The Synthetic Vision System, the GPS Terrain Database That Renders a Three-Dimensional World on Your Primary Flight Display, and Why the Picture Is Only as Accurate as the Data Beneath It

Synthetic vision systems display a three-dimensional terrain picture on your primary flight display by combining GPS position with a stored elevation database. There is no forward-looking sensor involved - no radar, no lidar, nothing actively scanning the terrain ahead. The accuracy of everything you see depends entirely on the quality, currency, and completeness of the data stored in that database.

How Synthetic Vision Actually Works

The core mechanism is straightforward: your GPS receiver computes your position, your air data computer supplies altitude, and the SVS processor queries a stored terrain elevation database to render a computed projection of the terrain around you. The world on your screen is calculated, not sensed.

This distinction matters more than any other single fact about the technology. The picture looks like a window. It is not a window. It is a model built from data collected at a point in time, projected onto your display using real-time position and attitude inputs.

A Brief History: From Highway in the Sky to Glass Panels

The concept of rendering computed terrain on a flight display dates to at least the mid-1990s, when NASA Langley was running simulation research on a “highway in the sky” - a three-dimensional tunnel displayed on the PFD that reduced navigation to a tracking exercise. That concept never became standard equipment, but it fed directly into what synthetic vision became.

Chelton Flight Systems was building early implementations into experimental aircraft in the late 1990s. Their Flight Logic system gave experimental builders synthetic terrain capability before the certified world had anything comparable. The homebuilt community served as the proving ground.

The technology entered mainstream aviation when Garmin integrated SVS into the G1000 Integrated Flight Deck. The first production Cessna 172 and 182 deliveries with the G1000 in the mid-2000s brought synthetic vision into standard flight training. Today it is standard equipment across Garmin’s G1000, G3000, G5000, and G3X suites, the Avidyne IFD550, Dynon SkyView, and Universal Avionics InSight - ubiquitous across everything from experimental Light Sport aircraft to midsize turboprops.

Where the Terrain Data Comes From

The elevation data underlying most aviation SVS implementations comes primarily from the Shuttle Radar Topography Mission (SRTM). In February 2000, the Space Shuttle Endeavour flew an 11-day mission using dual radar antennas to map approximately 80 percent of Earth’s land surface. Horizontal resolution is 90 meters for most of the world and 30 meters in the United States.

That is the backbone of the terrain picture on your PFD. When your Garmin renders a mountain range on the display, the shape of those peaks comes from radar data collected from orbit a quarter century ago. That data has been validated and supplemented by avionics database companies including Jeppesen and Garmin’s own data team, but the foundation is a shuttle mission.

What the Obstacle Database Can and Cannot Show

Layered on top of terrain data is the obstacle file. The FAA’s Digital Obstacle File catalogs man-made structures over 200 feet above ground level - cell towers, antenna farms, wind turbines, power line structures, broadcast towers. When an obstacle appears on your synthetic vision display, it is because that specific structure has been reported, surveyed, and logged in that database.

The word logged is the operative one. The obstacle file contains structures that have been cataloged. It does not contain every structure that exists.

New construction is the persistent gap. A wind farm that broke ground eight months ago may not appear in your current database cycle. A temporary tower erected for broadcast or construction may never be formally logged at all. Any structure below the 200-foot reporting threshold is invisible to the system regardless of the hazard it presents on approach. The picture can show a clean, open valley while an unlisted tower sits invisible in that valley.

FAA Advisory Circular 23.1392, which governs SVS in general aviation aircraft, addresses this directly. The AC acknowledges that terrain and obstacle databases are not complete representations of the actual obstacle environment. It requires a current database for IFR operations and explicitly notes that currency does not equal completeness. This is not a defect - it is an inherent characteristic of any database-driven system modeling a world that changes continuously.

Synthetic Vision vs. TAWS: Two Different Tools

These technologies are related but distinct, and the difference matters.

TAWS (Terrain Awareness and Warning System) is a reactive alerting system. It monitors flight path parameters - closure rate to terrain, descent rate below minimums - and generates an alert when those parameters indicate a threat. Early Ground Proximity Warning Systems (GPWS) operated this way. Enhanced GPWS added a predictive look-ahead component using GPS and terrain databases, warning of terrain ahead before closure rates triggered a reactive alert.

Synthetic vision is primarily a display system. It takes the same terrain database and renders it visually, providing continuous situational awareness rather than a warning that fires only when something is about to go wrong.

Modern avionics typically integrate both. The SVS renders the terrain picture continuously; the terrain alerting system monitors flight parameters and generates audio warnings when thresholds are exceeded. They draw on the same database but serve fundamentally different functions.

GPS Integrity: When the Position Source Fails

Synthetic vision depends on GPS for position. The accuracy of the terrain picture is only as good as the position fix feeding it. With WAAS (Wide Area Augmentation System), modern GPS receivers deliver position accuracy of under 3 meters vertically across most of the continental United States - more than sufficient for accurate terrain rendering.

GPS is a radio frequency system, and radio frequency systems can be jammed or spoofed.

Jamming degrades the GPS signal until the receiver cannot compute a valid position fix. When that happens, your SVS will typically display a warning flag and the terrain picture becomes unavailable or unreliable. That is the receiver working correctly.

Spoofing is the more serious threat. A GPS spoofer feeds false position signals to your receiver, causing it to compute an incorrect position while believing the fix is valid. If your receiver is spoofed, your synthetic terrain picture shows the terrain at the false position, not your actual position. The picture will look completely normal.

GPS jamming and spoofing incidents have increased significantly in certain regions in recent years. The FAA and international aviation authorities have issued multiple NOTAMs documenting GPS unreliability near active conflict zones and certain border areas. This is not a reason to distrust synthetic vision in normal operations. It is a reason to maintain an independent navigation cross-check, particularly when operating in regions with documented GPS vulnerability.

AHRS Failure and the Picture That Lies

The synthetic terrain picture is rendered on top of an attitude reference derived from your AHRS (Attitude and Heading Reference System) - the microelectromechanical gyro and accelerometer package that tells your avionics what attitude your aircraft is in.

If your AHRS begins reporting incorrect attitude, your synthetic terrain picture shifts to reflect that incorrect attitude. The terrain rendering is not independent of your attitude source.

This is precisely why backup attitude indicators remain a certification requirement in glass cockpit aircraft with SVS installed. If your synthetic terrain picture shows wings-level while your backup AI shows a 10-degree bank, you have an AHRS problem. You fly the backup. The NTSB database contains documented cases of SVS cockpits displaying terrain information inconsistent with actual aircraft position due to GPS anomalies or sensor faults. The contributing factor in those cases is consistent: the pilot had reduced or abandoned the independent instrument cross-check that would have caught the discrepancy.

Automation Complacency and the Instrument Scan

Human factors researchers call the broader pattern automation complacency. When a system is convincing and intuitive, the brain’s error-detection function tends to relax. The SVS picture is specifically designed to be intuitive - it engages the visual system the way a window does. That engagement can pull attention away from altitude, airspeed, and the instrument scan.

NASA Langley human factors studies in the early 2000s documented this effect in simulation trials. Pilots flying with SVS sometimes shifted from an active instrument scan to prolonged visual fixation on the synthetic terrain picture, treating it as the primary reference rather than a supplement to the instruments. The pattern appeared consistently across different pilot experience levels.

The NASA Aviation Safety Reporting System (ASRS) - where pilots can voluntarily report close calls without enforcement action - contains multiple reports of pilots catching themselves flying primarily by the SVS picture rather than the instruments. In most cases, the pilot recognized it and corrected before anything went wrong. But the reports reveal a real behavioral tendency worth understanding before you are in the left seat at night in IMC.

Garmin, Avidyne, and other manufacturers design against this tendency. The synthetic horizon aligns closely with the attitude indicator. Terrain alerts use audio cues designed to break visual fixation. The philosophy is that the picture supplements the scan, not replaces it.

The Safety Record: What the Data Actually Shows

The safety data on synthetic vision is genuinely encouraging, and that deserves full weight.

Controlled flight into terrain (CFIT) was one of the dominant fatal accident categories in general aviation through the 1980s and 1990s. The introduction of GPWS reduced CFIT events significantly in airline operations. Enhanced GPWS added predictive capability. SVS added the three-dimensional rendering layer. Each technology built on what came before.

Studies from the AOPA Air Safety Institute and FAA accident review programs have documented continued downward trends in CFIT events in the SVS-equipped fleet. The technology works. The number of CFIT accidents in aircraft with modern avionics suites is lower than it was before those suites existed.

What FAA Certification Requires

Before AC 23.1392, there was no clear framework for approving SVS in type-certificated aircraft. Garmin and the FAA worked through several years of regulatory development to define the requirements that now govern every certified SVS installation.

The key requirements produced by that process:

• The terrain and obstacle database must be current for IFR operations
• The system must annunciate database currency status to the pilot
• Backup attitude indication independent of the AHRS must be available
• The synthetic terrain picture must be clearly distinguishable from actual outside visual conditions

These are not bureaucratic checkboxes. They are lessons encoded from the design process.

Where Synthetic Vision Is Heading

The industry is working toward integrating SVS with real-time data sources - merging ADS-B traffic, convective weather, actual cloud bases, and terrain into a unified situational awareness picture on a single display. The goal is a PFD that knows not just where the mountains are, but where the weather is building and where the other traffic is, all rendered in context against the terrain picture.

Higher-resolution terrain data is also coming. The difference between 90-meter and 30-meter resolution is significant in mountainous terrain where ridge lines matter at precision approach altitudes. As avionics storage and processing capacity grows, that resolution ceiling will continue to rise.

Research into fusing terrain databases with real-time satellite imagery is in early stages. The concept would allow SVS to reflect current ground conditions - new construction, terrain changes from wildfire or erosion, updated runway configurations - without waiting for traditional database update cycles. The technology to support this in a certified avionics context is not yet mature, but the problem is being worked.

Key Takeaways

• Synthetic vision is database-driven, not sensor-driven. No radar or lidar is scanning terrain ahead of you. The picture is computed from stored data against your GPS position.
• Currency does not equal completeness. A current database still cannot show unlisted obstacles, new construction below 200 feet AGL, or structures never formally cataloged.
• GPS spoofing is the silent failure mode. Jamming flags a problem; spoofing shows you a convincing picture of the wrong location.
• The terrain picture inherits AHRS errors. An attitude sensor fault will corrupt the synthetic terrain rendering. Backup instruments exist for exactly this reason.
• The instrument scan is non-negotiable. The picture is a supplement to your scan, not a replacement for it. Automation complacency is a documented behavioral pattern - knowing it exists is the first step in guarding against it.