For most Part 91 owners, the magneto 500-hour inspection is a manufacturer recommendation rather than a federal requirement — but it is the cheapest hour of maintenance your ignition system will ever see, and skipping it is how a $300 job turns into a $1,400 one. Champion Aerospace recommends 500-hour inspections for non-pressurized Slick magnetos in its current maintenance guidance, while Continental publishes comparable scheduled inspection guidance for its Bendix-design magnetos.
The real question owners are asking is not whether to do the inspection. It is what to do when the mag comes off the engine and the shop calls with options: freshen it up, overhaul it, or throw the old one away and bolt on a new one. This article walks through all three paths — plus the electronic ignition option — with the costs, the downtime and the honest trade-offs.
The Short Answer
If your magnetos are under about 500 hours since new or overhaul and they pass the inspection cleanly, do the 500-hour service and fly. If they are approaching 1,000 hours, showing distributor block cracking, or the engine is heading for overhaul anyway, an overhaul or exchange unit makes more sense than repeated patch-ups. And if you own a Slick — the disposable razor of the magneto world — a brand-new unit often costs so little more than a full overhaul that replacement wins outright. Bendix-style magnetos, which are heavier, more expensive and built to be rebuilt, usually go the other way: overhaul them.
Is the 500-Hour Inspection Actually Required?
Legally, it depends on how you operate. Under 14 CFR 91.409, a Part 91 aircraft needs an annual inspection, and a 100-hour inspection if it is flown for hire. Manufacturer service bulletins are not automatically mandatory in that world. Unless an airworthiness directive makes it so, or the aircraft is on a manufacturer's inspection program or a progressive program under 91.409(f), nobody from the FAA is going to violate you for a magneto at 700 hours since inspection.
Flip to Part 135 or Part 91 subpart K and the picture changes. Those operators follow an approved maintenance program, and the magneto inspection is typically written into it. Charter operators do this work on schedule because their program says so.
There is a second layer worth understanding. Your mechanic signs off work under 14 CFR 43.13, which requires using the methods and techniques in the manufacturer's maintenance manual. Champion's Slick Master Service Manual L-1363 and Continental's ignition manuals both describe the 500-hour inspection in detail. Plenty of IAs take the reasonable position that an engine with 900 hours on unopened magnetos is not something they will sign as airworthy without a look. That is not the FAA talking — that is the person whose certificate is on the line.
Why It Matters: Magneto failures are not always polite. A distributor block that arcs internally can take out the ignition on one side without warning, and a failed impulse coupling can shower the accessory case with metal. The 500-hour inspection exists because the wear items inside — points, condenser, carbon brush, distributor gear — are consumable parts, not lifetime parts.
Check your AD list too. Several older airworthiness directives touch magneto impulse couplings and specific Bendix and Slick part numbers, and those are mandatory with their own recurring intervals. Your logbooks should show which apply to your serial numbers.
Edge: Nobody wins on paper — but the inspection is recommended for everyone and may be mandatory when incorporated into an approved inspection or maintenance program, so treat it seriously even when operating under ordinary Part 91.
What Each Path Costs
Shop quotes vary by region and by whether the magneto stays on the aircraft, so treat the figures below as typical 2025–2026 general aviation pricing rather than a firm number for your airplane.
The 500-hour inspection is the cheap one. The magneto comes off, the shop or your A&P opens it, checks the points and contact assembly, condenser, distributor block and gear, coil, bearings and impulse coupling, replaces the consumables, then reinstalls and re-times it to the engine. Expect roughly $150 to $400 per magneto in parts and labor, and commonly $600 to $900 to do both sides of a four-cylinder single including removal, bench work and timing.
A magneto overhaul means the unit is fully disassembled, all wear parts replaced to new limits, tested on a bench and returned with a yellow tag and a new zero-time record. Slick overhauls typically run $450 to $800 each. Bendix-style S-20 and S-1200 series overhauls run higher, often $700 to $1,500 each, and the dual-magneto units found on some Lycoming engines land at the top of that band.
Replacement with a new or factory-rebuilt unit costs more up front. As of 2025, new Slick 4300 and 6300 series magnetos generally sell in the $1,000 to $1,600 range each depending on part number, and new or factory-rebuilt Continental S-1200 series units commonly run $1,500 to $3,000 each. Exchange programs, where you send your core back, trim a few hundred dollars off.
Do not forget the ignition harness. It ages on the same clock as the magneto, and a full harness replacement is usually $400 to $900 per engine. If the harness is original and you are already in there, doing it together saves a second round of labor.
Flying411 keeps aircraft listings, engine times and ownership cost guides in one place, so you can compare what a fresh top end and new ignition actually add to an asking price.
Edge: The 500-hour inspection, by a wide margin, on cost per hour of protection bought.
| Option | 500-Hour Inspection | Overhaul | New / Factory Rebuilt | Electronic Ignition (one side) |
| What happens | Disassemble, inspect, replace points, condenser, brush; re-time | Full teardown, all wear parts to new limits, bench test, yellow tag | Old unit removed and discarded or returned as core | Magneto removed, SureFly SIM installed under STC on the impulse-coupled side |
| Typical cost per unit (2025–26) | $150–$400 | Slick $450–$800; Bendix $700–$1,500 | Slick $1,000–$1,600; Continental S-1200 $1,500–$3,000 | Roughly $1,500–$2,000 plus installation |
| Shop time | Half a day to a day | Two days to two weeks unless you use exchange | Same-day once the part is on the shelf | Half a day to a day, plus paperwork |
| Record after the work | Logbook entry, hours continue to accumulate | Zero time since overhaul | Zero time since new | New STC'd appliance, Form 337 and flight manual supplement |
| Next scheduled event | Another 500 hours | 500-hour inspection, then overhaul near engine TBO | 500-hour inspection at 500 hours | Manufacturer states no 500-hour internal inspection |
| Power source | Self-generating | Self-generating | Self-generating | Needs ship's electrical power |
| Best for | Magnetos in known condition, under about 1,000 hours | Bendix-style units, engines mid-life | Slick owners, and anyone at engine overhaul | Owners wanting easier starts and variable timing |
Reliability, Downtime and What Actually Fails
Magnetos fail in a small number of predictable ways. The distributor block cracks or carbon-tracks, which shows up as a rough mag check or an erratic drop. The points burn or drift out of tolerance, which shifts internal timing. The coil breaks down, often when hot. The impulse coupling — the spring-loaded device that gives you a hot spark at cranking speed — wears at the pawls and flyweights. And in aircraft that sit, moisture gets in and corrodes everything.
That last one deserves attention. An airplane that flies 40 hours a year will reach 500 hours in more than a decade, and calendar time punishes a magneto as hard as flight time does. Shops that open up a low-hour, long-idle magneto routinely find corrosion on the cam and rust on the bearings. If your airplane sits, inspect on the calendar, not the tach.
Keep in Mind: A magneto drop within limits on the runup does not mean the magneto is healthy. It means it is firing. Internal timing drift, a marginal coil and early distributor tracking can all hide behind a perfectly normal 100 RPM drop.
On downtime, replacement wins. A shop with the right part number on the shelf can have you flying the same afternoon. An overhaul means your magneto goes away, unless you use an exchange program where a yellow-tagged unit ships out and your core goes back. Straight overhaul with your own unit can idle the airplane for a week or two at a busy shop.
Our broader aircraft engine inspection guide covers how this fits with the rest of the scheduled work, and the 50-hour Lycoming inspection article explains the shorter-interval items that catch problems between magneto services.
Edge: New or exchange replacement, for downtime; a draw on reliability, since an overhauled unit and a new one both leave with zero time.
The Electronic Ignition Wild Card
The SureFly SIM is an STC'd electronic ignition module that bolts into a magneto pad and replaces one magneto — normally the impulse-coupled side — while the other magneto stays put. It has no points, no distributor block and no impulse coupling, and the manufacturer says it requires no 500-hour internal inspection. It also varies ignition timing with manifold pressure, which SureFly says improves starting and trims fuel burn slightly at altitude.
The trade-off is straightforward: a magneto makes its own electricity and a SIM does not. It runs off ship's power. For many owners that is a non-issue, and keeping one traditional magneto on the other side is exactly why the STC is written the way it is. But it is a real difference in how your ignition behaves, and it is worth thinking about before you spend the money.
Price-wise, a SIM costs roughly what a new Bendix magneto costs, plus installation and paperwork. The savings show up over the next decade in inspections you no longer perform on that side.
Good to Know: Approval is by engine and airframe model. Check the SureFly approved model list against your exact engine designation before ordering, and confirm the installation gets a Form 337 and a flight manual supplement in the records — a buyer's pre-purchase inspector will look for both.
Edge: Electronic ignition, on long-run maintenance cost; traditional magnetos, on simplicity and independence from the electrical system.
Which One Should You Buy?
The 300-hour-a-year owner with mid-time Slicks. Do the 500-hour inspection on schedule and budget for new Slicks at engine overhaul. At Slick prices, a full overhaul on a high-time unit rarely beats a new one by enough to justify the extra downtime. Champion designed these to be affordable enough to swap.
The weekend flyer whose airplane sits. Do not wait for 500 flight hours to think about age. Long calendar time can produce internal corrosion even at low hours, and Slick maintenance guidance also includes a calendar-based overhaul recommendation. Use the current manufacturer guidance for the exact magneto rather than inventing a four- or five-year inspection interval.
The owner facing engine overhaul. Deal with the ignition as part of the whole package. New or overhauled magnetos plus a new harness alongside a fresh engine is the cleanest logbook story and the easiest thing to explain to a future buyer. Our guides on when to overhaul an aircraft engine and Lycoming rebuilt versus overhaul cover how the accessories fit into that decision.
The owner with Bendix S-1200s. Overhaul. These are substantial, expensive units built to be rebuilt many times, and a shop overhaul with a yellow tag costs meaningfully less than factory new.
Flying411 keeps maintenance explainers and operating cost breakdowns in one place, so you can compare what a fresh ignition system means against the rest of an aircraft's annual bill.
Pro Tip: When the magnetos come off, have the shop record the internal timing it found before touching anything, not just the timing it set. Drift from spec tells you whether the unit is wearing normally or heading for trouble, and that note is worth money at resale.
Building It Into Your Reserve Instead of Your Surprise Fund
The smart way to handle the magneto 500-hour inspection is the same way you handle the engine and the propeller: set money aside per flight hour so the bill is already funded when it arrives. At $600 to $900 a pair every 500 hours, that is roughly $1.20 to $1.80 per hour for the inspections alone, and maybe another $3 to $5 per hour if you are sinking funds toward eventual replacement. Our guide on how much to set aside per flight hour and the walkthrough on calculating operating cost per hour show where this line item sits among everything else.
If you are buying rather than owning, ask for the magneto hours and the date of the last 500-hour inspection during the pre-purchase. Two identical airplanes can be $2,500 apart in deferred ignition work, and it will not show anywhere on the spec sheet.
Flying411 keeps aircraft for sale, engine data and owner cost guides in one place, so you can compare two candidates on what they will actually cost you, not just the asking price.
When you are ready to compare listings, visitFlying411and see what is on the market today.
Frequently Asked Questions
Is the 500-hour magneto inspection an FAA requirement?
Not for most Part 91 owners. It comes from manufacturer maintenance guidance rather than a general FAA rule — Champion recommends 500-hour inspections for non-pressurized Slick magnetos, while Continental publishes comparable inspection guidance for its Bendix-design units. Your mechanic signs off work under 14 CFR Section 43.13, which requires using the current manufacturer's maintenance manual or Instructions for Continued Airworthiness, or other methods, techniques and practices acceptable to the FAA.
How long do aircraft magnetos actually last?
With the 500-hour inspections done, many magnetos reach engine TBO — commonly 1,800 to 2,000 hours on typical Lycoming and Continental piston engines — before needing overhaul or replacement. Aircraft that sit for long periods often need work much sooner because of internal corrosion.
Can my A&P do the inspection, or does it need a specialty shop?
An A&P can perform the 500-hour inspection with the correct manufacturer manual, tooling and timing equipment. A full overhaul requires a certificated repair station with bench test capability, because the unit has to be run and tested before it can be yellow-tagged.
Is it worth overhauling a Slick magneto?
Often not. A Slick overhaul at $450 to $800 competes with a new unit at $1,000 to $1,600, and the new one comes with zero time and no core hassle. Bendix-style magnetos are a different story — their higher new price makes overhaul the sensible route.
