Boroscope inspections involve looking at components within an engine using an optical probe. The probes are inserted in to the engine through ports in the engine casings, and can be rigid or flexible, the choice being dependant on the difficulty at obtaining a satisfactory view of the required features. Some of these inspection ports are the attachment points of other functional devices that intrude into the engine (e.g. ignitor plugs or temperature probes) but on more modern engines there are usually several purpose made ports for boroscope inspections.
In general the boroscope inspection technique saves many hours of work and can reduce the down time of the aircraft in many cases, disassembly and reassemble of the engine not being required. The boroscope is essentially an eyepiece connected to a rigid or flexible tube. The tube contains fibre optic cables that carry light and therefore visual images, even when the tube is made to bend through considerable angles. A second fibre optic cable within the tube carries light from a bright light source to illuminate the target. At the end of the tube there will be a viewing lens, with a light source lens nearby. Most flexible probes have a steerable tip which allows the operator to steer toward the target, and the lens is mounted in the tip to view straight ahead. Rigid probes may have prisms behind the lens to allow the probe to view at right angles or 45° to the probe.
The operator inserts the probe into the appropriate port to view the internal components. Some techniques require the use of guide tubes to ensure that a steerable probe is going in the right direction. Ports are usually designed into the compressor, turbine and combustion sections of the engine. On the viewing end of the boroscope there will be the controls for the steerable tip (flexible probe) and to allow the operator to focus the probe. It is more usual these days to find a video camera attached to the eyepiece so that a recording of the inspection can be made. The video is presented on a television screen that allows a much bigger picture and also more than one person to view the screen. The recording is useful as sometimes it is very difficult to find or reproduce a view that may fleetingly pass and which gives you concern, also should a problem be observed it can be dispatched to the manufacturer for analysis by their experts. When turning the engine careful counting of the blades or number of turns of the hand turning point is required to ensure that all of the blades have been viewed.