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X-Ray Vision and Alphabet Soup - Decoding GA Vision Systems

Source: www.faa.gov/news/safety_briefing, By James Williams

I may be part of the last generations to remember the ads for X-ray glasses that appeared in the back of comic books and magazines aimed at young people. These mail-order novelties usually sold for a few quarters, or dollars in the later years. Of course they weren’t exactly legit, but who wouldn’t be willing to risk a few bucks for even the slightest chance for such power? Well, as it turns out, the power of “X-ray” vision is not so much of a far-fetched novelty anymore — at least in aviation.

decoding GA vision

We now have two technologies that allow us to literally see through the dark and the clouds. While there is some overlap in this technology, this article will focus on Enhanced Vision (EV) and Synthetic Vision (SV), rather than night vision. For more information on night vision, please see the articles listed in the Learn More section. EV and SV use very different approaches and technologies to give you a bright and clear picture of the outside world, no matter how dark or cloudy the sky may be. Naturally, each of these approaches has its advantages and drawbacks.

Synthetic Vision

SV is by far the more accessible in terms of cost and equipment. It relies on marrying technologies already included in many avionics suites and even some hand-held systems. SV uses a detailed and high quality database of terrain features and obstacle data to create a virtual ‘world.’ The SV system uses an accurate aircraft position provided by an on-board GPS to display this virtual world around your aircraft. The advantage of this system is that regardless of the weather or light conditions, you will have a “clear view” out of the front of the aircraft. You could literally paper the windshield of the aircraft (not a suggestion, mind you!) and still see outside. It’s important to remember that SV is not a navigational system. SV designed to improve situational and terrain awareness and is not intended, or authorized, to be used as a navigational system.

There are two potential faults though — location data and database information. While GPS is usually very reliable, its weak signal is vulnerable to interference. Although, the FCC has done a great job of shielding GPS frequencies, the possibility exists that someone transmitting on or near those frequencies could potentially jam the GPS. And of course there’s the potential for active interference or spoofing, but that’s usually limited to military action. These GPS issues are not a fault with SV and apply to any
system that uses GPS.

The other potential issue is the quality and currency of the database used to create the virtual world your aircraft is relying on for safe navigation. While terrain is pretty much static, obstacles are constantly changing. This is probably the biggest issue with SV, because what you’re seeing may not be a 100 percent accurate depiction of the actual
world outside. In other words, your SV system is only as good as the its foundational database. So it is worth investigating how adept a system is at creating and updating that database.

But perhaps the best advantage SV has is its relatively low cost. You can add it to many popular flight instrument systems or even utilize systems built into accessories like a portable GPS unit, or an app on your tablet. There are many variables, so it’s worth investigating which one best suits your needs.

Enhanced Vision

EV may seem like a close cousin of Synthetic Vision, but it’s actually a very different technology. EV uses sensors on the aircraft to “see through” weather or darkness. While this sensor comes in a variety of forms, by far the most common is infrared (IR), which senses temperature differences and produces a high quality real-time image of the outside scene. EV allows a pilot to see through darkness, smoke, haze, smog, dust, light fog, and even rain. In heavier conditions, EV may lose some of its ability relative to SV, but what it shows you is what’s actually out there, not what the database says should be out there.

There are a wide variety of EV systems on the market and prices vary greatly, for good reason. The older and more advanced systems use a super cooled IR sensor to allow the sensor to more easily detect the temperature differences. However, these systems require a mechanical means of cooling, which limits the number of aircraft that can support this added equipment and which can add significantly to the installation cost. Previously, EV was the purview of high-end business jets as an installation could run close to a million dollars. Even on the cheaper end it probably was between $250,000 and $500,000. More recently, new systems have come onto the market that don’t require mechanical cooling. With this new generation, we’re looking at a ballpark figure of $25,000. While still a significant investment, this price point brings EV to the realm of possibility for GA.

The key advantage of EV is that what you see is what’s actually outside. There’s no concern about the location inaccuracies or the database being out of date. That being said, the very significant cost difference, many thousands of dollars vs. a few hundred, means that EV isn’t nearly as accessible as SV.

What Difference Does One Little Letter Make?

Some eagle-eyed readers may have noticed I’m using EV in lieu of Enhanced Flight Vision Systems (EFVS) or Enhanced Vision Systems (EVS). You may have also noticed I didn’t mention anything about the operational credit that is given to EFVS on approaches. This was intentional. While it may seem like the only difference is one little letter, it’s not — at least as far as FAA regulations are concerned. First and foremost, the regulations permit a qualified EFVS to be used in lieu of natural vision to descend below DA/DH or MDA down to an altitude of 100 feet above the touchdown zone elevation provided all of the requirements of 91.175(l) are met. Those requirements include enhanced flight visibility, visual reference, and other operating requirements.

Second, to qualify as an EFVS, the sensor image must be displayed on a Head Up Display (HUD) along with the other required flight information and flight symbology specified in 91.175(m). The EFVS imagery and other cues which are referenced to the imagery and external scene topography, must be presented so they are aligned with and scaled to the external view. EVS does not meet these requirements. This becomes a big issue for fitting an EFVS in most small GA aircraft. So while the information presented on an EVS might be very similar to that of an EFVS, the lack of a HUD will prevent the EVS from using the operational credit that an EFVS would receive.

synthetic vision on iPad

Like Peanut Butter and Jelly

Some things just go together. While we’ve largely compared these two systems independently, there is a compelling argument for combining them. Although you could operate these independent systems side by side, a more powerful solution is what’s called a Combined Vision System. “A CVS is based on a combination of different technologies that may include both real-time and computer-generated images,” Terry King, an Engineering Psychologist and FAA expert explains. “While no CVSs are currently approved for operational credit, the regulations make provision for the FAA to approve ‘for credit’ operations for future CVSs that might be certified and operationally approved for these operations.” King adds, “Depending on the operation, this may require an operator to obtain authorization to conduct these operations.”

Each system has its limitations and advantages. Used independently or in combination, these systems will improve situational awareness and safety. If your budget can justify it, Synthetic Vision and Enhanced Vision can give you those X-ray glasses you always wanted, but didn’t get as a kid.

Learn More

“Brushing Back the Dark,” FAA Safety Briefing, Jan/Feb 2014, p. 20: http://go.usa.gov/csEYj

“T=Terrain Avoidance” FAA Safety Briefing, Nov/Dec 2015, p. 28: http://go.usa.gov/csEg4

James Williams is FAA Safety Briefing’s associate editor and photo editor. He is also a pilot and ground instructor.