The possibility of business jets and airliners making autonomous low-visibility approaches and landings to airports without an ILS has moved closer to reality with the success of a six-month test of a flight guidance and display system featuring integration of both synthetic and enhanced vision techniques.
In a series of test and demonstration flights concluded last month, government and industry engineers and pilots performed multiple virtual visual approaches independent of ground-based navaids. A hybrid system of synthetic and enhanced (infrared sensor) vision dubbed SE-Vision has shown its ability to integrate database-derived symbology and real-time thermal imagery of the surface during a series of developmental, evaluation and demonstration flights from Atlantic City, N.J., and Albuquerque, N.M.
The program was conducted by a coalition of DOD and civilian government entities along with systems suppliers Rockwell Collins and Max-Viz. Initial demonstration flights began in January with precision approaches in VMC to Atlantic City International Airport, where the last of the dual-purpose military/civil evaluation missions was flown late last month.
Low, Fast and Bumpy
A June 7 demonstration aboard an FAA Technical Center Boeing 727-100 took off from Albuquerque’s Sunport International Airport along a ground-hugging route northward through steep canyons and narrow valleys of the southern Rocky Mountains. The flight profile consisted of a simulated military precision stores-drop mission along a digital database-defined route, flying as low as 500 feet agl at 250 kias in moderate turbulence, followed by a self-controlled approach to 60 feet agl at the Alamosa, Colo., airport.
During the approach, the pilot used only a head-up display (HUD) for guidance. In addition to standard HUD symbology, projected onto the combiner glass was a synthetic-vision picture of surrounding terrain with an inset window presenting a real-time thermal imagery view of the approach and runway environment.
The synthetic vision computer generated “tunnel in the sky” steering cues that the pilot used to follow a curved approach path.
Collins engineer Tim Etheridge said the SE-Vision database can construct a full circling self-contained approach with vertical guidance “anywhere in the world, down to 100 feet.” The real-time enhanced vision component introduces a factor of trust in the synthetic vision database that will encourage pilots to feel comfortable in relying upon it, he predicted. Etheridge concluded that the system “lowers pilot workload and increases situational awareness.”
Business Aviation Applications
Thermal imagery-enhanced synthetic vision will almost certainly become operational first with the military, which does not confront the documentation and verification hurdles that face civil aircraft operations. Still, evidence of the FAA’s growing interest in synthetic vision-based solutions for autonomous in-flight guidance, terrain avoidance and precision instrument approaches is the agency’s collaboration with the U.S. Air Force Research Laboratories at Wright-Patterson AFB to conduct the SE-Vision flight-test program.
While neither Collins nor Max-Viz would predict when and with whom an SE-Vision-like system might emerge in the business aviation market, Gulfstream currently appears the most interested in applying synthetic vision concepts to its products, at least its top-of-the-line models.
A Gulfstream representative was an observer aboard the June 7 flight. In a program leading to this year’s flights, last summer NASA and Gulfstream test pilots flew a GV equipped with a Collins synthetic vision system to develop and evaluate means of monitoring database integrity. Potential civil applications for an SE-Vision display system would include firefighting and EMS as well as corporate transport, air-taxi and charter work.
Both Honeywell and Universal Avionics have developed and continue to refine synthetic vision concepts, software and display equipment, but neither is known to have conducted as lengthy and thorough a flight demonstration and evaluation program as the Rockwell Collins/Max-Viz team.
The SE-Vision hardware suite includes a Rockwell Collins Flight Dynamics HGS 4000 HUD display and computer, a prototype head-down LCD combination primary flight and navigation display and a Max-Viz dual IR sensor enhanced vision system (EVS) with image fusion processor. The Collins synthetic vision symbology generator processes a virtual picture of the ground environment constructed from a publicly available NASA terrain database.
The SE-Vision database is revised to reflect current notams, airspace restrictions and other pertinent changes. It is possible to do a real-time database update in flight using a broadband wireless datalink.
A modified Collins WXR-2100 multi-scan weather radar verifies database surface feature heights, detects obstacles and monitors the runway. Although its main function is to verify the accuracy and currency of the synthetic vision database, the EVS also detects and displays moving objects in the air and on the ground.
During a landing approach, when the synthetic and real-time thermal images of the runway merge, the SE-Vision computers generate a “virtual ILS” signal for precise guidance on final. In the SE-Vision system aboard the 727 testbed, pilots could manually vary the ratio of synthetic vision to real-time enhanced vision on the combined display. Production systems are expected to feature software that controls that mix.
The Max-Viz EVS-2500 thermal imaging system in the SE-Vision suite consists of two forward-looking uncooled IR sensors linked to an image fusion processor. The infrared cameras operate in two distinct sectors of the IR spectrum–short-wave and long-wave.
The short-wave camera, closer to the wavelength of visible light, is more receptive to LED and strobe lights, which emit very little thermal energy. It provides optimized display of runway, taxiway and aircraft position lights. The long-wave camera has superior penetration of haze, dust, smoke, mist and light rain, as well as greater resolution of objects with small thermal differences.
Dr. Richard Kerr, Max-Viz research director, said the uncooled sensor offers great reliability in a small, light package. He added that unlike larger, higher-priced cryogenically cooled IR sensors, the Max-Viz uncooled units’ sensitivity “surpasses the cryo-cooled cameras in this application” and have “instant ‘on’” capability that externally cooled IR cameras do not.
This year’s series of FAA/USAF flight tests has verified the SE-Vision system’s ability to precisely display aircraft position relative to specific points on the ground. The system also computes exact height above the ground derived from a blend of radio altimetry and GPS data.
To achieve an accurate update for the barometric altimeter in remote locations where altimeter setting broadcasts are unavailable or irrelevant, the SE-Vision-equipped aircraft use synthetic vision guidance to overfly a waypoint with a precisely defined msl altitude. Adding the radar altimeter height above the waypoint provides an altitude to which the baro instrument can be set.
Rockwell Collins electrical engineer Richard Jinkins said millimeter wave (MMW) radar or high-resolution commercial airborne weather radar will join the sensor mix for improved penetration of certain obscurants near the surface to maximize precision approach capability and prevent runway incursions. Max-Viz has teamed with Sierra Nevada to develop a 94-GHz MMW with the aim of integrating it with a dual-sensor thermal imaging EVS for true all-weather approach capabilities down to Category III minimums.
SE-Vision will operate independently of an EGPWS. In fact, there is no EGPWS installed in the FAA Boeing 727 testbed.