Borescopes, an Inside View

Sept. 5, 2023
Borescopes provide an inside look at areas of an aircraft too small to otherwise see. But knowing what kind of borescope and what features it needs to get the job done can take a few glances.

In lieu of X-ray vision, the borescope is the tool technicians need to get a look at the inside workings of the cramped and small spaces of aircraft. And while it’s essential equipment, that doesn’t mean there aren’t essential questions to ask when it comes to borescopes and their use. For example, how does a person know what kind of borescope is right for the job?

Bill French, sales representative, USA Borescopes, said the answer can be pretty simple on the surface when it comes to knowing what kind of scope to use.

“The best borescope is the one that does everything you need and fits in your budget. The range of borescopes in features and functions is pretty wide, and it really depends on what advanced features you’re looking for and as well as your budget,” said French.

With that in mind, a technician is going to need to know the ins and outs of the different borescope options out there to determine which is the right one for them.

The Right Scope for the Right Job

Broadly, borescopes fall into three primary categories: rigid, flexible and fiberscope. Each borescope has a role to play in a given industry, explained Masateru Ito, marketing specialist for remote visual inspection, Evident.

“There are a wide variety of borescope types due to the different scope diameters, insertion lengths, measurement capabilities and accessories, such as retrieval tools. Borescope specifications differ according to various industry standards and applications. The borescopes must meet the performance requirements for inspections as stated in the manuals issued by aircraft manufacturers, such as the Aircraft Maintenance Manual (AMM) and the Standard Practices Manual (SPM), as well as engine OEMs,” he said.

Rigid borescopes were some of the first created, and while still in use today, flexible scopes are what most aviation technicians are going to need.

“The main types of flexible borescopes utilize a video chip format with internal feature options of articulation, image and video capture, measurement and angle of view at the end tip options,” explained Jerry Ewert, CEO and President, JME Technologies. “It can be challenging to choose the correct borescope. The application for the borescope use must be determined.”

Knowing what kind of scope to use is just one part of the equation. Deciding what features and functions you need a borescope to perform is equally important as to knowing what options you don’t need. French compares shopping for borescopes to car shopping.

“What I tell folks is we’d all love to be driving around in a brand new, decked out Mercedes S-Class, but unfortunately, we all can’t do that. We recognize that there’s other vehicle options that can meet our requirements and fit in our budget. So heated seats, heated mirrors, other fancy options are nice to have, but do you really need that to get from Point A to Point B? And the same is true of borescopes,” French said.

In aviation, having an articulating borescope, one where a technician is able to maneuver or steer the tip of the probe in different directions, is often crucial.

“You’re able to maneuver or steer the tip of the probe in different directions. And so, some do that in two ways. Some do it in four-way. Others do it in a joystick, 360 degrees,” said French.

Another factor to consider is reachability.

“If it is for aircraft engine inspection and general use, the internal accessibility port, length and the angle view to the blades required for the borescope will dictate the best choice for the borescope. The most common borescope size used is a 3.9-4mm or 6mm diameter with a 1 ½ meters to 3 meters length,” said Ewert.

Ito adds that since various types of engine inspections are required, from small engines in small aircraft, such as helicopters and business jets, to large engines in large passenger aircraft, scope choice will change depending on the job.

“Borescopes with different scope diameters and insertion lengths are required for each type of engine inspection. For this reason, a borescope with interchangeable scopes is efficient in terms of saving costs and managing inspection equipment when various types of engine inspections are required,” he continued.

Then comes observational performance. French says image quality can be a big difference maker when deciding on a borescope.

“Are you okay with VHS quality, or do you want DVD, or do you want Blu-ray? The image quality is a big difference,” he said.

With image quality also comes image capture, with some probes able to capture multiple angles and switch between different points of view with just the press of a button.

“Some of the newer systems that we offer have a dual-camera probe,” French said. “So the probe has a front-facing camera and a side-facing camera on one probe. And that makes it nice for guys in that they don’t have to worry about losing a tip, cross-threading a tip, pulling the probe out to have to put a tip back in, then try to get back in the same spot. You just push a button, and you can toggle between those two views.”

Finally, Ito explains that diagnostic performance should always be considered for borescope needs.

“It is important to select a borescope with the excellent resolving power and a wide measuring range that can measure defects such as cracks, corrosion, curls and dents from a greater distance. This can be done using a measuring optical adapter with a deeper depth of view (DOF) and a wider field of view (FOV).

“While the wide measuring range is useful for measuring large defects, the ability to measure from a greater distance provides another important advantage — inspection speed,” Ito said.

Putting It to Use

Once the right borescope for a technician’s needs is in hand, the next step is knowing how to use it. Each borescope will have a learning curve to it which can vary depending on its features, said Ewert.

“There is a learning curve on first use of a borescope. Utilizing the borescope features will take some time hopefully supported by clear manual instructions,” he said.

Ewert said some general rules of thumb include first reading the manual and verifying the internal features and limitations of the borescope.

“Test and understand the articulation, lighting control, image capture, image storage. Determine how you will set up your physical body and scope position to maximize the ease of inspection,” he continued.

For those looking to become certified and all-around masters of borescope-based maintenance, there is advance training that can be undertaken. Using airlines as an example, Ito said post-employment certification consists of three main levels of training:

  1. Post-employment training to obtain aviation-related national certifications. Examples include national certifications for mechanics from the Federal Aviation Administration (FAA), European Union Aviation Safety Agency (EASA), and Civil Aviation Administration of China (CAAC). This training takes approximately five years to complete.
  2. Training to obtain in-house certifications for each aircraft model and engine model takes about six months to one year to complete.
  3. Continuous training is required to obtain new internal certifications, renew certifications and maintain certifications.

For those who merely need to use a borescope routinely or less, French said there a number of factors to keep in mind to ensure the equipment is protected and used properly. First is heat.

“Some of the borescopes out there will have a temperature sensor at the tip. So if the mechanic puts it into the engine, the engine’s too hot, it’ll give a warning on the screen to remove the borescope and, ‘It’s too hot. Cool it down.’ Others don’t do that, so the mechanic needs to have the whereabouts to know, ‘Hey, this engine needs to be at ambient room temperature before I stick this thing in here,’” French explained.

Heat can have such an impact as a borescope is a delicate piece of equipment. French said he stresses this point often.

“The biggest thing, for us, that we try to tell folks is that the borescope is a delicate instrument. The probe is flexible. There’s a lot going on in that little probe. There’s the communication ribbon to the camera chip at the tip of the probe. There’s LED lighting. There’s cables that guide the articulation. There’s a little umbilical cord. It’s kind of like the rib cage of the borescope itself. So the number one thing is it is a relatively delicate tool. It is not a deburr tool. So you see something that’s in your sight of view, and we don’t use that borescope to plunge it out,” French continued.

Another rule of thumb is to treat it like your thumb.

“If you’re okay sticking your thumb in it, we’re okay putting a probe in it. So, ‘You wouldn’t expose your hand to hydrochloride acids, so don’t put the probe tip in it. Would you be opposed to putting some oil on your hands? No, that’s okay. Well, same with the probe.’ So we treat it as the extension of the operator itself,” he said.

A common mistake made is overestimating the durability.

“In appearance the borescope looks like a strong metallic cable connected to a monitor but internally it is a complicated instrument. It is utilizing a monitor processor computer with software connected to a cable that internally has ultra-thin wire connections to the chip, to the lighting, for the articulation, all connected and working in sync together,” Ewert said.

Case installation and removal can also be an issue. Ewert said to make sure to install the scope properly, so it is not partially outside of the case when the case is closed. And an easy way to keep a borescope safe is by minimizing who uses the scope so that only those properly trained on it use it.

But if a unit is damaged, borescopes can be repaired at a cost.

“The borescope is a complicated instrument. It can require significant parts and labor in cost to repair. What appears to be minor damage may require almost a complete rebuild of the instrument. Often multiple repair costs will exceed purchase cost for the customer,” Ewert said.

French said the most common issue they see with borescopes in need of repair is with articulation.

“The cables that actually perform the maneuvering or steering at the tip of the probe, those cables run through the tip all the way up into the body of the handle. So in most cases, unless it’s just a simple solder weld, when those cables are replaced, the articulation cables, a light-guide cable, a communication ribbon to the tip of the probe, it requires an entire breakdown of the system,” French said.

And depending on what model you have and how long the probe is, the price in the labor and time it takes to repair, varies.

“Of course, in some of the more advanced systems that have electronically assisted articulation, the articulation may be with the cable. It may be with some of the electrical components or diodes or contacts with the actual electrical part of the articulation. So it really varies as far as cost, time, and labor,” French continued.

To avoid repairs, French said the number one best practice to follow is to go slow with the borescope.

“It is an intricate piece of equipment that’s performing a high-level inspection. We’re not rushing it. We don’t treat it like something that is disposable. So move slow with it. We want slow movements, nothing jerky. When we remove the borescope probe, we don’t pull it out like we’re trying to start a lawn mower. We don’t want to whip it out, and we don’t want to force it into channels that, when you feel there’s restrictions, we don’t want to try to force it around. We want to try to understand what’s restricting it, adjust or remove the restriction, then move forward,” he said.