A magneto is the one component on your piston engine that will stop the aircraft cold if it fails — and unlike most accessories, it is on a fixed maintenance clock. This guide explains how aircraft magneto overhaul actually works, when your unit is due, what separates an overhaul from a repair, and how to read the paperwork that comes back.
What a magneto does, and why it wears out
A magneto is a self-contained ignition generator. It produces the high-voltage spark your engine needs without drawing on the aircraft's electrical system — which is exactly why certified piston aircraft carry two of them. That independence is a safety feature, but it also means the magneto lives a hard life: it spins continuously whenever the engine runs, its contact points open and close millions of times, and its internal components accumulate wear no visual preflight will reveal.
Left unattended, a worn magneto shows up as a rough mag check, hard starting, or — at worst — an in-flight ignition failure. The whole point of a scheduled aircraft magneto overhaul is to reset that wear before it reaches the runway.
When is your magneto due?
Most manufacturers publish two intervals: a 500-hour inspection and a full overhaul (commonly at engine TBO, or on a calendar limit). The exact numbers depend on your model and the applicable service documentation, but the practical triggers are:
- At the 500-hour mark — a scheduled inspection to the manufacturer's kit, addressing the contact assembly and wear items.
- At engine overhaul — magnetos typically come off and go through overhaul alongside the engine.
- On symptoms — a failed or rough mag check, hard starting, or unexplained roughness.
- On the calendar — some limits are time-based regardless of hours flown, which matters for low-utilization aircraft.
If you are unsure, the fastest way to find out is a bench test — it produces recorded performance data rather than a guess.
Overhaul vs. repair vs. bench test: know what you're buying
These words are not interchangeable, and the difference is money.
| Scope | What it is | Best when |
|---|---|---|
| Bench test | Performance verification, no teardown, ~1 day | You need to know if the unit is serviceable |
| Repair / IRAN | Fix a known discrepancy; inspect and repair as necessary | A specific fault, or “open it and tell me” |
| Overhaul | Full teardown, every life-limited part replaced to kit | Due at interval, or coming off at engine TBO |
An overhaul is a defined scope: the unit comes fully apart, every component is measured against manufacturer limits, and every item the overhaul kit specifies is replaced regardless of how it looks. A repair returns a unit to serviceable condition; an overhaul returns it to a defined baseline.
The models and kits we overhaul
Aircraft Accessories Florida works to current manufacturer technical data on the most common piston magnetos:
- Champion Slick 4371 — overhaul kit MK 401, 500-hour kit MK 431
- Champion Slick 4370 — overhaul kit MK 402, 500-hour kit MK 431
- Continental dual magneto 10-682910-18 — overhaul kit MK 601, 500-hour kit MK 631
- Continental S6LSC-204T (P/N 10-600646-201) — by model
Standard turnaround is three to five business days from an approved quote. See the full model and kit table.
How a proper overhaul is controlled
Any shop can replace parts. What separates a defensible overhaul from a hopeful one is control — and the single most important control is the NDT gate. When a component needs fluorescent penetrant inspection (FPI) to reveal cracks, AAF sends it to an approved outside vendor under the specified ASTM E1417 method. Until that result is received, verified, and accepted, no part proceeds to paint, assembly, or installation. The unit does not leave the hold. That is the rule that keeps a hidden crack from being painted over and shipped.
Every unit also carries one work order number that holds its entire history — every inspection result, every part with its trace, the AD and service bulletin review, and the final release. See the eight-stage process.
What comes back: the FAA Form 8130-3
When the work is done, your magneto returns with an FAA Form 8130-3 airworthiness approval tag. It identifies the unit by part and serial number, states the work performed, cites the technical data revision used, and is signed in Block 14 under the repair station's certificate. That form is what makes the unit legal to install — and it is the first thing an inspector or a buyer will ask to see.
Magneto overhaul questions
How much does an aircraft magneto overhaul cost?
How long does a magneto overhaul take?
Do I need to overhaul both magnetos at once?
What is a 500-hour magneto inspection?
Can you overhaul my magneto if I'm not in Florida?
Ready to get your magneto overhauled?
Send us your model, part number and serial number, and a note on what you're seeing. We'll confirm the unit is within our rating and come back with a scope and a price.