A serious issue of safety is involved in the controversy of fiberscopes vs. videoscopes.
Granted, videoscopes with their higher resolution values are superior imaging products. However, that does not necessarily mean that fiberscopes are still not capable of providing serviceable imaging qualities.
The issue, however, seems to be at what level of sustained fiberbundle damage is a fiberscope no longer a reliable tool to be a dependable imaging tool in order to certify an engine inspection as acceptable.
At the Mid South Aviation show recently held in Nashville, TN, sponsored by Middle Tennessee State University (MTSU) and the Nashville FAA office, I was invited to present a 45 minute session discussing fiberscopes and their characteristics. This was a workshop discussion of fiberscopes in use in different conditions of damage and disrepair. Four different models of diverse brands were passed out to work groups and they were tasked to identify the damage to the unit and possible causes.
Of the many points of interest expressed by the attendees was the lack of information offered by the manufacturers beyond operating and maintenance instructions as to when a fiberscope was no longer serviceable for certification of inspections. Also missing was an understanding of the possible correlation between eye, brain and prior knowledge of the object to be viewed. Particularly the issue of broken fibers or “black dots” and “half-tones.”
Optical fiber bundle manufacturers declare two broken fibers and three half tones are acceptable for new scopes. With time these broken fibers not conducting light, (black dots and half tones, broken but not totally separated fibers) may deteriorate to more black dots and incomplete imaging in faded or gray tone areas within 90% of the viewing area. A matter of perception now comes to play in the inspection process.
Is the image viewed the true image or is the eye and prior knowledge of the required inspection filling in for the incomplete or damaged fiberbundle?
Are three or more scattered black dots and an undetermined number of grey half tones cause to not certify an inspection? How about four or five? What is x number too many and when does cost of repair or replacement become the deciding factor?
Is the economic factor more decisive than the safety factor of an uncertain inspection ?
Obviously safety should be the criteria that the FAA expects as a deciding factor but there is no guidance available from manufacturers besides the obvious, anything in excess of the new scope specifications is not acceptable nor will they commit to a number beyond what engine OEMs may consider acceptable.
So the discussion continues and the responsibility falls on the chief inspectors or borescope user to decide the critical question: “Would you certify and fly an engine like that?” and the general response from attendees was a very wise decision: "Be careful what you sign.”
Then the discussion reverted to the choices available besides fiberscopes.
Obviously as a videoscope manufacturer and reseller we distribute both videoscopes and fiberscopes. We recommend economical videoscopes of good quality that will provide a high resolution image in excess of 400+X 600+ pixels.
Engine manufacturers (OEMs) will always call out the required inspections in their manuals and fabricators will continue to respond to their requirements.
The question was asked, "Will we sell you a fiberscope?" Yes, but a videoscope that will outlast a fiberscope 3 to 1 in longevity, give you a higher quality image, add a built-in capability to record the inspection at one third or slightly more the cost of a fiberscope is definitely the better option.
The presentation concluded with a new appreciation of the risks and advantages of upgrading existing equipment to the best available visual inspection equipment. The lack of exposure to videoscopes in different applications was clearly a point of interest and as always the financial considerations will be a factor. However all agreed that the best equipment for safety and security in the aviation industry should be the primary factor in the decision making process.