Borescope inspections are a routine but vital part of engine maintenance but combining with new technologies is opening up new opportunities. Ian Harbison reports.
Borescope inspections (BSI) are an essential but intrusive technique to establish the internal state of an engine. Given that they have to penetrate the outer case of the engine, Adam Mallion, senior business and project manager at OC Robotics, says borescope access points might be essential but they are complex and costly to engineer. While some engines have more than others, he expects future engines will have fewer, with the design emphasis being on finding the best location for the greatest access to the engine’s inner workings. These will not only be designed for BSI but will be to handle other tools for a variety of purposes.
OC Robotics
UK-based OC Robotics, which specializes in snake-arm robots, was acquired by GE Aerospace in 2017 after it became involved in the development of the HPT Blade Inspection Tool (BIT) for GEnx-1B engines on the Boeing 787 and GEnx-2B engines on the 747-8.
BIT is used for HPT Stage 1 and Stage 2 blade inspections. Unlike traditional borescopes, which use stereoscopic tips to generate a 3D map of the environment and require regular calibration, BIT uses a simple one-hand installation process, with fixed position cameras, to provide consistent, high-quality images of the blade and knowledge of the blade geometry to provide a simple measurement process. The images are processed using AI technology, which can be used to measure both lines and areas on blade surfaces, to make an accurate assessment of the condition of hardware.
A standard inspection can be carried out by one person (two for a standard BSI) in 45 minutes (up to 15 minutes more for BSI). A more detailed Significant Measurement Required can take up to 90 minutes (four hours for BSI).
The information can be exported to a USB or PC and is automatically uploaded to the GE cloud, creating a safe and secure backup of inspection data. The User Interface (UI), developed with airline inspector feedback, groups images together to reduce operator burden. Operators can flag blades of interest and add notes, which will appear in an automatically generated inspection report at the end of the inspection.
Ease of use is important for operators in harsh conditions, such as Africa, China and the Middle East, where high temperatures, dust and sand can adversely affect engines and so inspections tend to be more frequent. Mallion says the huge amounts of data generated by BIT inspections means that predictive maintenance techniques can now be utilized to refine the inspection intervals, and over time, the maintenance intervals, optimizing shop visits.
However, the company’s MiniX snake-arm robots are being developed to use the BSI access point for other purposes. These are self-supporting and can be precisely controlled to obtain access to other areas of the engine. Applications include cleaning, boroblending (minor repairs in situ) and reapplication of thermal coatings.
Dr. Jan Oke Peters, engineer technology development, explains, “I think it is safe to say that the engine OEMs learnt a lot from MRO experience gained over the decades with the predecessor ‘bread and butter’ models such as CFM56 and V2500. The latter model’s high-pressure compressor (HPC) proved especially tricky for borescope inspections as it only offers seven borescope inspection locations for ten stages, and only one borescope access point for the complete LPT (low-pressure turbine) module.”
or in specialized repair shops.
Lufthansa Technik image.
He says that, in contrast, new generation engines such as the PW1000G and LEAP families have one borescope port for each HPC and LPT stage. This significantly improves accessibility for MROs, and moreover opens up the possibility to inspect both the leading and trailing edges of two successively positioned stages through a single port. In addition, the newer engine types feature an additional borescope port in the first stage of the high-pressure turbine (HPT) nozzle. This extra port greatly eases the inspection of the trailing edge of the Stage 1 HPT nozzle and the leading edge of the Stage 1 HPT blades. On older engine types, access to this complex location always required the use of a flexible borescope, which, in a complicated move, had to be inserted in the combustion chamber and between the airfoils of the HPT nozzle.
Lufthansa Technik
For Lufthansa Technik, the add-on technology was a 5G campus network in Hamburg, which started operations in 2020 in an engine workshop dedicated to CFM56 and V2500 overhauls.
Before that, borescope inspection (BSI) activities regularly comprised both routine/scheduled as well as unscheduled/on-condition inspections. The former category, for example, included all inspections mandated in an engine manufacturer’s maintenance schedule or Maintenance Planning Documents, as well as OEM Service Bulletins. The latter category for example includes post-bird-strike inspections or cases in which an engine experienced abnormal vibrations or a sudden drop in the exhaust gas temperature (EGT) margin.
In addition to that, the company performed inspections during every overhaul shop visit, both on incoming engines as well as on outgoing engines. Other noteworthy fields of activity comprised both off-wing and on-wing borescope inspections on leased engines, for example, during a transfer of ownership or from returns from lessee to lessor.
Of course, initial operations of the network coincided with the COVID-19 pandemic. “Now aviation has left the ‘crisis mode’, current BSI activities are not that much different than before pandemic situation,” Peters says. “Except maybe in the aspect that, during the crisis, we significantly expanded our product offerings in the direction of Mobile Engine Services (MES), our term for smarter repair and lifespan-extending solutions. These can avoid or postpone major overhauls and can be carried out on-wing, on-site or in specialized repair shops. This segment still enjoys significant popularity and it is another interesting field in which we can put our comprehensive borescope expertise to good use.”
Michael Kirstein, vice president operations engine services at Lufthansa Technik, says: “Since the pandemic situation, virtual parts inspections and digital borescope inspections have clearly gained acceptance in our company. In fact, the Virtual Table Inspection (VTI) quickly advanced from a test project to a business-critical infrastructure, as travel restrictions prevented customers from travelling to inspect their engine parts. The 5G-based video streams have helped us enormously. In the past, such inspections often had to be planned several weeks in advance. Now we can schedule inspections at very short notice, which our customers really appreciate.”
In 2021, the 5G-powered VTI was fully integrated into the company’s AVIATAR Digital Operations Suite. Peters comments that this connectivity to digital technical operations and fleet management platforms is an important focus area in the further development of borescope equipment. A seamless connection to offerings such as AVIATAR can greatly improve the cooperation and interaction between the borescope inspector at one end, the engineering team in the middle, and the customer at the other end.
In his view, the quality and resolution of borescope imagery has constantly increased, and today’s state-of-the-art equipment already delivers a video quality that fulfills the requirements of many smart software tools and solutions utilizing technologies such as artificial intelligence or machine learning. The company is currently preparing the first such technique for entry-into-service in the coming months in line with tailored repairs within the MES portfolio.
From a pure application point of view, Peters can see a few development steps delivering further improvements to the entire borescope process. One very important driver emphasized by Peters is standardization. A consistent positioning of the sensor and camera, for example, could help to create more reproducible views that would significantly improve the reliability of the inspection results, even when performed at very different repair stations or locations. More standardized procedures could also help in the measurement of defects, providing more consistency, more accuracy and higher speed (shorter turnaround times), he believes.
Another trend he sees is the growing use of hardware and software to provide smart assistance for borescope inspectors. Here, for example, AI will definitely play an important role. Concerning flexible borescopes, upcoming development steps will presumably focus on aspects such as improved durability of the bending sections or improved articulation.
Finally, he says an additional focus area on the Lufthansa Technik development roadmap for borescope technology is the corresponding tool landscape. The aforementioned software tools supporting borescope inspections by utilizing AI for various (often niche) applications are only one example in this regard. Another good example is the development of special guidance or navigation tools (usually hardware but also software) that help improve the accuracy of the positioning of the sensor head in order to optimize the borescope’s view. Another tool which is under development aims at automatically turning the N1 spool during the inspection. This purposeful and target-oriented future development of the company’s borescope equipment and techniques, could probably even lead to the development of entirely new on-wing repair solutions for the MES portfolio.
Recently, the network was extended to a second workshop handling LEAP and CF6-80 engines. The company emphasises that customer decisions often involve six-digit cost figures, so the high resolution video and the stable, reliable and confidential 5G connection to the customer are essential. In fact, in one case, it demonstrated that scratch marks of just 0.3mm in length could be reliably identified.
One unusual aspect of the operation was the engine facility’s location on the edge of Hamburg Airport, so there were concerns about possible interference from the 5G network with aeronautical services, as has happened in the U. S. As it happens, the frequency band used by Lufthansa Technik is between 3.7 and 3.8 GHz. Compared with the public 5G band in the United States (3.7 to 3.98 GHz), the safety margin to the frequency band used by radar altimeters on commercial aircraft (4.2 to 4.4 GHz) is twice as large. In addition, Lufthansa Technik has so far employed 5G technology exclusively inside industrial buildings, which, with their high steel and concrete content, massively shield all wireless networks from the outside world.
MTU Maintenance
Within MTU Maintenance, borescope inspections, boroblend repairs as well as other on-wing or near-wing repair workscopes are performed by its ON-SITEPlus service teams, who can rapidly deploy to where they are needed from regional service centers in the USA, Germany, Canada, Brazil, Australia and China. If blade damage is detected and repairable, MTU can perform boroblending on CF34, CF6-80, CFM56, GE90, LEAP PW1100, PW2000, and V2500 engines.
MTU’s head of on-site services, Arne Straatmann, says, “Although MTU uses state of the art equipment and technology, the key element remains the skill and expertise of our inspector combined with the knowledge of our extensive network. In addition, it sometimes pays off when we perform BSI inspections that we have much more knowledge to judge any damage because we design, manufacture and repair airfoils, so we know the product in depth.”
Straatmann adds, “The ON-SITEPlus service team always try to keep an engine on wing if possible. We are always monitoring the latest digital technologies and indeed we are sure that AI-based applications will play a significant role going forward. This new technology actually enables us to reduce effort and time while at the same time even further increase quality. It is this consistent quality that enables MTU to be the only provider in Europe of OEM approved HPC boroblend repairs for the V2500 family.”
Aiir
Another company using AI is Amsterdam-based Aiir Innovations, which was formed in 2016 after the AFI KLM E&M engine shop in Amsterdam invited an assistant professor in Computer Vision and five graduates in Artificial Intelligence to see if they could develop a system to automatically analyze borescope video streams to identify faults such as cracks, scratches and dents. Bart Vredebregt, CEO and co‑founder of Aiir (and one of the students) says that initial results were promising but it took a few years to return to AFI KLM E&M with a viable product.
The Aiir software, which includes automated blade-counting, uses image analysis to very quickly generate a report — damage is flagged before the camera probe has even left the engine, while historical footage can be reviewed online. Video and other files are loaded on the company’s cloud-based platform and reviewed by the AI software. A detailed report then highlights any defects or damage detected. If further analysis is needed, comments can be left next to the relevant image. Other team members can see these immediately via the platform and offer their own evaluation. By generating a secure link, third parties can also access images and footage, eliminating the need to email large attachments or screenshots.
As well as AFI KLM E&M, users include Regional Jet Center in Amsterdam, which specializes in maintenance of Embraer E170, E190 and Lineage aircraft. The system was also trialled by easyJet in 2021.
It has also been incorporation into the Everest Mentor Visual iQ (MViQ) VideoProbe from Waygate Technologies, where it runs offline, while a further variant is Aiir Lite.
This is a standalone still image version of the analytic used by the Aiir Inspection software. The analytic was trained using more than a thousand hours of borescope footage from a wide variety of clean and dirty turbine engines including CF34, CF6, CFM56 5A/B/C, CFM56 7B, GE90, GEnx, LEAP, PW 1100, PW 2000, Trent 700, Trent 1000 and V2500. To enhance analytic robustness, images were captured from a multitude of incident angles and stand-off distances from the target component during historical borescope inspections.
It is available in two versions — Aiir Lite – Combustor and Aiir Lite – Rotate. The first covers the combustor, and sections of the high pressure turbine with Thermal Barrier Coatings, the second covers the high, intermediate, and low pressure compressor, intermediate, and low pressure turbine.
In a separate development, Aiir Innovations has been selected as one of eleven new startups to join the fourth cohort of Aerospace Xelerated. The program, led by industry partner Boeing in partnership with Tawazun Council, the defence and security acquisitions authority of the United Arab Emirates (UAE), is supported by the Defence and Security Accelerator (DASA), GKN Aerospace and Etihad Airways.
The 11 startups, chosen from a pool of over 150 applications from around the world, will cover the program’s key focuses: Flight & Passenger Journey Optimization; Supply Chain Intelligence; Next Generation Workforce; and Operational Efficiency. They will benefit from a £100,000 investment from Boeing, with potential for additional funding from partners. Through Aerospace Xelerated, startups will be introduced to a network of angel investors, venture capitalists and key stakeholders amongst the aerospace industry, throughout the 12-week program. Successful companies will also get more than £100,000 in program benefits from partners including startup providers Oracle, Amazon, HubSpot, Digital Ocean and many more.
Eyes on the Inside
While there is optimism around technologies like AI, there also has to be some caution. One of the problems with AI is that many projects fail because they are ‘innovation for innovation’s sake’ and that they fail to take enough account of human involvement, especially when there is no associated legislation in place. As a result, while prototypes may be easy to create, they are difficult to get accepted by workshop personnel, who can see it as a threat to their jobs, being replaced by a machine.
In addition, in a safety critical environment like commercial aviation, it is important that there is complete confidence in the results. Numerous research projects have fooled AI visual recognition systems into misidentifying or, more importantly, missing vital details.
It is interesting to note that Waygate Technologies publishes an important caveat: “Analytic applications are intended to assist the user whilst performing in-situ visual inspections. Results will vary depending on your application. State-of-the-art analytic applications are generally not 100% accurate and this analytic is no different. Do not rely on this analytic to detect all indications.”
BSI is here to stay but its evolution will see connectivity, AI and colocation with other tools as the way forward.