Electrical systems are another area that needs special attention. Over the years electrical instruments, avionics, and components are replaced or added, and associated switches, circuit breakers, and wiring have either been replaced, repaired, spliced, or at times left original and can become a real mess.
Gardner says, “We’ve found flight control cables with a heavy coating of oil or a coating intended to protect cables when often times this only hides cable corrosion.”
Best practices and guidance
When asked what best practices he could offer Gardner shares, “Inspect and document everything. Determine which items are airworthiness and safety of flight items, and which items can be considered nice to fix. Inspect all old repairs, look at their prior approval basis, and ask and answer the simple question, are they good quality approved repairs? If so leave them. And most important review the entire aircraft and your findings with the owner so there are no surprises later.”
Earl Lawrence, manager of the FAA’s Small Airplane Directorate Aircraft Certification, shares some of his views. He says, “New technology has migrated down into the aging systems of many older GA aircraft.” Lawrence describes what he feels are three important items on the subject of maintaining older aircraft. They are: Keeping old systems properly working with reduced knowledge of these older components and systems; interface issues between new components and old systems particularly with electronics and avionics; and training of AMTs on modern technology components, systems, and materials, and how new technologies filter down into existing systems and aging aircraft.
Lawrence explains how the FAA has looked at numerous Airworthiness Directives as a result of interface related failures. Many, if not most, older GA aircraft have seen equipment changes, modifications, and significant repairs. Some interface problems can be easily detected such as chafing or rubbing of wire bundles or flight control cables, but interface issues with electrical or mechanical systems are more difficult to detect.
As for routine maintenance Lawrence suggests exercising items you would not consider on a newer aircraft such as circuit breakers to determine if they still function properly. He adds, “What’s wrong with removing, inspecting, and protecting wing attach bolts every 20 years.” He also stresses the importance of data and encourages AMTs to report all examples of fatigue cracking, corrosion areas, as well as manufacturer’s quality escapes.
Information is available
The FAA as well as aircraft type clubs are great resources for information into inspecting and maintaining aging GA aircraft. Here are just a few applicable documents I found on the FAA web site:
Advisory Circular (AC) 23-27 titled “Parts and Material Substitution for Vintage Aircraft” is intended to make suitable replacement parts selection easer and expedite the approval process.
Best Practices for Maintaining Aging General Aviation Airplanes released in September of 2003 was the result of an effort between the FAA and several GA groups, and provides guidance about maintaining the airworthiness of aging single-engine GA airplanes. Among other points this guidance makes, one of the best practices I found applicable is called the Special Attention Inspection. According to this document, as an airplane ages the normal annual inspection minimum requirements specified in 14CFR 43.15 Appendix D or even by the manufacturer may not be enough, and inspection methods and techniques may change from what was originally required. Special inspections may be needed because of airplane history and use, inactivity, storage conditions, previous modifications, or poor maintenance over the decades. This document includes an Aging Airplane Inspection & Maintenance Baseline Checklist and states special criteria pertaining to a specific airplane or type can and should be included.
Roadmap for General Aviation Aging Airplane Programs released by the FAA in September 2006 is intended to be a guide for the FAA’s future efforts to proactively manage the overall airworthiness of aging GA airplanes.
Even though many older GA aircraft have undergone upgrades and extensive repairs, they can be challenging to maintain and require a keen inspection eye, information, parts and material substitution, patience, and at times creativity.
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