Decision Time: Questioning Magnetos

Traditional magnetos are among the last purely mechanical systems still hanging on in piston aircraft. For decades, the decision at inspection time was simple: open them up, spend the money, and move on. That equation has changed. With multiple electronic ignition STCs now available for certified aircraft—and more in development—owners are increasingly faced with real choices at the 500-hour mark, each carrying different costs, complexity, and long-term implications.

My Cessna T310R is equipped with Bendix-style magnetos, which have been extremely reliable over the last 400 hours. But the next 500-hour inspection interval is approaching quickly, forcing a decision sooner rather than later. Plus, owning and maintaining a twin adds another layer of complexity. I’m dealing with four magnetos and four ignition harnesses. While a magneto inspection or overhaul is relatively “aviation cheap” from a labor standpoint, this is the natural inflection point: Continue operating a legacy system, or step into electronic ignition.

Mag Timing: Turbos Are Different

Electronic ignition systems offer variable timing on many normally aspirated engines, allowing ignition advance to increase as power is reduced and altitude increases. That capability—approved on many normally aspirated installations—is where much of the advertised efficiency gain comes from, primarily through improved fuel efficiency.

Turbocharged engines, however, operate under very different constraints. Because they maintain high manifold pressures—even at altitude—cylinder pressures remain elevated across much of the operating envelope. That significantly reduces detonation margin, making aggressive ignition timing advance unsafe. A turbocharged engine at 15,000 feet maintaining 30 inches of manifold pressure is operating under cylinder pressures similar to a normally aspirated engine at full power—conditions where excessive timing advance can quickly lead to destructive detonation.

For this reason, electronic ignition STCs for turbocharged engines tightly constrain timing authority. SureFly with its drop-in electronic mags limits turbocharged installations to fixed timing only, effectively mirroring traditional magneto timing throughout normal operation. ElectroAir with its electronic ignition systems, by contrast, does allow ignition advance on turbocharged engines—but only within conservative, STC-approved schedules that sharply limit advance at higher manifold pressures to preserve safe detonation margins.

The practical result is that turbocharged aircraft typically generally see far less dramatic efficiency gains from electronic ignition than normally aspirated engines. Any timing advance is modest and confined to lower-power operating regimes rather than applied broadly across climb and cruise.

Still, that doesn’t make electronic ignition a poor choice for turbocharged aircraft. Benefits such as improved starting, smoother combustion, more consistent spark energy, and reduced maintenance remain compelling. But the significant timing optimization—and corresponding fuel savings—often advertised for normally aspirated engines simply isn’t available to the same extent on turbocharged installations.

Magneto Inspection and Overhaul

For most owners, the 500-hour magneto interval has become a de facto overhaul decision point. While the underlying drivers vary by magneto type—ranging from manufacturer guidance to AD compliance—many shops and owners treat the 500-hour mark as the practical time to open the magnetos and address wear. From a logistics standpoint, magneto inspections fit neatly into an annual or other planned downtime. Several reputable shops across the country offer the service, some on an exchange basis and others quoting turn times of two to three weeks.

For my airplane, Poplar Grove Airmotive quoted $525 per magneto plus parts. That puts the fixed inspection cost at $2,100, and budgeting roughly $900 for parts brings the total to about $3,000, plus a few hours of labor to reinstall—all to buy another 500 hours of service life.

The most frustrating part isn’t the cost—it’s disturbing a system that has been working flawlessly. Reinstalling and re-timing magnetos on a twin is straightforward, but tedious, and anytime a reliable component is opened up, there’s always a risk that something won’t go back together quite as smoothly as it came apart. There are alternatives.

SureFly SIM

The SureFly Ignition Module (SIM) is probably the most familiar electronic magneto replacement on the market today. It’s designed as a form-factor replacement for a traditional magneto and is approved for both four- and six-cylinder engines. The SIM uses solid-state electronics with minimal internal moving parts, eliminating the traditional wear items that drive 500-hour inspections. SureFly states the SIM has a 2,400-hour service life, after which it must be returned to the factory for evaluation rather than overhauled in the field.

The system provides a consistent spark, advertised improved starting, modest weight savings compared to a Bendix magneto, and—on normally aspirated engines—variable timing. On turbocharged aircraft like mine, variable timing is not part of the approval basis, but the other benefits remain relevant. Pricing runs roughly $2,095 for four-cylinder and $2,295 for six-cylinder SIMs. However, switching from Bendix magnetos requires a Slick-style ignition harness, adding roughly $935 per harness.

While the FAA does allow dual electronic ignition installations, the requirements escalate quickly unless the aircraft already has fully independent electrical systems. Adding a second SIM per engine typically requires a dedicated backup battery, additional wiring, switches, and added labor. A 24-volt backup battery alone costs about $2,093.

For my airplane, replacing all four magnetos with SIMs—including new ignition harnesses and backup batteries—would push the parts cost north of $17,000 before labor. Realistically, if I went the SureFly route, I’d replace only two magnetos with SIMs and overhaul the remaining Bendix units, bringing the total parts cost to roughly $8,000 before labor.

ElectroAir

The system I’ve spent the least time considering is ElectroAir. Unlike SureFly, ElectroAir is not a magneto-shaped replacement—it’s a true electronic ignition system with external components, sensors, wiring, and control modules. My aircraft would use the EIS-6100-T1M, priced at $4,560 for a single-magneto replacement. That price includes all required components, but installation time is significantly longer than a drop-in solution.

The biggest drawback, in my view, is shop familiarity. Owner reports tend to be very positive when installations are performed by experienced or authorized shops, but mixed when installed by mechanics unfamiliar with the system. Several owners I talked with ultimately removed the system due to troubleshooting challenges. But again, the key is to take the installation to a shop that has done plenty of installations. ElectroAir can help with finding a qualified shop.

Replacing two magnetos with ElectroAir and overhauling the remaining two would put the parts cost just under $11,000 before labor. It’s a viable option—but one that depends heavily on installer expertise.

Champion Lightning Series Magneto (LSM)

At AirVenture 2024, Champion Aerospace unveiled its Lightning Series Magneto (LSM), and it’s the product I’m most excited about. The LSM is a self-powered electronic magneto capable of generating spark at roughly 100 rpm, with no impulse coupling, no breaker points, and no external electrical power required. If the starter can spin the engine, the magneto can run it.

Champion is positioning the LSM as a true drop-in replacement designed to last the full engine TBO with no scheduled maintenance. Based on discussions at Oshkosh and subsequent reporting, Champion is targeting market availability in late 2026, with four-cylinder versions first and six-cylinder options to follow. There’s no published pricing yet, but costs are expected to be similar to SureFly. If the FAA allows dual LSM installations without backup batteries, the system could significantly reduce cost and complexity compared to existing electronic options.

Decision Time

After talking with maintenance providers, reading owner reports, and weighing costs, I remain impressed by the SureFly SIM as a product. However, communication with the company over the past year—despite multiple attempts to arrange a field report—has been difficult. While the documentation is thorough and the product well regarded, limited engagement raises reasonable questions about long-term customer support.

The Champion LSM, by contrast, has the potential to be a true game-changer. A self-powered electronic magneto with no external dependencies could finally deliver the simplicity owners want without the electrical complexity that currently drives costs up. Unfortunately, magneto clocks don’t stop for future products.

With my 500-hour interval approaching, I’ll be sending all four Bendix magnetos out for inspection and overhaul and buying another service cycle—while waiting, somewhat impatiently, for Champion’s LSM to reach the market.