Visual Flight Rules (VFR) define a minimum of clear weather conditions under which a pilot can operate an aircraft using visual cues, such as the horizon and buildings. Under VFR, a pilot is expected to “see and avoid” obstacles and aircraft, and essentially only needs to see out of the window.
When hazardous weather conditions exist, Instrument Flight Rules (IFR) allow an aircraft to primarily operate by referencing instruments; flight by outside visual reference is deemed unsafe. To fly using instruments, the pilot needs, at a minimum, an attitude indicator or heading source, an altimeter, and airspeed.
In a sense, a Synthetic Vision System (SVS) brings VFR directly into the flight deck, providing situational awareness when weather conditions obscure visual ability to fly safely. The SVS, a computer-generated view of the outside terrain, is based on precise Global Positioning System (GPS) location, aircraft attitude, and an advanced worldwide terrain and obstacle database. The onboard terrain databases create a computer-generated 3D perspective of the topography outside of the aircraft. Obstacle databases can be used in conjunction with terrain databases to enhance situational awareness by providing depiction of man-made obstacles like structures and tall buildings. From approach to landing, SVS technology gives pilots the ability to see through the night, snow, fog, and other conditions.
The pilot’s view, however, has improved, opening up new possibilities for flight.
Developed by NASA and the U.S. Air Force in the 1970s and 1980s, SVS technology has since migrated into the civilian aviation community. Universal Avionics Systems Corporation, for example, certified its Vision-1® SVS product with the Federal Aviation Administration (FAA) in 2005. The company has also made its technology available to operators of business aircraft and larger planes.
The Vision-1 “Egocentric” pilot’s view (see Figure 1) is designed for Primary Flight Display (PFD) and Electronic Attitude Director Indicator (EADI) applications. The display provides the pilot with a perspective as if he or she is looking out of the flight deck window. The system maintains the standard foreground symbology and replaces the blue/brown background with imagery depicting the terrain in real-time, complete with pitch and roll — important flight dynamics parameters.
The “Exocentric” wingman’s view (see Figure 2) provides a 3D look of the aircraft, with respect to the flight path and surrounding terrain. The perspective appears as if from a camera situated behind, above, and to the right of the aircraft.
Universal Avionics also added a Synthetic Vision System to its new InSightTM Integrated Flight Deck. Shown at the National Business Aviation Association (NBAA) 2014 Convention and Exhibition, the technology’s graphics depict terrain, ice and water features, advanced airport maps (ramp areas, terminal buildings, taxiways, and hold lines), special-use airspace, and urban area outlines.
Today’s SVS features realistic portrayal of ice-capped mountains and deep blue seas. An algorithm considers the reflectivity of the water, rather than just drawing blue water for lakes, rivers, and oceans. Now reflections and shimmering waters give operators indications to their location. Advanced shadowing, water and snow features, and a 3-arc-second resolution create a sharper image than traditional SVS flight decks. Compared to aircraft that are not equipped with SVS, the difference is like driving at night in the fog versus driving on a clear day. The technology helps a pilot easily understand his or her environment.
Because the vision system is integrated into the aircraft onboard avionics system, pilots can configure the layout of the flight deck instruments according to personal preference to allow for enhanced situational awareness. Additional embedded critical functionality includes electronic charts, radio control, and broadcast weather. The integrated SVS technology interfaces with a large number of federated components, such as attitude/heading sensors, air data computers, radars, traffic systems, radios, and autopilots.
Benefits and Possibilities
The benefits of SVS are evident for pilots; it provides the pilot with a dynamic perception of position, trend, and motion. In addition, the vision system lowers mental workloads, enhances visualization in low-visibility conditions, reduces flight technical error, and improves the ability to detect and avoid Controlled Flight Into Terrain (CFIT) situations, where a piloted aircraft is inadvertently flown into the ground, mountain, water, or other obstacle.
In the future, other SVS possibilities exist, such as lower landing minimums. A pilot’s landing minimum determines an appropriate altitude for an aircraft’s approach, based on factors such as weather and visibility.
Established in 2006, RTCA Special Committee 213 (SC-213), an international collaborative effort of government and industry, creates consensus requirements for SVS and Enhanced Flight Vision Systems (EFVS). The group is currently developing Minimum Aviation System Performance Standards (MASPS)-level guidance for SVS, Enhanced Vision Systems (EVS), Combined Vision Systems, and EFVS. RTCA SC-213 Synthetic Vision Guidance System (SVGS) MASPS is expected to be released in upcoming months, and will capture SVGS operational credit requirements for a lower minimum of 150 feet height above touchdown. The system will be used during published Instrument Approach Procedures (IAP) with operational minima that are less than the minima for current Category-I landings. Lower minimums could increase landings under a range of weather conditions.
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