Borescopes: An Inside View


Those of us who work in helicopter maintenance are familiar with borescopes. Our non-aviation friends and associates of the “baby boomer” generation sort of know what borescopes are as well. The last time they went for a colonoscopy, they got intimate with an endoscope — a medical type of borescope in a loose way of speaking. I asked the HeliMxAdvisory Board to come up with a list of questions on borescopes to cover in this article. As with any topic, the more people you ask for information, the more information you get. In some instances there will be at least two answers for the question asked. The intent is to provide you with a good first step in thinking about and using a borescope.

A borescope is an instrument that works like a medical endoscope. In aviation, it allows mechanics to explore areas of the aircraft and/or engine that are too small, too remote or out of reach through other means. It has an eyepiece at the top attached to an insertion tube that can either be rigid or flexible, and two lenses on the opposite end from the eyepiece. When the bore-scope’s insertion tube is directed through an opening, it allows the lenses to view what needs to be checked. We frequently use borescopes to look inside engines or places inside an aircraft that are not other-wise visible without taking them apart. Since disassem-bling a piece of an aircraft can create more problems and is time consuming, borescope usage cuts out this step and diagnoses problems or determines the sound-ness of a particular part in a way that promotes less work and less time.


There are several different types of borescopes. There are bore-scopes with a rigid insertion tube and those with a flexible insertion tube. These include the various endoscopes used for medical and veterinary procedures. To name a few, there are angioscopes for hearts, bronchoscopes for lungs, colonscopes for colons, otoscopes for ears and gastro-scopes for stomachs. When a borescope has a rigid insertion tube, it is likely to be made from a stainless-steel rod.


British physicist Harold Horace Hopkins invented the rod lens endoscope and the zoom lens. His work made it possible for surgeons to do less invasive procedures using “key hole” surgery. Because the borescope makes it possible to see the in-ternal organs, bones and muscles, a large

incision can be avoided, making it easier and quicker for the patient to recover. The following questions and answers are provided to help you better under-stand what might be considered if you are in the market to obtain a borescope for your maintenance tasks.

Question– When purchasing a borescope, how should you determine which probes and types of lighting used around the camera lens is right for your needs? What type of lighting control is best to have?

Answer 1– A general rule in pur-chasing a borescope and determining the length and diameter is this: never shorter, never fatter. The diameter of the probe is limited by the points of access you have available. The length will be determined by the area you want to access. Lighting options can be dependent on the area that is to be inspected. Larger areas may require more light in order to get a clear view, as opposed to a smaller area where a lower intensity light source can be used. There are many borescope models that have different lighting options. LED, halogen, metal halide and xenon are available, to name a few. Depending on the application, it may be necessary to have an adjustable intensity in order to not wash out the image.

Answer 2 – The diameter and length of the scope (probe) is entirely determined by the engine being inspected. Some engines require 4mm diameter or less, while others can be 6mm or even as much as 8mm. Regarding the length of the scope, smaller turbines generally require 1.3m to 1.5m length scopes, while some of the larger engines require 3m length scopes. The borescope should have controls that are easy to use and intuitive. The image capture and control buttons should be ergonomically placed near the articulation levers. The video monitor menu should be simple and intuitive. Regarding lighting, there are borescopes that have an attached light source. These are typically LEDs; however, most systems give the flexibility of using a variety of light sources, both por-table handheld lights and extremely bright bench top units.

Question– How important is the digital quality of the camera attached to in the borescope?

Answer 1– It depends on the application and what needs to be viewed. For the application of finding debris or block-age, a low-resolution digital camera may be used. If you’re looking for scratches or pitting, erosion, discoloration or sand-sized particles, a higher-resolution digital camera would be required.

Answer 2– The quality of the digital camera is very important, but don’t get too caught up in the resolution. There are many things that make up good image quality such as good contrast, color rendition, dynamic range, signal-to-noise ratio, etc. These things result in good, sharp, clear images. You can have a high-resolution camera with very poor quality images. The best way to determine the image quality is to look at the image. Most people see things slightly differently, as our eyes are different from person to person.

Question– How important is the light source and control of it?

Answer– The light source is very important, particularly when inspecting large dark areas such as combustion chambers. Often when people say they have a bad image, what they really mean is it’s too dark. They need a brighter light.

Question– What are the pros and cons of using a joystick controller?

Answer – Pros: smooth operation, typically allowing articulation in all directions.

Cons: Difficult to feel resistance, which is not good if you are operating inside a tight area where there isn’t enough room for articulation. To counteract this, most units are built with tension relief but gradually articulation will lose strength and need to be serviced by the borescope manufacturer or a qualified repair facility.

Question– If I buy a base model, are upgrades available?

Can I add a camera and lighting?

Answer – Some borescope models are available with upgradeable parts, but most are built to order. Typically cameras that take still photos and video are an option.

Question – Does the borescope manufacturer provide free product training?

Answer– Some manufacturers will provide free training.

There are many borescope products that are very easy to use and do not require extensive training, and often the material included with the unit is sufficient for smooth operation. It’s like buying a camera — read the manual before using it for the first time.

Question– What is the correct way to use the borescope?

Answer – As with most things in life, there is a right way and a wrong way to use the borescope. However, due to the wide variety of applications a borescope can be used for, it can be a trial-and-error basis for some users. Depending on where and how the borescope is used, it can last for years, or just a matter of months or even weeks. With any optical instrument, extreme care with how it is handled and operated is always prudent. When handling or using a borescope, avoid whiplash, dropping, exposure to chemicals, or exposure to large, heavy and unstable objects which could fall onto and crush the borescope. Last are some examples of how a quality borescope helped to resolve some maintenance issues.

1. Prevent an unscheduled removal of a component.

Use of a low-quality borescope (poor image quality and articulation control) can inhibit the ability to make a decision on whether or not a part needs to be changed prior to its scheduled maintenance date. Whether you’re looking for abnormal erosion, discoloration, actual damage, or even if the part is there at all, image quality can play a key part. Also, with the articulation control giving the ability to scan an entire area or the ability to rotate the probe, this is instrumental in helping the operator to see everything needed.

2. Used to locate and recover FOD. In one case of airframe inspection, a borescope can be used to get in through cramped passages in order to assist in the location of FOD. A compact unit is especially handy in this type of application. Using the older units that you have to roll around to each inspection can take up unnecessary time in set up and takes away from actual time do to the inspection. This scenario can be alleviated by purchasing a portable, battery-powered unit so that the mechanic can easily travel from inspection area to inspection area without the need to haul around extra equipment or be constrained by a power cable.

3. Save time and money

Time is money in our business. An aircraft does not make money while it is on the ground. A borescope allows maintenance technicians to inspect necessary components quickly, eliminating the needless downtime of the technician slowly tearing down the aircraft to visually inspect something. Many maintenance facilities know the value of having a borescope available and if one is not in the facility, it’s a huge rush to find one by either renting one or finding an economical option for purchase.

4. Inform timely decisions

The ability to record video and still images proves to be invaluable when tracking the history of wear and tear on aircraft engines, or on normal maintenance items that require periodic inspection. This not only allows you to keep a history of an item that requires periodic inspection, but it allows you to capture an image of damage or any abnormality. This can be advantageous when an inspector finds some-thing that might require a second opinion. Instead of having to remove the borescope, find the appropriate mechanic, then re-insert the borescope tube and spend time trying to find the item again, you can simply snap a picture or record the area in question and show it to the mechanic.

Borescopes are another important tool in maintaining your aircraft. They save you time, money and labor hours in the process. Thank you to staff from Borescopes R Us ( and Gradient Lens Corporation ( for their help with this article.