AC 43.13-1B update provides valuable tips for maintenance of electronics
By Jim Sparks
Over the years, various methods and techniques have been utilized to successfully maintain the worlds fleet of aircraft. Each manufacturer has the responsibility to evaluate any special requirements of their products and then make those of us involved in the upkeep process aware of unique details. These may include inspections, removals, repairs, and even functional tests. The Air Transport Association (ATA) has developed a method for organizing technical documentation in standardized chapters. As the aviation industry's dependency on electronics has exploded in the past 20 years, today's technician needs to have adequate information available to ensure airworthiness.
ATA Chapter 20 is the designated area for manufacturers to publish information pertinent to Standard Practice. This may include, but is not limited to, aircraft cleaning, torque values, plumbing installation and bonding tests. Some manufacturers even have gone as far as to create dedicated manuals of standardized maintenance practices. It is impractical to believe that each manufacturer can document each and every situation.
The Federal Aviation Administration has solicited the creation of Advisory Circular 43.13-1B. This document was issued in September 1998 and supersedes AC 43.13-1A. Contained within are methods, techniques, and practices considered acceptable to the Administrator for repairs and inspection of non-pressurized civil aircraft where no specific manufacturer instructions will apply. To those active in aircraft maintenance who have not as yet reviewed this Advisory Circular, they will find it contains data for inspecting and maintaining newer technology systems.
Following are some useful pointers for properly maintaining electronics systems in aircraft:
Proper bonding and grounding
One of the important factors in the installation and operation of aircraft electrical systems is proper bonding and grounding. A poor ground can lead to improper system operation as well as cause damage due to Electro Static Discharge (ESD). Low impedance paths to aircraft structure are normally required for electronic equipment to provide radio frequency return circuits and for most equipment to reduce the possibility of Electro Magnetic Induction (EMI).
All external aircraft surfaces that are capable of conducting electricity should be electrically connected to other surfaces through mechanical joints. Exceptions such as some antenna elements require electrical isolation from the rest of the airframe. Coupling the return paths from multiple sources should never occur as electrical noise maybe transmitted from one source to the other and can be a significant problem in digital systems.
Bonding inspections should include checking for the presence of electrical arcing. In all cases, arcing should be suppressed either by enhancing bonding or increasing resistance. Any metal conduit should be bonded to the aircraft structure at each terminating point and break. All connections should be free of corrosion and tightly secured as well as installed in such a way as not to interfere with operation of other movable components. Standard threaded screws are typically used in bonding applications, and for the most part, self-tapping screws should be avoided unless specifically called out by the aircraft manufacturer.
Proper wire termination is an area that requires several considerations. First of all, the tensile strength of the wire to terminal joint should be at least equivalent to the strength of the wire.
Proper selection should be based on current rating, wire size and insulation thickness, conductor material, size of the attaching device (stud size or hardware diameter), compatibility with the insulating material, operating environment, and method of attachment.
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