Gyro Repairs: Price EFIS, First

For years and years we’ve been talking about the benefits of solid-state flight instrument upgrades, yet there are still plenty of panels sporting spinning iron gyros. Eventually, they’ll need to be repaired or overhauled. If a major avionics upgrade isn’t in the budget, it’s tempting to pull the trigger on a gyro exchange and that’s not always a bad idea, but depending on the gyro, that could be throwing good money after bad. In most cases, there is a solid argument for sending spinning gyros to the rubbish bin and removing the unreliable and weight-adding vacuum system at the same time. Here’s some advice on how you might approach the decision, which should always include getting a quote for a budget EFIS.

Autopilot Critical

What a lot of owners fail to understand is that many gyros are actually part of the autopilot system. In a rate-based autopilot, it’s the electric turn coordinator that sends a roll signal (tach voltage) to the autopilot as the primary roll-axis reference. Two examples include most analog S-TEC autopilots and also the BendixKing KAP140. There are more OEM attitude-based autopilots, though, and these legacy systems rely on a spinning attitude gyro for precise roll and pitch signals. The King KFC150/200/225 series, many Century/Piper systems, and many Cessna/Sperry autopilots are attitude based. The attitude gyros that drive these systems are vacuum driven (and some have flight director command bars as added complexity) but have electronic pickoffs for the input reference signal.

Directional gyros (and HSIs) are generally more generic than attitude gyros, but for autopilots with heading command, they play an integral role in the autopilot’s function and performance. Notoriously, autopilot gyros have always been more expensive to replace and overhaul than plain-vanilla spinning gyros, and that usually drives the decision to step up to an EFIS. That’s because the majority of EFIS models—from Garmin GI 275s, TXi displays and the G3X Touch, to Aspen and Dynon PFDs—are all capable of driving legacy analog autopilots, though the Dynon HDX Certified system may be STC-limited.

In an autopilot interface with a traditional attitude gyro, consider that overhauling or repairing the gyro is only part of the expense that tags along. The shop might have to complete a setup/alignment procedure so the autopilot flies properly. This includes bank angle adjustments and command bar alignment. In the case of the analog King KFC series autopilots, this could mean several hours of additional shop labor on top of the effort to remove and replace the instrument. This is especially true if the gyro was exchanged with a different unit and the adjustments were set to null. With a solid-state EFIS doing the driving, it generally means setting it up once and forgetting it because these instruments might never be removed for service given their reliability and lifespan compared to gyroscopes. Think long term.

Know What You’re Getting

Especially if you leave it up to your maintenance or avionics shop to handle a gyro problem, know the difference between a repair and an overhaul. You might even want a price to compare the repair versus a full-up overhaul. If you have no intentions of ever upgrading out of the spinning gyro, it could make sense to invest in an overhaul while the instrument is out and on the bench. Consider that the majority of avionics shops outsource instrument work because they don’t have in-house capabilities to work on instruments. This means you’re relying on a third-party facility to work on your instrument. Ask about warranty.

In the world of gyro repairs, 90 days is generally the limit of major repairs, but some might be 30 days. For complete teardown overhauls, we’d want to see a one-year warranty in place, though six months is more common. Remember, you’re talking several thousands of dollars here, plus some downtime. Systems like the King KG102A remote electric gyro, King KI256 flight director gyro and even an old Century NSD360 or electric NSD1000 will be a big investment for a quality overhaul.

One shop that we’ve always recognized for high-quality work and good support is Mid-Continent Instruments and Avionics. The company has a good supply of replacement parts, but like many shops, might struggle to find parts for long-discontinued instruments. For that reason, not all gyros will be eligible for an overhaul because the shop simply can’t overhaul the unit by definition. Moreover, some gyros might be obsolete by part number and mod status, so these might not be worthy of an overhaul exchange. That means paying the outright price at a hefty premium.

Modern Tech at a Cost

For more basic vacuum-driven gyros, one option might be an electric replacement without going all in on an EFIS. The Mid-Continent Instruments and Avionics 3300-series electric DG is replacement for the AIM205 and RC Allen RCA215 units, as one example. But at $4680 for a new outright, we think it’s worth pricing something like Garmin’s GI 275. The EHSI version of this instrument has a list price of $4595 but will require a new installation. There’s also the uAvionix AV-30. It has a starting price of $2495 and it requires the $395 external magnetometer. For connecting an IFR GPS navigator for full EHSI capability, you’ll need the $799 AV-HSI. This is an external digital/analog converter.

Both the Garmin and uAvionix instruments are available in attitude instrument versions, but if your plans include replacing two spinning gyros (AI and DG), we think it makes sense to get a quote for a big-screen EFIS, too. But obviously that will require major panel work to accommodate the big display. Still, think in terms of what two gyro overhauls will cost, especially if you fly the airplane a lot of hours per year. “While I resisted a gee-whiz upgrade simply because my analog setup works for me, I finally got tired of overhauling my autopilot gyro every few years to the tune of almost $5000 total,” a hangar neighbor with a Beech Baron told us.

Using the King KI-256 flight director gyro as an example, the typical overhaul cost is around $3500, not counting labor and freight charges to send the unit out and get it back in. Accomplished twice in the span of, say, eight years, that could easily be an $8000-plus expense, or roughly the cost of dual Garmin GI 275 units.

And it’s worth mentioning to take any gyro troubleshooting to a shop that has experience doing it. Systems like the King KCS55A electric HSI with slaved compass system have multiple components. What could appear to be a remote heading gyro problem could be a variety of other issues. We’ve seen more than one sad story of owners spending thousands of dollars on shotgun gyro repairs only to find the problem was in the wiring or in another component. These days finding quality troubleshooting support for legacy analog systems isn’t as easy as it once was. The Aircraft Electronics Association is a good source for finding specialty shops. 

Wrap It Up

Face it, airplanes with old iron gyros will likely fetch less money during resale than ones that have been upgraded to solid-state gyros and big-screen glass. The investment generally pays off in the long run, rather than nursing old gyros that might be on borrowed time. Plus, you might find that adding a precision solid-state EFIS in place of an analog spinning gyro will inject some needed performance into an old autopilot. That in itself could be worth the upgrade.

We’re consistently hearing from shops that parts for old units are becoming scarce, and that means salvaging parts from several core units to make one good one. That’s not sustainable. Remember, some of these old gyros that work with analog autopilots are more than 45 years old—that might be incentive enough to send them to the rubbish bin forever in favor of solid-state replacements.