Aircraft Health Monitoring (AHM) is the process of collecting and analyzing data from aircraft components and systems to assess their condition and identify potential problems. AHM can be used to prevent unplanned maintenance, improve operational efficiency, and enhance safety. In the rapidly evolving aerospace industry, the AHM market is a cornerstone of progress and safety. According to a research report by the research firm Research and Markets, the AHM industry is estimated at $4.7 billion in 2022 and is projected to nearly double to $9.7 billion by 2030.
“The end goal of aircraft health monitoring is to gain descriptive (what’s happening), predictive (what happens when we have challenges), and prescriptive (if we reduce fuel in the wings, what impact will it have on the wings themselves) analytics that can improve the safety and efficiency of an aircraft,” says Stephen Hall, director of research strategy and partnerships at SKYTRAC, Kelowna, British Columbia, Canada. “This level of data analysis can help identify causal factors contributing to aircraft distress or incident occurrences important for accident investigation and criminal agencies. In addition to the AHM, there are also tangential capabilities such as engine trend monitoring, flight data monitoring, operational loads monitoring, GADSS, and real-time Health and Usage Management Systems (HUMS) that can provide insights into that status of specific aspects of an aircraft.”
Daniil Ravvin, Senior Product Line Manager at Honeywell Aerospace, says AHM is becoming increasingly important in the aviation industry. “As aircraft become more complex and operate in more demanding environments, the need for AHM to ensure safety and reliability becomes more critical.”
Ravvin cites the following benefits of using AHM:
• Reduced maintenance costs: AHM can help reduce maintenance costs by identifying and preventing problems before they lead to failures.
• Increased operational efficiency: AHM can help to improve operational efficiency by optimizing the performance of aircraft systems.
• Enhanced safety: AHM can help to enhance safety by identifying and preventing potential hazards.
• Improved fleet management: AHM can help to improve fleet management by providing insights into the health of aircraft and their components.
The number of AHM products available on the market ranges from software-based options to dedicated integrated vehicle health management systems that can monitor dedicated gear, engines, and even the aircraft structural frame. Data acquisition modules, wireless sensors, and artificial intelligence (AI)/machine learning (ML) software can glean insights from gathered data.
Ravvin says dedicated software can monitor sensors based throughout the aircraft body, and some software-based solutions can monitor bus data and evaluate the real-time condition of that data. “[AHM products offer] a proactive approach to minimize accidents before they happen. Data signaling potential problems on one aircraft can be used to comprehensively analyze an entire fleet. Condition Based Monitoring (CBM) substantially cuts maintenance/operating costs in the near term and over the life cycle of the aircraft and avoids costs of spares usage, dedicated test flights, and asset recapitalization.”
Hall says one of the largest challenges to industry adoption of AHM products is that aircraft health monitoring recorders are not mandated for use; they are optional requirements for operators.
“A unique way to solve this challenge is to leverage Minimum Equipment List (MEL) approved devices. [This includes] SKYTRAC’s ADT-5000 Global Aeronautical Distress and Safety System (GADSS) solution that is designed to ingest aircraft health data to provide operators with real-time insights into any potential distress scenarios detected. Although GADSS was introduced for emergency scenarios, the data captured can be leveraged for complete AHM. With global, real-time satellite connectivity, this captured data can be transmitted directly from the aircraft to databases on the ground, or upon landing using more cost-effective Wi-Fi or cellular offloading to secure networks, which is also known as Timely Recovery of Flight Data (TRFD).”
Operators are constantly looking for ways to expand the number of aircraft components they can analyze with AHM. Many are trying to expand their aircraft condition(ing) monitoring systems (ACMS) capabilities inside their data acquisition and management units to capture more data from more components. “ACMS has access to thousands of parameters from many sensors or LRUs,” says Edgar Salvador, director of business development and technical sales, Teledyne Controls, El Segundo, California. “However, it only captures information for hundreds of parameters. In order to expand the number of parameters captured, operators rely on software tools that enable them to customize their ACMS and get the parameters they need. Teledyne works closely with its data acquisition and management unit customers, providing expertise, technologies and service solutions to enable them to extract more information from these systems. ACMS improvements allow airlines to gather more parameters, but airlines still need to worry about making that data available on the ground.”
Traditional AHM systems, according to Bobby Anderson, VP/GM of commercial aviation at Shift5, Rosslyn, Virginia, “can provide only a limited set of data about the aircraft and its condition. Shift5 is different. We capture all the data transiting onboard operational technology (OT) systems, not just a small subset. We then combine this onboard data set with other relevant information, like the stage of flight, weather information, and flight plan details, and analyze all of this data comprehensively for anomalies.”
Are there certain parts of the aircraft that need more aircraft health monitoring than others? Critical systems and structures such as undercarriage mechanisms and primary structures such as wings, which are candidates for barely visible impact damage (BVID) are important to monitor.
“It is crucial to understand the actual loads experienced by critical aircraft components to predict inspection, maintenance and/or component replacement intervals,” says Hall. “Critical component management can change, even for established aircraft over time or due to a change in roles (e.g. passenger aircraft to aerial firefighting). Overall, we need to ensure that changes in the spectrum of operational don’t result in unconservative inspection, maintenance or replacement intervals (e.g. acceleration of widespread fatigue damage (WFD) or problems with components for which no issues had previously been identified).”
Salvador says the answer to this question is a matter of priority—understanding a particular aircraft part's typical behavior, trending, and degradation—something that takes a lot of time. “It is even longer when this health monitoring analysis includes implementing failure prediction algorithms models. The priority varies from airline to airline, but priorities should always be assigned based on operational safety first and operational efficiency second.”
Ravvin stresses that movable and mechanical parts generally require more monitoring. “They are more susceptible to wear and tear and accelerated degradation. Latest trends in analytics have moved to provide a larger view of the aircraft, focusing on mechanical parts, sensors, fuel, flight conditions, engines, and electrical systems.”
Since it plays such a vital role, aircraft engines must be health monitored. Engine health management (EHM) is the term Rolls-Royce uses to describe the transfer of data from an engine on an aircraft to an operational center on the ground, which can be used to record and monitor the performance of an engine. This information, when combined with information from the wider fleet, helps inform what the optimum maintenance regime should be. This in turn helps to ensure engine, and therefore aircraft, availability.
“While EHM has been a feature of Rolls-Royce jet engines for decades, and underpins the TotalCare service support that the majority of our customers select, Rolls-Royce’s latest EHM system is capable of measuring thousands of parameters more than previous versions and it can monitor entirely new parts of the engine,” says Rolls-Royce marketing manager Stephen Lancaster. “Our latest EHM systems can reach parts we haven’t reached before and deliver much greater detail on request. 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.”
After initially being used in military helicopters in the late 1990s and early 2000s, AHM has evolved significantly, with smarter, more precise predictive algorithms, based on history and use cases. Ravvin claims faster and more powerful computing allows for more efficient and accurate data aggregation. “[The] latest advances in Wi-Fi, Cellular, and Satcom have pushed HUMS to grow in the same direction. Overall, the products are smarter, faster, more precise and now provide the ability to interface with cockpit and flight management systems for complete aircraft performance overview.”
AHM used to be based mostly on data collected from ACARS reports, which are mostly produced by the (Aircraft Condition Monitoring System) ACMS. However, Salvador says ACARS reports contain data that is collected with a limited frequency and only represents what happened in one or, at the most, a few seconds during a flight when a particular condition has been detected. “While this type of data still has a lot of value, it is not enough anymore. AHM analysis has evolved to make use of more data sources, such as the QAR/DAR data, that allows operators to have a holistic view of what happened during the whole flight, before and after a specific flight condition took place. QAR/DAR data also allows operators to perform retrospective analysis and use this data to monitor, in the future, different components that they are not monitoring now.”
A breakthrough technology that Anderson says everyone is talking about is the application of ML and AI to data. “Applied to the data gathered from OT systems on the aircraft, AI/ML can help operators identify and address issues sooner, which can help them run maintenance operations more efficiently, reduce costs, and ultimately provide a better and more reliable traveling experience for their customers.”
At Rolls-Royce, engine health monitoring services have evolved via continual improvements in digital technology allowing it to transmit more engine-related data and process that information to help inform service management. “Improvements in digital visual quality and the ability to transmit from a wider range of locations have enhanced remote inspection techniques,” Lancaster says. “This understanding has to be applied by our engineers, and our understanding of our own products has increased over the years as our engine fleet has accrued millions of engine flying hours in service.”
It is critical that AHM information be interpreted by a combination of data analysts and domain experts in the component segment that is being monitored. Salvador cautions that a data analyst cannot distinguish if a component is behaving normally or not without the support of a domain expert, and a domain expert cannot draw adequate conclusions from the data until the data analysis presents the data in a clean and helpful format.
Ravvin cites the following types of AHM data that can be collected:
Usage monitoring: Collection of events and times spent operating aircraft and subcomponents
Exceedance monitoring: Detection of out-of-limits operational characteristics or parameters
Data and event recording: The storage of raw and processed data, events, and activities
Balancing (rotor track and balance, shaft balance): Smoothing and optimizing of vibrations
Mechanical diagnostics (airframe, gearbox, shaft, and bearings): Analysis of rotating parts
Data integration: Consolidation of all available aircraft sensor data
There are multiple processes for analyzing this data correctly. Hall says two of the more popular ones are range checks and consistency checks. “Range checks involve ensuring that the values that should be appearing within specified ranges are, in fact, present. For example, if data pertaining to cruising altitude matches the OEM-specified range, it will pass. Consistency checks involve cross-checking reasonableness of measurements with other measured parameters. For example, if pressure readings should be a certain range within a certain altitude, but they are not matching, it can allude to a potential data validation issue. These checks allow us to see how well analytical predictions from AHM programs tie in with maintenance and overhaul experiences of operational aircraft.”
