Dynon, the Approved Model List STC, and How the Experimental World Talked Its Way Into the Certified Cockpit

The single biggest safety and cost revolution in general aviation over the past two decades wasn’t a new airframe - it was the instrument panel. Dynon, a company that spent the early 2000s building affordable electronic instruments for homebuilders, ultimately earned an Approved Model List (AML) Supplemental Type Certificate - in partnership with the EAA - that made a modern, solid-state attitude indicator legal to install across a huge swath of the certified fleet. The result: aging Cessnas, Pipers, and Beechcraft can now fly behind safer, cheaper glass that costs a fraction of the traditional certified hardware it replaces.

What Changed in the General Aviation Cockpit

If you learned to fly in a 1970s Cessna or Piper, you learned on the “six pack” - six round dials for airspeed, attitude, altimeter, turn coordinator, heading, and vertical speed. Behind each was a mechanical marvel: spinning gyroscopes, aneroid capsules, and vacuum pumps drawing air across spinning wheels to hold your attitude indicator upright.

Every one of those instruments was expensive because every one was certified - signed off by the FAA for a specific part in a specific installation through a Supplemental Type Certificate (STC). That process costs manufacturers enormous money, and the cost lands squarely on the aircraft owner.

The consequence was a safety compromise we lived with for decades. A vacuum-driven attitude indicator - one of the most safety-critical instruments on board - could cost several thousand dollars to overhaul or replace, and it was still a spinning gyro that could tumble, fail slowly, and lie to you. Pilots have flown perfectly good airplanes into the ground in cloud behind a dying vacuum system, trusting an instrument that was quietly winding down.

Why the Experimental World Moved Faster

The experimental amateur-built category plays by different rules. If you build the airplane yourself - the RVs, Lancairs, and Sonexes of the world - the FAA does not require your instruments to be certified. The builder takes responsibility, and can put whatever they want in the panel.

That freedom created a market for companies willing to build genuinely modern electronics without the crushing cost of certification. Remove the certification tax, and innovation gets fast and cheap.

Dynon, based in the Seattle area, entered that market in the early 2000s with affordable electronic flight instruments for homebuilders. What they were doing technically is the heart of the story.

How a Solid-State Attitude Indicator Actually Works

Dynon replaced the old spinning-gyro attitude indicator with an Attitude and Heading Reference System (AHRS). Instead of a mechanical gyro, an AHRS uses solid-state sensors - tiny accelerometers and rate sensors etched into silicon chips. It’s the same basic technology family that senses when you rotate your phone or triggers your car’s airbag.

These are MEMS sensors - Micro Electro Mechanical Systems - microscopic mechanical structures built onto a chip. No spinning wheel, no vacuum pump, nothing to tumble. A computer takes the readings, blends them with a magnetometer for heading and a pressure sensor for altitude and airspeed, and computes your attitude mathematically hundreds of times per second.

Here’s the honest engineering. A single MEMS sensor is actually noisier and less stable than a good mechanical gyro over the short term. But you don’t use a single sensor - you use several, fuse the data with an algorithm, and cross-check against the other information the box already holds. Taken as a whole, the result is more reliable, has no moving parts to wear out, weighs a fraction of the old iron, and costs a small fraction of a certified gyro.

That is the entire story of modern avionics in one sentence: individually humbler parts, collectively far more robust, and radically cheaper.

By the 2010s, a homebuilder could sit behind a full glass panel - a bright synthetic horizon, moving map, and engine monitoring all on one screen. Dynon’s SkyView (later the SkyView HDX) and Garmin’s G3X put the experimental crowd behind panels nicer than what the airlines flew a generation earlier.

The Absurdity That AML STCs Finally Fixed

Picture two identical Cessna 172s parked side by side. One is registered experimental, exhibition category, with a gorgeous two-screen glass panel that cost a few thousand dollars. The other is a standard certified 172, legally required to keep flying behind a vacuum pump and a spinning gyro - because installing that same cheaper, better, safer box was illegal without an STC nobody had funded.

Same airplane. Same technology on the shelf. One pilot allowed to have it, one not - purely because of a piece of paper.

The breakthrough was the Approved Model List STC (AML STC). A normal STC is specific: approved for one part in one make and model. Installing equipment across twenty airplane models historically meant chasing approval for each one - expensive, slow, and impossible to justify for a 40-year-old trainer with thin margins.

The AML STC flips that. The manufacturer does the engineering work once, proves the installation is sound, and the FAA issues one STC carrying a long list of every airplane type it covers - Cessnas, Pipers, Beechcraft, dozens of legacy models on a single approval. Your mechanic confirms your airplane is on the list, installs per the instructions, and signs it off.

One approval, hundreds of airplane types. The certification cost spreads across the entire fleet instead of a single model, and the math finally works.

Why This Matters for Pilots

This didn’t happen in a vacuum. The FAA had signaled for years that it wanted life-saving equipment in older airplanes without the traditional cost - a policy shift often discussed under the agency’s non-required safety enhancing equipment guidance. The logic: if a piece of gear makes an airplane safer and isn’t required equipment, stop treating its approval like certifying a new airliner. Angle of attack indicators were an early beneficiary; attitude indicators were next.

Dynon walked through that door. In partnership with the EAA, it earned an AML STC for a certified version of its attitude indicator - a solid-state, MEMS-based electronic unit with its own internal backup battery - legal to install across a large portion of the certified fleet, at a launch price that shocked anyone who’d priced a traditional replacement.

The safety payoff is direct. That box carries its own backup battery, so if the electrical system quits, it keeps showing attitude - with no vacuum pump in the loop at all. For a pilot in an old Cessna who blunders into cloud, that’s the difference between a dead instrument spinning down and a rock-solid horizon that just keeps working. Garmin has since followed into the same certified-retrofit space, and the category keeps expanding from single instruments toward fuller certified glass retrofits.

The Caveats Worth Knowing

Cheaper does not mean free. The instrument may cost a fraction of the old iron, but you still pay for installation - a proper panel job by a qualified shop is real labor and real money. The revolution is in hardware price and the licensing model, not in making avionics a weekend impulse buy.

An AML STC is only as good as its list. Your specific airplane, serial-number range, and existing equipment all have to be covered. “It fits, so it’s legal” is not how this works - your mechanic and the STC paperwork make that call every time.

Solid-state does not mean immortal. These systems depend on software and sensor calibration; they get bugs, service bulletins, and firmware updates like anything with a processor. A MEMS AHRS is more reliable than a vacuum gyro across the fleet, but it represents a different failure mode, not the absence of failure. You still fly with a scan, you still cross-check, and you still know your backup and how to use it.

Finally, the bigger picture: there’s a lasting tension between the permissionless innovation of the experimental world and the careful, expensive rigor of certification. The experimental side moves fast and delivers cheap, brilliant gear; the certified side moves slow and delivers traceability and accountability. The AML STC story is what cooperation between those two worlds looks like - and that cooperation, more than any single gadget, is the real milestone.

Key Takeaways

• Dynon built affordable MEMS-based electronic flight instruments for the experimental market in the early 2000s, then earned a certified Approved Model List STC in partnership with the EAA.
• An AHRS replaces the spinning vacuum gyro with fused solid-state sensors - no moving parts, no vacuum pump, lighter, and far cheaper.
• The AML STC lets a manufacturer certify one installation across hundreds of legacy airplane models, spreading cost across the fleet and making retrofits affordable.
• The certified Dynon attitude indicator includes an internal backup battery, keeping attitude available even in a total electrical failure.
• Solid-state avionics are more reliable across the fleet but still require pilot discipline: maintain your scan, cross-check, and know your backups - and confirm your exact aircraft is on the STC’s approved list before installing.