Commercial, Military

Synthetic Vision: No Longer Futuristic

By James W. Ramsey | February 1, 2004

Little more than a decade ago, Gordon Pratt, president of Chelton Flight Systems, was asked why there were no new electronic flight instrument system (EFIS) products and why manufacturers of new-design aircraft had to install 1950s-vintage flight directors and horizontal situation indicators (HSI). In response, his newly formed company began looking into synthetic vision. Once viewed as futuristic, synthetic vision systems (SVS) may appear in military and air transport cockpits within the next three to five years, thanks to breakthroughs in space-based terrain mapping. Lower-cost SVS systems now are flying in general aviation (GA) aircraft, because of work by Chelton and at least two other avionics firms.

Synthetic vision is a three-dimensional "virtual view" of terrain designed to enhance safety in low-visibility conditions. An SVS system's terrain and obstacle database, used in conjunction with GPS precision navigation, provides pilots with a realistic depiction of the environment outside the aircraft, along with flight path guidance. Synthetic vision also can provide surface guidance for taxi and takeoff in low-visibility conditions. And it can interface with warning devices, such as terrain awareness warning systems (TAWS) and traffic alert collision avoidance systems (TCAS), and incorporate data link inputs that provide warnings, notices to airmen (NOTAMs), and even near real-time weather information.

A major step forward in terrain mapping came with the February 2000 launch of the space shuttle Endeavor and it's 11-day shuttle radar topography mission (SRTM). Analysts at the National Imagery and Mapping Agency use the SRTM data to generate the 3D topographic maps of the Earth.

This accelerated the development of a system flying in GA aircraft. Coupled with Jeppesen navigation charts, the system displays a "highway in the sky" that guides pilots through a series of waypoints, standard terminal arrival routes (STARS), and ILS approaches to landing. Terrain, obstructions and traffic (courtesy of automatic dependent surveillance-broadcast, or ADS-B) also can be depicted on the displays.

Three-Way View

To check on the status of this emerging new technology, in large aircraft as well as small GA planes, Avionics Magazine visited Rockwell Collins' advanced technology center (ATC) in Cedar Rapids, Iowa, and also flew in a 300-mph, single-engine Lancair IVP experimental aircraft to view Chelton's synthetic vision EFIS.

Collins has been partnering with NASA's Langley Research Center, the U.S. Air Force Research Lab (AFRL), and Boeing-Jeppesen in developing a terrain database to support its SVS. When the database is combined with the GPS location of the aircraft, the pilot can clearly "see" the flight environment from three different views:

  • From the cockpit (egocentric),

  • Outside-the-aircraft (exocentric), and

  • Coplanar–map and vertical profile.

Collins plans to have dual displays: a primary flight display (PFD) to depict a tactical pathway with underlying terrain and an accompanying multifunction display (MFD) to provide a strategic look at the entire flight plan area. For retrofit on aircraft that may not have a modern EFIS, the company proposes simplified formats suitable for use on a head-up display (HUD).

Collins' SVS was tested last year aboard Boeing's 737-900 technology demonstrator. Airline customers and the Federal Aviation Administration (FAA) participated in the tests and data gathering, which took six months. It was determined that SVS is a promising but "emerging technology" that will require more evaluation and testing.

Designed primarily to enhance situational awareness during takeoff and landing approaches, synthetic vision also can help pilots avoid prohibited or restricted airspace. For example, they can steer clear of the highly secure airspace near Reagan National Airport, in Washington, D.C., as well as handle noise abatement procedures.

"Looking at all these complex procedures that are being developed, pilots need more [information] on the flight deck than what they currently have to make future operations as safe as current operations," says Tim Etherington, Collins' technical director� synthetic vision projects. "Today, we can do a zero-zero Cat III landing with nothing more than knowing that the [ILS] beam is guiding us to a runway and that we've got a controlled airport environment. Eventually, we should get to where the integrity of that SVS, data-based information isn't any different from that used for Cat III landing."

Collins plans to have SVS systems "transition to [its] product centers in the three- to five-year time-frame," Etherington reports. The company will target the business, regional, large air transport and military markets.

Development of Collins' SVS commenced five years ago, when a set of NASA-sponsored workshops evolved into requests for proposal. These were followed by contract awards–in Collins' case for SVS in the "high-end thrust" category of aircraft, ranging from business jets up to air transports. The company is in the third phase of contracts with NASA-Langley under NASA's Aviation Safety program. The third phase was scheduled to culminate in a flight test last summer, but was postponed while NASA conducted an internal safety review following the Columbia space shuttle disaster. The final flight tests have not yet been scheduled.

Colorado Tests

Initial flight testing of Collins' SVS package began at Dallas-Fort Worth in 2000. The following year the testing was transferred to Eagle, Colo., using NASA's B757. Served by American, Delta and United airlines during Colorado's busy ski season, Eagle offered unique challenges in dealing with terrain and weather conditions, and was ideal for the SVS tests.

The approach to Eagle requires crossing an 8,200-foot ridgeline and then descending to the airport. To execute a missed approach on the main runway, the aircraft must have a flight management system (FMS) and the pilot must use an area navigation (RNAV) procedure "that has the aircraft following rising terrain, turning to miss [8,100-foot] Snow Mountain, and then flying up a canyon. So we were climbing with the terrain as it went up," Etherington exclaims.

These terrain features normally result in high-minimums (the minimum height above terrain at which the pilot must have visual contact with the runway), although American had received FAA approval to lower its minimums to 1,400 feet above ground level (AGL). During the Eagle tests, NASA simulated an "engine out" on all departures and took approaches down to 200 feet AGL with SVS.

For approach to another Eagle runway, American was authorized to visually execute a 180-degree circle with the B757 in a valley with a diameter of less than four miles (5.4 km). "We turned this [maneuver] into a synthetic vision guided procedure for the flight tests, so not only did we provide a view of the synthetic terrain, but we also provided guidance for the circle approach to the runway," says Etherington. Pilots participating in the tests were directed by "tunnel guidance," i.e. by maintaining an aircraft symbol's position on the display through a progression of framed imagery. "The tunnel was set up using a computer to compensate for predicted wind effects," he adds.

Pilots from United, American, Delta, FAA and Boeing flew some 80 approaches at Eagle, using both NASA and Collins SVS concepts. The evaluation pilots' view was blocked, simulating instrument conditions. In all the approaches, "not once was the airplane not in a position to land," Etherington claims. The NASA concept, broadly speaking, is to use detailed terrain depictions, Etherington says. NASA, for example, " uses a very photo-realistic picture splashed onto the HUD."

In the Colorado tests Collins also demonstrated its SVS for surface guidance in low-visibility conditions. With the exocentric view, this time on the PFD, the system showed wing tip clearance and widths of runways and taxiways.

Air Force Tests

Rockwell Collins also has been working with the U.S. Air Force to demonstrate low-level military approaches using synthetic vision. Flights in November 2002 at Edwards AFB, Calif., were the culmination of a two-year cooperative research agreement between Collins and AFRL.

More than 20 hours of flight tests were performed on the USAF's C-135 Speckled Trout aircraft. Low-level terrain sorties were flown in simulated night, instrument meteorological conditions (IMC). The tests were the first to use synthetic vision displays for a zero/zero approach to landing at an assault (non-surfaced) strip, Collins maintains. The company is working on its second Air Force contract to provide "pathway guidance" for military applications, specifically for C-130 low-level missions.

Air Force test pilots at Edwards flew "blind" low-level profiles and approaches using Collins' HUD and head-down displays equipped with synthetic vision elements. Flights began at the Mojave Test Range, near a mountainous region with steeply rising terrain.

"The pilots couldn't see anything outside. They were flying the aircraft at 600 feet off the ground, centering on the middle of the [synthetic vision] tunnel, flying this terrain-following mission profile," says Etherington. "At Mojave, the pilots conducted a circle to land, still not looking outside the cockpit."

Test pilots also used synthetic vision to conduct a military overhead approach at Edwards. They initiated their approach at 12,500 feet, then conducted two 360-degree turns with an 8- to 10-degree descent, and finally flew a short final approach in position to land on the runway.

Special cockpit instrumentation for the NASA and military tests was kept to a minimum. Extensive hardware modifications to the flight deck were avoided. The NASA B757 included an 18-inch liquid crystal display (LCD) mounted in front of the aircraft's standard instrumentation. A Collins/Flight Dynamics HGS 4000 HUD also was installed in the aircraft. The military tests used a standard LCD display, as well.

Winning Combination?

SVS contrasts with enhanced vision systems (EVS), which use aircraft-mounted sensors (currently infrared) to "see through" clouds or fog and show features in darkness. Recognizing that even SVS has limitations–for example, the terrain database would not show a large animal wandering on to the runway–Collins envisions an SVS-EVS combination in the future, once such a system becomes affordable.

Collins is working with AFRL under a synthetic-enhanced (SE-Vision) program, looking at integrating the technologies on a PFD and "doing some things on the MFD, as well," Etherington says. NASA is a government-funded partner with AFRL.

A forward-looking infrared camera is a "natural combination" on a PFD, Etherington asserts. But even a PFD display typically has a wider field of view than the sensor. One way of getting around this variation is to put the sensor field of view in the middle of the display view and fill in the rest of display view with synthetic vision imagery.

There's room for both SVS and EVS separately, Etherington says. But the military, because of its more demanding requirements, may want the combined systems, if they can afford them. Collins wants to look at bizjet, regional and air transport applications for SE-Vision on the commercial side and transport and special forces missions on the military side.

It's also possible that adding EVS "could help the integrity–trustability–of the whole system," Etherington says. "The sensor is aircraft-referenced, and the pilot has more faith and trust in an airframe-referenced system." But cost/complexity eventually will determine whether an "SE" solution, SVS-only, or EVS-only will proceed.

Chelton Flight Systems

While the air transport and military markets evaluate synthetic vision, general aviation is adopting, installing and operating it. Chelton gained FAA approval for its EFIS synthetic vision system on a PFD in 2003–the first company to reach this point. The certification enables operation in up to 600 (Part 23) aircraft types, ranging from Piper Cub to Cessna Citation and (since July 2003) including helicopters. Pratt estimates some 24 certified systems have been installed and are flying. FAA gave Chelton its biggest boost, selecting the EFIS/SVS for the agency's Capstone Phase II program in Alaska. FAA is "equipping every commercial aircraft in southeast Alaska with one of our systems," says Pratt. "This could be as many as 200 aircraft."

The company's SVS involvement began with Sierra Flight Systems, a startup launched in the mid-1990s, which was acquired and renamed by Chelton Group in 2001. In 1996 Sierra flew a proof-of-concept EFIS, which a year later featured synthetic vision imagery called "highway in the sky." By 1999, Sierra was delivering its new EFIS 1000 and 2000 products to the experimental aircraft market.

Moving beyond the experimental market, Chelton Flight Systems repackaged the system, calling it the FlightLogic synthetic vision EFIS (Dec. 2003). This incorporates "proprietary compression routines that can put an entire continent of terrain on the system at once," says Pratt.

The company plans to reach beyond general aviation to corporate jets, especially ones with mechanical flight directors and horizontal situation indicators. "We can give them about a 250-pound [113-kg] increase in useful load just by getting rid of that old [mechanical] equipment," says Pratt. Chelton's FlightLogic also is compatible with a version of� TCAS and will show targets on the PFD.

Chelton's EFIS/SVS system consists of three software pages–PFD, moving map, and engine monitor–shown on sunlight-readable, high-resolution color LCDs. The� MFD projects a moving map, using Jeppesen's airport and navigation data. The map shows the flight path, along with terrain and obstacles, and is integrated with a voice warning system for aural alerts. The U.S. Department of Defense provides the terrain data–the same used for TAWS. FAA provides the data on obstacles and towers. FlightLogic's SVS uses the PFD to present highway-in-the-sky navigation for waypoints and approaches. A velocity vector projects the aircraft's flight path, allowing the pilot to guide the aircraft through a 3D series of "boxes" (the tunnel) on the screen.

Universal Avionics

Universal Avionics Systems Corp. can claim the first certified SVS, having received technical standard order (TSO) approval in June 2002. But its Vision-1 system was approved for an MFD only and is not approved for a PFD. FAA certified only Vision-1's exocentric view, making it a situational awareness tool but not a navigational aid.

Universal plans to gain certification of an egocentric view on a PFD soon. (It is installed already in the company's King Air 350 test bed aircraft.) However, it will provide the highway-in-the-sky feature only in the exocentric view. Universal believes the concentric windows that produce the egocentric highway in the sky can become confusing to the pilot. Vision-1, therefore, will remain a situational awareness tool and not a navigation aid that provides guidance cues on the PFD.

The Tucson-based company has followed a phased approach to SVS development, progressing from an exocentric view to an egocentric view. In SVS certification, the company is seeking approval for its egocentric view on PFDs, first in Part 23 aircraft and then in Part 25 aircraft.

"We're targeting the Part 25 market, so our system has to go through greater scrutiny than with Part 23," says Dan Reida, Universal's manager, airline programs. This scrutiny has prompted FAA to form a multiple-expert opinion team (MEOT), a group of experts tapped when the agency has few guidelines to approve a new technology. "The MEOT has made comments [regarding Vision-1's egocentric view], and we're addressing them," he adds. �

Specifically, according to Grady Dees, Universal's director of engineering services, one comment involves how the synthetic image conforms to the pitch scale. "Our display is conformal," says Reida. "But the MEOT wants to ‘enhance' the image to make the terrain appear a bit more threatening," Dees adds. Another comment involves a "software tweak" to compensate for air data system anomalies under certain conditions, usually during takeoff.

Universal hopes to have the Vision-1 egocentric view approved early in 2004. And by May they plan to have the new EFI-890R (R for replacement) display certified and available as either a nav display or PFD. The company then intends to have both the egocentric and exocentric views of Vision-1 available for presentation on both its new 8.9-inch diagonal EFI-890R display and its 6.4-inch MFD-640 display, already fielded. Universal has sold Vision-1 to business aircraft customers and has "strong interest from a military customer" says Reida.

SVS from AGATE

Avidyne has pursued SVS research through a three-year contract under NASA's Advanced General Aviation Transport Experiments (AGATE) program. The company's FlightMax/Entegra integrated flight deck system for small aircraft boasts an extended horizon and all standard flight instrumentation on the PFD and moving map/terrain/obstacle data on the MFD. Both are 10.4-inch, high-res displays.

HUD vs. Highway in the Sky

A synthetic vision system (SVS) has advantages over a head-up display (HUD), not the least of which is expense. "The advantage, aside from tactical military aviation, is that we show [on SVS] everything that is out there–aircraft, terrain, towers, antennas obstructions, navaids and airports up to 40 miles away," says Chelton Flight System's Gordon Pratt, referring to his company's FlightLogic EFIS/SVS. Chelton's system uses HUD-type symbology on a primary flight display (PFD), with heading across the top, airspeed and altitude down the sides, leaving the center open to display synthetic vision and "highway in the sky" symbology.

In a HUD, the center is left open to see out ahead of the aircraft, which in instrument flight rules (IFR) conditions, "does not do you any more good than looking at an instrument panel," Pratt exclaims. Since the SVS shows the runway environment in correct scale and perspective, transition from head-down to head-up, out-the-window viewing for landing is very rapid, because when the pilot glances up, the runway will be precisely where it is shown on the screen, he explains. The system guides a pilot from departure to destination airport, Pratt says.

"It takes you through all the en route procedures, the approach and right down to the missed approach point," he adds. The missed approach procedure is shown on the PFD as a tunnel (concentric windows), and SVS calculates the correct entry to the holding pattern based on the aircraft's flight path. The pilot has two options: either fly the aircraft through the tunnel manually, centering the aircraft symbol presented on the display, or engage the autopilot and let it automatically fly through the tunnel.

FlightLogic is very fault- tolerant. "If you lose GPS, you still have navigation because of the accelerometers in AHRS [attitude heading reference system]. If you lose AHRS, you have a GPS moving map. If you lose air data, you still have position information and altitude from GPS. And if you lose one display, the other takes over," says Brent Regan, Chelton's chief hardware engineer.

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