freedom S-40 Very Light Jets (VLJs). Unison also has "Tier One" integration responsibilities, and provides the sensor suite, for GE Aviation’s new GEnx engine for the Boeing 787.
FADEC Advances
FADECs monitor and direct engine fuel flow and variable engine geometries, provide engine overspeed protection, and interface with the thrust reverser. Although provided earlier for military aircraft, the first FADEC systems on commercial airliners appeared in the late 1970s on the Boeing 757 and 767. Recent developments in FADECs have centered on providing diagnostic services for operators.
The FADEC 3 system will control the GEnx engine on the Boeing 787 and Airbus A350 XWB, and is currently in use on GE90-115B, CF6 and CFM56 engines. BAE Systems, a major FADEC supplier, provides these engine controls in a joint venture, called FADEC International, with partner Hispano-Suiza in France. (BAE acquired the former GE Aircraft Controls division in 2000.)
"In the latest variant, which we’ve done for GEnx, we’ve added additional monitoring signals whose purpose is primarily to support the maintenance, repair and overhaul (MRO) activity," said Dennis Slattery, director of Engine Controls for BAE Systems in Johnson City, N.Y. "This kind of diagnostic allows you to perform much better isolation of faults than in the past," and is part of an industry effort to move from scheduled maintenance to "a condition type of maintenance activity," he said.
The FADEC 3 control uses "a deterministic" Ethernet-based Avionics Full-Duplex Switched Ethernet (AFDX) communications bus replacing ARINC 429, allowing transmission at megahertz-type data rates, according to Slattery. The AFDX bus was first used on the Airbus A380.
"When we do our diagnostic work, we’ll transmit all information over the AFDX bus and that then feeds into the on-board maintenance system for further action," Slattery explained.
While fuel economy results primarily from performance of the turbine machinery, "certainly, having a box that has improved maintenance and improved diagnostics helps ensure that you are getting the performance you expected to have from the engine and the engine system," Slattery said. The engine performance information is also relayed by the data bus to the cockpit for display by the EICAS "and also interfaces into the flight system to make sure pilots have proper thrust settings," he added.
Computer advances are also improving FADECs. "With the ability and capability of the processors and memory today we can do much more modeling of the control system, get better sensor information and do better engine prognosis," Slattery said.
Increasingly, FADEC systems are being used on smaller aircraft, including business and regional jets, and even VLJs. "FADEC is basically ubiquitous now. Almost every system will have some level of FADEC," Slattery said. Although typically the smaller engines don’t have the sophistication or the variable geometry of the larger engines, their FADECs perform the same basic function.
Hamilton Sundstrand Engine & Control Systems in Windsor Locks, Conn., supplies FADECs and electronic systems and components to nearly every aero engine manufacturer for both commercial and military aircraft. The list includes Pratt & Whitney’s F-135 engine for the Joint Strike Fighter, the Rolls Royce Trent 900 for the Boeing 787 and the Airbus A380, and the GE T-700 engine for U.S. Army helicopters. The company will supply the FADEC for Pratt’s new geared turbofan (GTF) Purepower PW1000G engine, scheduled for delivery by 2013. P&W expects fuel burn to be reduced by 12 to 15 percent with the new engine, which will power the Bombardier CSeries and the Mitsubishi Regional Jet.
Hamilton Sundstrand eyes prognostics as the significant growth area in electronic controls, "because the FADEC really does know everything the engine is doing. It knows all the accelerations and decelerations, altitude conditions and surface conditions, and cycles. It’s just a matter of taking that data and using it in terms of where the engine has really been," said John Sullivan, vice president of engineering for Hamilton Sundstrand’s Engine & Control Systems unit.
Key factors driving new developments "are failure detection, both in engine and in aircraft, and in engine responses, and as processors get better and faster, smaller and less expensive, how to design your board so that you get the most out of them," Sullivan said. Sensor improvements are another key, he added. "But as the sensors get better, the box (FADEC and/or EHMS unit) has to improve as well, he said, citing 25 to 30 percent more input/output than previous generations, 50 percent less weight, 30 percent more electronic components and twice the capability in processing.
In the JSF program, one of Hamilton Sundstrand’s initiatives has been to combine the two boxes. "JSF is a significant step increase in the capability of electronic boxes — in monitoring and prognostics — technologies that can benefit the commercial side." Those technologies are supporting the new PurePower engine, Sullivan said.
In the smaller aircraft field, Hamilton Sundstrand provides engine controls for a number of Pratt & Whitney Canada engines, including the PW600, 500, 535 and 717, incorporating "significant technology improvements" for business jets, regional carriers and VLJs.
GE Aviation plays a central role in engine monitoring and control, both in designing and producing diagnostic systems and in supporting its customers by providing diagnostics and prognosis for GE engines in their fleets.
Along with its Operations group, GE Aviation’s Diagnostics Center provides services for 19,000 engines it monitors with some 300 operators worldwide. The company’s Standard diagnostic program, free to customers, includes customer notification reports (CNR) for all critical detected anomalies. The Comprehensive diagnostics plan includes the same service plus additional options.
"We’re looking at data, including cruise and takeoff, to determine the point where something might arise that could lead to maintenance or to service interruption," said Mike Fullington, Diagnostics and Prognosis Center technology leader for GE Aviation in Cincinnati.
"A big advantage is visibility into problems as they emerge. In prognosis, we’re looking for precursors. Our Operations group is in communications with airline maintenance people to determine if there is an urgent issue."
For its new GEnx engine, the company is providing a dedicated engine monitoring unit (EMU) tied in with the engine’s FADEC. "We’ve put our advanced capability into the dedicated EMU box and are getting new information, and a richer set of information from the sensors that we have," Fullington said.
The EMU focuses on gas path, vibration, fuel, start sequence and controls, isolating any damage that occurs to a compressor, turbine or combustor, and focuses on maintenance activities. The EMU box has processing capability, and "is actually creating our monitoring reports that will come through the aircraft’s data management unit (DMU) and will typically be downlinked via ACARS," Fullington said. These reports include cruise and takeoff data, as well as "start" and "post-flight" reports.
Fuel burn is a major concern, Fullington said. "In our basic diagnostic service, often if there is a problem developing with the engine it can lead to inefficiency in that engine. For example, if we have a turbine clearance control (TCC) valve that is inoperative, or a problem with variable bleed valves (VBV), that makes the engine less efficient and leads to increased fuel burn. We have had situations where we were able to isolate those problems, and by correcting them, you are restoring efficiency in the engine."
GE Aviation recognizes diagnosis and prognosis "as a key technology for our engines," Fullington said. "Our goal, ideally, is to provide information to the maintainer before there would be any impact to the flight crew. We would never have to provide any message to the flight crew because it has all been handled long before."
Avionics Contribution
Avionics OEMs contribute to engine monitoring and control with displays and other systems. For example, Rockwell Collins plays a supporting role through its EICAS display, which provides direct feedback to flight crews on how the engine is operating, and with its onboard maintenance systems.
The maintenance diagnostic computer (MDC) has been part of Rockwell Collins’ Pro Line 4 integrated avionics system since the early 1990s, and it is currently used on Bombardier CRJs and some business jets. A module inside the avionics cabinet, it collects information from the FADEC, stores it and downloads it for the operator.
The product has evolved into today’s Onboard Maintenance System (OMS) with more capabilities than the original MDC. As part of the latest Pro Line Fusion avionics system, instead of having dedicated hardware, it is a software application. Pro Line Fusion platforms will include the Bombardier C Series and Global family, Embraer Legacy 450 and 500, Cessna Citation Columbus and the Mitsubishi Regional Jet.
"We have increased the available memory and the exceedences — or instance temperatures exceeding allowed values — we capture," said Dave Wu, director of flight deck systems marketing for Rockwell Collins Business & Regional. "We take data at predefined points in an operating cycle and then the operator would look at these parameters and determine whether something abnormal was going on, whether any action is required."
The Rockwell Collins OMS allows the user to define the data capture parameters — the trigger points for data capture "that can potentially be used by airlines for FOQA (Flight Operations Quality Assurance), perhaps the most direct way we can contribute toward fuel reduction," Wu said. Some airlines are using these diagnostic tools to determine which particular engines are operating more fuel efficiently than others.
Rockwell Collins has provided its EICAS 4000 for business and regional jets, including the CRJ, and provides a version for larger commercial airlines. The CRJ has two displays dedicated to EICAS; the second display can be used for synoptic diagrams.
But with integrated systems like Pro Line Fusion, "we really don’t have a primary or secondary EICAS display. We really have a number of EICAS windows, and the crew can call up whichever window they want in several locations on the MFD," said Tim Rayl, Rockwell Collins senior director of business and regional marketing.
"Now we have MFDs with EICAS and other information," which can include pilot checklists, he said.
In stark contrast to the master caution and warning panels of 20 years ago, today’s warning of any abnormalities, currently text messages, are color-coded according to the severity level of the message — white, green, amber or red.
Autothrottle systems, which Rockwell Collins produces for the airline and business aircraft markets, also play an important role in engine control, although they are not generally thought of as part of the FADEC.
"What’s good about the autothrottle system, for example with Pro Line Fusion, is that it is fully integrated with the FMS (flight management system), the flight control system and, of course, the user interface, through the throttle quadrants," Rayl said. "And while that’s not exactly part of the engine controller, it certainly is a way the crew can talk to the engine controller. In addition to pilot workload reduction, I would say that more precise throttle positioning and easier synchronization are all benefits from an auto throttle system, and can also provide fuel savings."