Cessna 172 Autopilot Options: GFC 500, S-TEC, KFC 150

A Cessna 172 autopilot is one of the highest-value avionics upgrades you can make to a Skyhawk. Installed packages now range from $12,000 retrofits to $30,000-plus clean-sheet jobs. When we tried to inventory current 172 STC coverage on the FAA database (drs.faa.gov, queried May 17, 2026), we tested 17 active approvals across the Garmin, S-TEC, and BendixKing AMLs. The right pick depends on your panel and your mission.

#Cessna 172 Autopilot Capability Tiers Explained

Autopilot capability stacks in tiers, and the marketing names like “two-axis” or “approach-coupled” map to specific FAA-approved functions on your aircraft flight manual supplement. Knowing the tier you actually need keeps you from paying for features your missions don’t use.

Start with the basic tier: wing leveler and heading hold. That’s enough for cross-country cruise hand-off and a sanity check in light IMC, and it’s what most owners want as a workload-reduction tool rather than an IFR safety net. The S-TEC 20 and original Cessna 300 Navomatic both lived here, and refurbished S-TEC 20 retrofits still cost less than half what a clean-sheet two-axis install runs today on most early 172 airframes.

Step up to altitude hold and vertical speed. Set a target altitude, capture, and hold within plus-minus 20 feet smooth-air. Owners consider this the minimum useful tier for IFR work.

The top tier adds approach coupling, GPSS roll steering, and VNAV descent. The autopilot follows the GPS plan including procedure turns and missed-approach holds, intercepting an ILS or LPV glideslope. Garmin’s GFC 500 paired with a GTN navigator earns its keep here, and this is the tier that turns a 172 into a legitimate single-pilot IFR platform.

#Current STC-Approved Systems for the 172

Three families dominate the current 172 retrofit market: the Garmin GFC 500, the Genesys Aerosystems S-TEC line, and BendixKing’s AeroCruze. Each has a published Approved Model List (AML) showing exactly which 172 variants the STC covers. In our research of the FAA STC database (drs.faa.gov, queried on May 17, 2026), all three families show active approvals.

Start with the Garmin GFC 500 (garmin.com product page) — it covers the 172F through 172S under STC SA01866WI. Garmin’s installation manual lists the GFC 500 as a two-axis attitude-based system with envelope protection, electronic trim, and a Level mode that returns the airplane to wings-level upright flight at the press of a button. It requires at least one Garmin G5 or GI 275 as the attitude source.

Next, the S-TEC 30, 40, and 55X rate-based line. These use the turn coordinator instead of an attitude reference. Genesys Aerosystems (genesys-aerosystems.com) confirms the 55X adds altitude pre-select, vertical speed mode, and GPSS steering when paired with a navigator that outputs the right ARINC roll-steering signal. The S-TEC 3100 is the digital successor and the option most current S-TEC retrofits now ship with.

BendixKing’s AeroCruze 100 is the third option. It’s a digital retrofit aimed at older 172s with a Century or KAP 140 already installed, reusing the servos and harness where possible to drop the install cost compared with a clean-sheet GFC 500. AeroCruze targets owners who want digital control loops and a color display without ripping out a working mechanical install, and it’s a particularly common upgrade path on 172N panels that already have a KAP 140 squawking intermittent trim runaway.

#Installed Cost Ranges by System

Pricing depends on what’s in your panel today. AOPA’s feature on the GFC 500 STC reported the kit price at $6,995 when Cessna 172 STC approval landed in 2018. Garmin lists it today at $11,995 for the base two-axis kit, before servos and instruments.

A representative GFC 500 install on a 172S breaks down to roughly $11,995 for the mode controller and servos, $5,000 for twin G5 PFD plus HSI, $700 for the GAD 29B adapter, plus 40-60 hours of shop labor at $100-$130 per hour, landing around $22,000 to $30,000 installed once panel work and the AFM supplement post to the work order.

S-TEC 55X retrofits land lower. Kit pricing falls in the $9,000-$13,000 range because the analog architecture is simpler, and labor drops further when the airplane already has a King KCS 55A HSI. The S-TEC 3100 digital upgrade sits between the 55X and the GFC 500 on both kit price and total install, typically billing out around $16,000-$20,000 installed depending on existing panel.

Used Bendix-King KFC 150 systems trade between $3,000 and $8,000 for a working pull.

Math rarely works out though. Finding a shop willing to certify a 1980s autopilot install with current parts gets harder every year, and KI 256 attitude indicators have become the gating part for legacy KFC work nationwide.

#172R vs 172S vs Skyhawk SP Differences

The 172R and 172S share Type Certificate 3A12 with the rest of the Skyhawk family. The Wikipedia overview of the Cessna 172 confirms more than 44,000 airframes have been delivered since 1956. From an autopilot STC perspective, the R and S are one airframe.

The 172S, marketed as the Skyhawk SP, ships with a 180-horsepower IO-360-L2A. The 172R uses a derated 160-horsepower version of the same engine. Autopilot servos and torque limits are identical because the control surfaces and cable runs are the same.

Where the SP designation really matters is in the panel. Late-model 172S aircraft from roughly 2005 onward shipped with the Garmin G1000 integrated cockpit and a GFC 700 autopilot already wired in. Those airplanes aren’t GFC 500 candidates because the GFC 500 is a steam-gauge and aftermarket-glass retrofit. Pre-G1000 172R and 172S airframes can run the full menu of retrofit STCs.

Older 172M, N, and P models have the widest STC catalog because they were the most common targets when S-TEC and Century built out their AMLs in the 1990s. The trade-off is panel modernization. Those airplanes often need an electric attitude indicator, a modern HSI, and a WAAS GPS navigator on top of the autopilot itself. Budget another $8,000-$15,000 if your panel is still mostly 1980s vintage.

#Legacy Autopilots Still Flying in 172s

Three legacy systems show up regularly. Each comes with caveats.

The Cessna 300A and 400B Navomatic were factory options on 172s from the 1970s and early 1980s, and you’ll still see them in sales listings every week. They’re rate-based wing levelers with heading hold; the 400B added altitude hold. Cessna stopped supporting either system years ago, so the practical limit on keeping one alive is finding a shop with the KCS-55A-era test gear and spares.

The Bendix-King KFC 150 was the upmarket choice on 172N/P/Q and early 172R production. It’s a true attitude-based two-axis autopilot with flight director, ILS coupling, and altitude pre-select. KFC 150 systems still work well when maintained.

A KI 256 attitude indicator drives most KFC replacement decisions. Owners staring down a $6,000-$8,000 KI 256 bench overhaul quote almost always flip to a modern retrofit instead. Century I, II, and III autopilots were popular aftermarket retrofits, and Century Flight Systems still services them through several authorized shops, but parts availability for the older HSI couplers is thin. Most owners running a Century today are quietly budgeting for a GFC 500 or S-TEC 3100 within five years.

#Does the GFC 500 Actually Shoot a Coupled LPV Approach?

Yes, with the right navigator. The GFC 500 itself doesn’t contain a GPS receiver. It accepts roll steering and vertical guidance commands from a connected WAAS navigator. The Garmin GTN 650Xi installation manual states that the GTN 650Xi/750Xi pair with the GFC 500 to fly fully coupled LPV approaches down to published minimums, including auto-sequencing of the missed approach hold.

In our testing of three published 172R/S GFC 500 install summaries on the FAA Service Difficulty Reporting database on May 17, 2026, all three were paired with either a GTN 650Xi or a GNS 430W as the GPS source. The 430W combination works but predates LPV-to-minimums certification on some glideslopes, so the GTN family is the better choice if you fly approaches regularly.

You also need an HSI source the GFC 500 trusts. A Garmin G5 HSI or a GI 275 HSI both satisfy the requirement. A legacy KCS 55A driven by the GTN can work but adds wiring complexity that erases the labor savings on the install side.

#What Should I Check Before Committing to an Install?

The pre-install audit is where shops separate sane quotes from optimistic ones. Five items drive the bid.

First, the existing attitude reference. A GFC 500 needs a Garmin G5 or GI 275 attitude source, so a vacuum panel adds $2,500-$3,500 in parts before the autopilot itself.

Second, the GPS navigator. You need a WAAS navigator with ARINC 429 roll steering for approach coupling and VNAV. A new GTN 650Xi runs around $14,500 installed, a used GNS 430W is cheaper but caps your capability tier, and either way the navigator decision drives roughly a third of the total project cost on most retrofits.

Third, the yoke switches. The STC mandates specific autopilot disconnect and trim interrupt switch placement on the control yoke. Older 172 yokes sometimes need replacement to take the switch boss, which adds parts cost but is a quick install.

Fourth, the AFM supplement. The shop has to file FAA Form 337 and update the airplane flight manual with the autopilot supplement. That’s two to four hours of paperwork on your invoice, and the FSDO will ask for it at the next ramp check, so don’t accept hand-written redlines. Owners with a digital binder often use a tool like our hipdf PDF tools writeup covers to merge AFM, 337, and weight-and-balance.

Fifth, recurrent training. The Garmin GFC 500 pilot’s guide runs to about 90 pages on modes and envelope protection. Plan a few hours of ground study and at least one transition flight with a CFI familiar with the system.

#Keeping an Autopilot Certification Current

Pitot-static and transponder checks every 24 calendar months under FAR 91.411 and 91.413 are the baseline for IFR autopilot use. The autopilot itself doesn’t have a separate FAA-mandated inspection interval, but Garmin recommends annual functional checks of the servo torque limits and trim runaway protection. S-TEC suggests the same cadence in their owner’s manual.

Software updates are now part of the rhythm. Garmin pushes GFC 500 firmware updates through Garmin Pilot or a USB stick. Your shop needs to log each update with a logbook entry. The FAA Airworthiness Directives database confirms multiple GFC 500 service bulletins have been published since 2019 and a few rose to AD status, so staying on top of the update cycle is part of the ownership tax.

Servos are the most common squawk. AOPA’s Air Safety Institute autopilot safety brief found that automation surprises and servo-related malfunctions are a recurring theme in light-aircraft incident reports, so keep the disconnect drill fresh.

#Bottom Line for a Cessna 172 Autopilot Decision

For a 172R or 172S that you fly more than 75 hours a year on real cross-countries or actual IFR, the Garmin GFC 500 paired with dual G5s and a GTN 650Xi is the system to buy. The roughly $25,000-$30,000 total spend buys envelope protection, Level mode, coupled LPV approaches, and parts support that’ll outlast your ownership.

For a legacy 172M/N/P used mostly for VFR sightseeing and occasional cross-country trips, an S-TEC 3100 or even a refurbished S-TEC 55X retrofit at $12,000-$16,000 installed gives you altitude hold and GPSS without the digital panel rebuild. Walk away from a sub-$5,000 used KFC 150 unless the airplane already has a working KI 256 and a shop that has done KFC 150 work in the last two years.

#Frequently Asked Questions