Business aviation could benefit from the use of more predictive maintenance. Airlines have seen using it for years.
MAINTENANCE
As the latest generation of business jets enter into service, their operators could reap the benefits of predictive maintenance—as the airlines have done for years.
Unlike preventative maintenance, which is time-based, predictive maintenance uses data generated by various component and system sensors that monitor the condition of the equipment at any given time to predict maintenance needs going forward. With that knowledge in hand, the operator can schedule maintenance well before a failure takes place and, in effect, turn a non-scheduled event into a scheduled maintenance task. “The mechanism of prediction comes into play with complex and interdependent aircraft systems with a high number of mechanical components and pneumatic connections,” explains Mia Witzig, head of digital solutions at Lufthansa Technik. “A time-based approach works out well for single components without bigger interdependencies when you have sensors reflecting their behavior. Whenever it gets more complex, that's the point where predictive algorithms help, and big data makes the difference.”
Lufthansa Technik uses predictive maintenance to reduce unscheduled maintenance and AOGs. Credit: Lufthansa Technik
Witzig notes that while predictive maintenance depends on the capability of aircraft to deliver the required data, acquiring it depends on recording intervals—not just the number of sensors on the aircraft. Many aircraft, she notes, send standard reports to the ground with “snapshot data” recorded from a specific sensor, in a certain flight phase. “That’s perfect for monitoring a specific component, but, if you want to recognize trends and derivations on more complex systems, you need a data series covering a complete flight phase or even the entire flight,” Witzig stresses. “With full flight data coming from the quick access recorder [QAR], for example, we can build a digital twin of the component within the digital twin of the aircraft and review the data with prediction models.” As a case in point, Witzig cites the Airbus A320’s bleed air system, which, she says, has generated “a significantly high number of operational incidents and pilot reports.” The system, she describes, is complex with a huge number of subcomponents, and a high number of possible failure modes--requiring a major troubleshooting effort. “Our EBASS [Engine Bleed System Suite] predictor monitors all the subsystems and sensors and brings the data back together in a digital model of the bleed system,” says Witzig. “This enables us to identify the root cause—data based—and decrease the no-fault-found [NFF] rate in the MRO shop significantly.” As a result, Lufthansa Technik’s A320 customers saw a 50% decrease in AOGs and a 30% reduction in engine removal rates.
Technicians service a HondaJet at Banyan Air Service in Fort Lauderdale. Credit: Banyan Air Service
Business Aviation Business aircraft operators are just starting to realize the benefits of predictive maintenance. “There are some systems on certain models of aircraft that are very good at predicting trouble points in engine performance and assist with the decision-making process of when to take a look inside the engine,” says Chris Bodine, vice president and general manager of StandardAero Business Aviation’s Augusta, Georgia, facility. “These systems are primarily looking at actual engine performance numbers and focused on changes in engine performance. They will track certain trends and provide alerts when there is a shift in performance.” Ron Grose, Falcon program manager and technical specialist (retired) at Duncan Aviation in Lincoln, Nebraska, reports that during the past 15 years, more recording/data collection equipment has been installed on business jets. Most of the data is collected from system components for quick troubleshooting of a component failure. At the same time, he points out that the data collection devices resident on the Falcon 900EX EASy, 2000EX EASy and the Falcon 7X/8X models represent “the beginning stage” of applying predictive maintenance to business jets. “The Falcon 7X and 8X are almost all-digital, with a considerable amount of data being monitored. The flight crew alerting system [CAS] messages, along with maintenance messages, are used to identify a system problem, the dispatch ability of the aircraft and for troubleshooting the system,” explains Grose, who continues to work for Duncan Aviation in a consultant role. Grose reports that for the newer generation of business jets, aircraft systems are being monitored by a digital flight data recorder (DFDR), a central maintenance computer (CMC)--or similar device—and an engine data collection unit. The data analysis is performed by the system OEM upon receiving it from the customer—under the OEM’s maintenance service plan. To illustrate, Grose says that, currently, the engine trend-monitoring data for the Falcon 2000EX EASy and 7X/8X is sent to an engineering group within Pratt & Whitney Canada for the PW308C and PW307A/D model engines. “That data can be downloaded to a laptop computer and sent to this group, or the aircraft can have a data transfer unit (DTU) installed to collect the engine parameters during flight and then download the data to this group using a cellphone service upon landing,” he explains. As an example, Grose sees the use of predictive maintenance for engine monitoring when, for instance, data analysis shows hot-section deterioration, causing performance issues. “Usually, the operator will receive an email or phone call from the engine manufacturer giving a specific time to get the aircraft into a maintenance shop.” Paul Rose, vice president of technical sales for Banyan Air Service in Fort Lauderdale, Florida, notes that the HondaJet HA-420 incorporates a system that can predict failures. The HondaJet’s Garmin G3000 integrated avionics suite, Rose explains, includes a CMC that collects system data and compares it to predefined operational events, failures and CAS messages, as well as data required for routine maintenance and troubleshooting. The data can be accessed locally by the technician via the CDUs (control display units) as an aid to troubleshooting or downloaded on an SD (secure digital) card and sent to HondaJet for a deeper analysis. In addition, the data can be transmitted to the ground via a maintenance data link with Wi-Fi capability using the Garmin GDL-59 data-link unit. “This central maintenance function also provides an engine trend-monitoring function in addition to monitoring other aircraft systems. This trend monitoring aids in the prediction of future system and component issues,” remarks Rose. In fact, a routine CMC download on a HondaJet revealed that an engine fuel delta P sensor was starting to show high resistance. “This was an indication that a failure of the delta P sensor was imminent,” says Rose. “HondaJet Field Service immediately contacted us, and we changed it out before it failed. A failure of this sensor would have caused an AOG.” According to Rose, the indication of high resistance on this sensor has HondaJet considering revising its inspection interval in the very near future.
—Paul Seidenman and David Spanovich are aviation journalists with more than 30 years of experience and are based in San Francisco.
