Preventive Maintenance

For those not well versed in the art of aircraft repair, words of caution: lack of knowledge may end up costing more in the long run.

Transponder and altimeter systems are also off limits to anyone not covered by FAR 43.3 and addressed by either Part 91.411 or 91.413. Some gray areas do exist in who can perform a test of a transponder system after a known disconnect of the digital data link. This is clearly covered in Advisory Circular 43-6b and gives return to service authority to those listed in FAR 43.3.

Updating navigational software data bases is another area where pilots can use their sign off authority. This is provided no disassembly of the unit is required and pertinent instructions and training are provided. This privilege can be based on the type of aircraft operation and the sign off in maintenance logs may be an essential step. Prior to the unit’s intended use, an operational check must also be performed.

Heading off failures

Preventive maintenance is by no means limited to pilots. Much of what goes into support initiatives of aircraft today is with the intent of heading off failures. Oftentimes an enhanced situational awareness utilizing many of the body’s sensory organs can have a significant impact in heading off potential problems. Routinely comparing flight displays for uniform brightness and clarity will often provide subtle clues that an instrument may be approaching failure. Touching a unit (carefully) can also provide evidence specifically regarding temperature and vibration. Even audible ques can provide guidance as to the operating state of various components.

As avionic components do depend on electrical power and a byproduct of operation is heat, one of the most important proactive checks is the assurance of proper airflow surrounding the component. Caution must be used when evaluating the location of a device in close proximity to fuselage skin. This is particularly true in aircraft operating at high altitudes for prolonged periods of time. Some documented cases revealed that the heat sink impact of metal component surfaces joined to un-insulated aircraft structure will cause the temperature of the unit to go below the design threshold.

By analyzing the previous repair history of particular units we can identify the parts most susceptible to failure and make arrangement for replacement to extend the component life and overall performance of your avionics. It has been noted that this type of attention will improve system reliability by as much as 50 percent.

Coaxial cables are an area that have for the most part, been considered “on condition.” After all, what could possibly go wrong with a chunk of wire? Antenna cables are generally tuned for the type of system in which they interact and maybe best considered transmission lines. A coax is made up of at least two conductors separated by an insulating material. Breakdown of a coax will result in initial diminished range and clarity of the transmissions and reception and possibly soon followed by transmitter failure. Breakdown in transmission lines can occur from the results of heat, chemical exposure, or even over tightening of cable clamps.

Of course “preventive maintenance” may not always work for the good. Using certain types of automotive wax on aircraft windows or improper erosion tape on antenna leading edges may reduce the ability of these components to dissipate electrostatic charge.

Many in this business are still firm believers in the old adage ”If it isn’t broke, don’t mess with it.” As an ex-airframe manufacturer’s technical representative, my first question to someone calling with a problem “had you done anything to the system prior to experiencing the malfunction?” Most of the time the answer was slow in coming and followed by “I’ll call you back.”

The good news is my phone doesn’t ring that much anymore and I attribute that to being proactive rather than reactive when it comes to the maintenance of aircraft in my care. 


Jim Sparks has been in aviation for 30 years and is a licensed A&P. He is the manager of aviation maintenance for a private company with a fleet including light single engine aircraft, helicopters, and several types of business jets. He can be reached at

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