Printed headline: Lean Bill of Health
Aircraft and engine health-monitoring solutions are at the heart of predictive maintenance and the “on-condition” maintenance model. Knowing when a part is likely to fail, or when degradation in its performance will affect the life of another component, allows engineers to perform corrective actions that avoid costlier and time-consuming work later on.
Although predictive maintenance is a relatively modern trend, to some extent health monitoring always has been performed, for instance, with quick visual checks at a gate or more detailed borescope inspections in the hangar. However, big advances in the gathering and analysis of sensor data have transformed the practice, allowing many more operating parameters to be assessed and giving support teams the ability to check live inflight data.
Because engine work comprises the most significant chunk of maintenance spending, it represents the cutting edge of health-monitoring technology. Another reason is that an engine’s performance is the main contributor to one of an airline’s biggest expenses: fuel.
Accordingly, engine OEMs and certain MRO providers have been developing engine health-monitoring solutions for some time, but aircraft OEMs now are racing to catch up as they recognize the power of data to drive their growing aftermarket revenues.
“Boeing’s data scientists, analytics professionals and Boeing’s own engineering-services teams are partnering to develop more algorithms and the technology platforms that effectively handle big data of all varieties as the world of technology evolves,” says Dawen Nozdryn-Plotnicki, the company’s director of advanced analytics for digital aviation and analytics.
AIRCRAFT HEALTH MONITORING
Boeing and Airbus offer aircraft health monitoring for their customers via Boeing’s Airplane Health Management (AHM) and Airbus’ Airman.
Airman users can access real-time information and recommendations via a web portal for Airbus aircraft equipped with an onboard maintenance system and air-to-ground communications such as the aircraft communications addressing and reporting system or air traffic services unit. The core module of “Airman-web” monitors aircraft events, including systems, while an optional module connects to the maintenance information system and allows aircraft data requests.
Unsurprisingly, newer aircraft incorporate better technology that offers a wider range of data and interactivity. The Airbus A350 and A380 have the Aircraft Condition and Monitoring System (ACMS), which collects and records parameters upon detection of trigger conditions.
“With these collected parameters, it generates ACMS reports—the basis of the aircraft-monitoring function—which allow users to get advance indications of initial-stage system failures and to support system performance trending,” says Norman Baker, Airbus senior vice president for digital solutions.
Boeing’s AHM data also is accessible via the internet. Now part of the Boeing AnalytX Self-Service Analytics portal, the data is available on a cloud-based, scalable infrastructure. And like Airbus, Boeing is building more early-warning systems into its latest aircraft.
“Boeing integrates predictive maintenance expertise into the systems design process, ensuring new aircraft types have predictive maintenance concepts designed in, increasing the use of data analytics onboard the airplanes over the next few years,” says Nozdryn-Plotnicki.
Another use for the data, which overlaps with predictive maintenance, is to create optimal maintenance programs. Rather than conduct heavy checks strictly according to the standard maintenance planning document, airlines can use service-history data to create a workscope that better fits their needs and allows for more efficient shop visits and better-timed heavy-check intervals.
One benefit of such optimization occurs when an unexpected fault is found during a heavy check and there is no part in stock to rectify it. To avoid such delays, data analytics lets maintenance planners predict when certain faults or damage are likely to be found, so parts can be ordered in advance.
“Data analytics methods are already being applied by sifting through historic data on the tasks done during previous checks,” says Nozdryn-Plotnicki. “Armed with this information, maintenance planners can more accurately model and compensate for uncertainty, resulting in lower costs and decreased operational risk.”
ENGINE HEALTH MONITORING
Aviation Week predicts engine maintenance costs will account for roughly one-third of all aftermarket costs over the next decade. Thus it is clear that engine health-monitoring solutions, already well advanced at the OEM and MRO levels, will play increasingly important roles in maintenance planning.
To keep expenses down and operations running as smoothly as possible, health monitoring has three key goals: to maximize engine time on wing, to use mobile support when possible and, if removal and disassembly are required, to minimize the depth of intervention during a shop visit.
In the 1990s, Rolls-Royce started working data-based predictive maintenance into its TotalCare support packages. Since then, the amount of engine data transmitted before and after each flight has rocketed from kilobytes to terabytes, while machine learning and artificial intelligence have allowed new ways of analyzing it. As a result, the OEM says its health-monitoring solutions now affect 70% of an airline’s direct operating costs, up from 4% when they were introduced. This is because health monitoring now improves aircraft availability and efficiency rather than just reducing engine maintenance costs.
“Our latest EHM [engine health-monitoring] systems can reach parts we haven’t reached before and deliver much greater detail on request,” explains Axel Voege, Rolls’ head of digital operations for Germany. “We can now monitor line-replaceable units, such as variable-stator vane actuators and sensors—small parts but still crucial to making sure our engines are ready and available for flight—and predict when they need replacement rather than respond to their failure.”
Although OEMs such as Rolls continuously expand their health-monitoring capabilities, MRO provider Lufthansa Technik believes there are limitations to the interpretation of data provided by the manufacturers’ systems. Often, Lufthansa Technik notes, this is because alert rules are not customized to the peculiarities and specifics of an operator’s fleet. As a result, after following overhauls to OEMs’ recommendations, post-overhaul engine performance can fall short of targets, with big differences even among engines of the same build and vintage.
To solve this, Lufthansa Technik developed its own health-monitoring tool and created models that adapted general thermodynamic equations to specific engine data actually recorded in the test cell. The next step was to create a “digital twin” of an engine by scanning and measuring all its constituent parts and feeding the results into a computer. OEMs also have pursued the digital-twin concept, but Lufthansa Technik says its health-modeling tool goes further by evaluating a larger data set.
The engine control unit, for example, transmits status bits that signal the condition of different subsystems such as those that measure exhaust gas temperatures. In the event of an error in the measurement section, this is a critical piece of information. Usually, these status bits remain unused even though they are available in the raw data, but Lufthansa Technik’s tool accounts for them and can generate alerts on that basis.
“In recent years, there have been a number of examples where damage could have been prevented—damage that was undetected by the engine condition-monitoring system used at that time,” reports Christian Werner-Spatz, project manager for innovation and research projects in the engine services division of Lufthansa Technik.
The reach and utility of health monitoring clearly will continue to grow and in several different directions. Smaller, more robust sensors should allow “plug-and-play” solutions where operators can choose to slot new sensor types into their engines with minimal fuss. There will be more interaction with onboard units, so support teams can remotely request specific parameters both in flight and on the ground. And new software and algorithms will be used in analyzing more data and combining it in different ways to improve forecasting ability.
The potential for combining different data inputs is enormous, with Rolls already providing an example on the A350’s Trent XWB. As with other engines, turbine gas-temperature (TGT) readings are a common impetus for servicing. However, humidity also plays a role and can make an engine appear to need maintenance earlier than is necessary. Using coding apps within the Microsoft Azure cloud (Rolls collaborates with Microsoft to improve the former’s digital services), the OEM’s health-monitoring technology can access humidity data for every airport served by the Trent XWB and adjust for the effect on TGT readings.
“This means we can plan the number of cycles our Trent XWB engines can fly on wing more accurately, increasing their availability to customers. We are already looking at ways to support other Trent fleets on a similar basis,” says Richard Goodhead, Rolls senior vice president for civil aerospace marketing.
In 2019, Airbus plans to release Skywise Health Monitoring, which will be designed to leverage the big data collected through Airbus’ Skywise open data platform to help airlines manage unscheduled maintenance more efficiently. Detailed information about the new service is sparse, but Airbus says it will facilitate rapid troubleshooting and offer additional functions such as prioritizing corrective actions.
Looking further ahead, the next generation of aircraft may incorporate structural sensors to warn of impending damage or weakness in wings and fuselages. OEMs already use a variety of such sensors in testing and research and have proved the viability of embedding strain gauges into materials such as carbon fiber.
Airbus points out durability and reliability are critical when it comes to structural sensors. “New-generation sensors are coming on the market which could replace traditional non-destructive inspection equipment used for specific maintenance tasks, and Airbus is continuously evaluating possible use cases on both metallic and composite structures,” adds Baker.