Better than a magic button

In October 2000, as the world was still welcoming the twenty-first century, Gulfstream Aerospace announced its enhanced vision system (EVS), a device that would prove more valuable than any magic button. EVS offered Gulfstream operators improved operational capabilities, like the ability to land in Categories II or III weather at thousands of airports only equipped with Category I precision approach systems. The EVS enables pilots to spot the landing runway in daylight or at night in reduced visibility conditions much better than was possible with the human eye.

The first EVS captured an image of the landing runway, terrain, or obstacles ahead using a Kollsman forward-looking infrared (FLIR) camera installed in the nose of the aircraft. The camera can see through most obscurants (e.g., fog, smoke, smog) and display the image on the pilot’s head-up display (HUD). Depending upon the visibility obscuration characteristics and the strength of infrared energy emitted from the approach lights or reflected from the runway environment, the pilot can identify visual references by looking at the image on the HUD. The EVS image displayed on the HUD is monochromatic and two-dimensional but is an easily interpreted real-world rendering.

The system adds just 50 pounds to an aircraft’s empty weight. So unique was the EVS that the FAA determined special certification conditions should be issued to establish an equivalent level of safety for the use of enhanced vision because at the time regulations only addressed natural vision without considering the concept of electronic or enhanced vision.

Gulfstream crews flew more than 100 system development test flights early on. The company and the FAA then conducted an extensive proof of concept flight demonstration program concluding that the EVS could be certified to provide an image that would assist the pilot during an instrument approach in detecting and identifying the visual references listed in FAR 91.175(c)(3) for descent below decision height to 100 feet above the touchdown zone. Those references include the runway threshold or threshold markings, the threshold lights, the runway end identifier lights, the touchdown zone lights, or the runway lights.

The FAA revised the operating regulations to specifically address an enhanced flight vision system (EFVS), which is an installed EVS certified to provide operational credit, initially creating subparagraphs 91.175(l)(m). Subsequently, EFVS was removed from 91.175, and 91.176 was created to address straight-in landing procedures using an EFVS specifically. EVS was certified on the GV in 2001 and later became standard equipment on the company’s new aircraft models.

“The whole purpose [of an EFVS]  is to extend the visual segment by using enhanced vision instead of natural vision to see further through the fog.” –Gary Freeman, retired lead EVS test pilot, GulfstreamSome pilots initially believed, incorrectly, that an EFVS would automatically earn them reduced landing minimums. Gary Freeman, Gulfstream’s recently retired lead EVS test pilot, clarified the discussion about minimums. When an EFVS is in use, the published minimums “are exactly the same. The whole purpose is to extend the visual segment by using enhanced vision instead of natural vision to see further through the fog.” This allows pilots to land in Category II or III weather.

When a pilot spots the runway lights looking through the EVS, the call is “EVS lights in sight.” If those lights are in sight in the image on the HUD before descending through the published DA, the pilot can continue the approach to 100 feet under 91.176(b). If the pilot can see the required visual references without relying on EFVS before 100 feet above the touchdown zone elevation, the crew can continue the landing. If, however, the crew sees only the lights in the EVS image at 100 feet, a go-around is required. At 100 feet, the required items must be seen with natural vision.

There are a few idiosyncrasies to an EVS. Enhanced Vision is real-time, much like the backup camera in a car. The image must be real-time to gain any advantage for landing. For instance, scene contrast detected by infrared sensors can be much different than that detected by natural pilot vision. On a dark night, thermal differences of objects, not detectable by the naked eye, will be easily detected by many imaging infrared systems. On the other hand, contrasting colors in visual wavelengths may be distinguished by the naked eye but not by an imaging infrared system. Where thermal contrast in the scene is sufficiently detectable, the pilot can recognize shapes and patterns of specific visual references in the infrared image. However, depending on conditions, they can also appear significantly different to a pilot in the infrared image than they would with normal vision.

While an EVS will detect the energy emitted from traditional incandescent runway lights, it will not detect the light frequency emitted from the new LED lights that some airports are replacing their runway lights with. “The runway lights, which are what the EVS was really designed to detect, put out a lot of energy in the visible spectrum at the 0.6 to 0.8 microns wavelength,” Freeman said. “Most of the energy from incandescent lights is not in the visible spectrum and is around the 1.2-micron area, which is not visible to the human eye but is very visible to our infrared camera. All of the energy that LED lights emit when installed at airports is not in the infrared spectrum and, hence, is not visible to our camera. However, the runway and landing environment can be seen with the EFVS regardless of the installed lighting.”

Gulfstream’s innovative EVS was so successful that when it was installed in a G550, the company won the coveted Collier Trophy in 2003. Over the past two decades, most other business aircraft builders followed suit with similar technologies. In 2004, Cessna Aircraft, a subsidiary of Textron Aviation, began offering EVS as an option on large-cabin Citation X and later on the Citation Excel and XLS. French aircraft builder Dassault chose a slightly different path, combining their EVS with computer-generated synthetic vision to create the FalconEye system for its Falcon jets. And now, Gulfstream’s Combined Vision System unites an enhanced flight vision system and synthetic vision system on dual head-up displays.

Rob Mark is a journalist, business jet pilot, and flight instructor. He publishes the industry blog Jetwhine.com