Aircraft maintenance: When to overhaul an alternator

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On one hand, we operate in a strict regulatory environment governed by the federal aviation regulations (FARs). On the other hand, our job as aircraft mechanics (A&Ps) and inspectors (IAs) is to utilize our experience and cumulative knowledge to keep our ever-aging fleet of general aviation aircraft flying safely and reliably. The FARs are the starting point, but mechanics make recommendations on many additional items based on a maintenance philosophy developed from years of experience. A good mechanic “practices the art of aircraft maintenance” just as a doctor practices medicine.

I tend to subscribe to the philosophy of “First, do no harm.” Every time a system is disassembled for maintenance, the opportunity exists to induce failures. Therefore, I am deliberately conservative about the components on an aircraft that I will proactively disassemble, inspect, overhaul, or replace without performance-based cause. For aircraft operating under Part 91, this gives us a fair amount of leeway. Manufacturer-recommended time between overhauls based on hours or calendar time, and even service bulletins, is voluntary for Part 91 operators. Research and experience guide the recommendations we make to owners regarding compliance with non-mandatory maintenance. My personal checklist for these items looks something like this: Does a failure of the affected component affect safety of flight? Does the affected component typically fail gradually, or catastrophically? Does the component have a predictable wear trend? Can the health (or wear) of the component be monitored?

Careful consideration of these questions results in my personal philosophy regarding “monitoring” versus “proactive intervention.” When it comes to engine accessories, my “proactive intervention” list is short, with magnetos and alternators topping the list. And that brings me to my most recent replacement (and upgrade): the alternator.

For anyone who flies IFR, the loss of an alternator immediately puts you on borrowed time to get on the ground before you lose critical instruments (for glass panels), communication, and navigation. Therefore, the health of the alternator is critically important. That means more than just checking and replacing worn brushes. It means ensuring that the bearings are in good shape, that the diodes are working, and that the unit as a whole is putting out its designed power capacity, something that can degrade over time.

On aircraft with gear-driven alternators (Bonanza, Baron, Cirrus, etc.), there is an additional risk in that the alternator is directly connected to the engine through a ring gear on the crank

This post was originally published by AOPA on . Please visit the original post to read the complete article.

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