Synthetic Vision Systems

The tail section of Korean Airlines flight 801 stands graphically visible at the crash site in the early morning hours of Aug. 6 1997.

Crash site of Korean Airlines flight 801

On August 6, 1997, Korean Air flight 801, a Boeing 747, crashed at Nimitz Hill, Guam, with 237 passengers on board. The airplane had been cleared to land at Guam International Airport and crashed into high terrain about 3 miles southwest of the airport. 228 people were killed, and the airplane was destroyed by impact forces. Post-crash analysis revealed no mechanical defects with the aircraft (NTSB, 1997).

The National Transportation Safety Board calls this type of accident Controlled Flight Into Terrain (CFIT), in which a functioning airplane is essentially flown into the ground due simply to the pilots’ lack of a clear picture of where they are (Arthur, 2003). According to a study from the Flight Safety Foundation, nearly 80 percent of all fatal airline accidents can be attributed to CFIT or approach-and-landing accidents (North, 1999). Clearly something needs to be done to address this situation and reduce these preventable pilot-error accidents.

During times of reduced visibility, pilots rely solely on the instrumentation in the cockpit and reports from Air Traffic Control (ATC) to maintain a mental picture of their position in space relative to terrain, airports, navigational aids and other air traffic. This “picture” is known as Situational Awareness (SA). Historically, airline and corporate cockpits provided situational awareness through a jungle of dials and gauges, each with its own purpose, communicating such information as bearing and distance from navigational aids (NAVAIDS), aircraft attitude, altitude, airspeed, heading, and various system-health data.

However, with the advent of TV-like screens to display data, called Electronic Flight Instrumentation Systems (EFIS), in military and later commercial cockpits, this instrument jungle was considerably reduced. One CRT or LCD screen was adequate to present the aircraft’s airspeed, attitude, altitude and heading to the pilot. This reduced the number of places to which a pilot’s eye had to travel around the instrument panel when “scanning” the gauges during low-visibility flight. The subsequent decrease in pilot workload meant an increase in situational awareness.

But it was not enough. The problem was this: the early EFIS systems simply replicated the presentation of the old electro-mechanical dials and gauges on a TV-like screen. Little attempt was made to utilize this technology to bring a more user-friendly and intuitive presentation to the cockpit (Nordwall, 2003). Pilots still had to read numbers and chase needles, then mentally create the situational-awareness “picture.”

An emerging concept called Synthetic Vision is a revolutionary attempt to rectify this problem, using EFIS technology to bring maximum situational awareness to the cockpit in the hopes of reducing pilot-error accidents, especially CFIT.

The Synthetic Vision System

Simply put, the idea behind the Synthetic Vision System (SVS) is to use currently-available liquid-crystal (LCD) display technology, Global Positioning System (GPS) receivers and an onboard digital database of terrain, obstacles and airports to provide pilots with a computer-generated, three-dimensional view of the outside world during reduced-visibility flight (Stark, 2001). The primary focus of current research is to provide technology that will not only inhabit the instrument panels of futuristic air transports, but will also be available for retrofit into existing aircraft, including airliners, corporate jets, helicopters and even general aviation light planes.

The Synthetic Vision Systems Project was begun under NASA’s Aviation Safety Program whose stated goal is “to develop and demonstrate technologies that contribute to a reduction in the aviation fatal accident rate by a factor of 5 by year 2007.” The program is a partnership that includes NASA, the Federal Aviation Administration (FAA), members the aviation industry and the Department of Defense.


The purpose of the SVS Project is to design and test a variety of intuitive displays that provide pilots with a perspective view of terrain, obstacles and even real-time traffic and weather information that is “congruent with the pilot’s natural mode of spatial information gathering” (Stark, 2001). Essentially, this means that the more accurately a display can simulate flight under daylight, high-visibility conditions, the better a pilot’s situational awareness.

In addition to experimenting with different views of terrain, coloring, shading, texturing and display size, NASA’s SVS Project is also evaluating several types of course guidance symbology. Current EFIS systems use a variation of the classic “flight director” symbology, in which a crosshairs or miniature aircraft is presented on the attitude indicator (or “artificial horizon”) and guides the pilot to the proper pitch and bank attitudes in order to track the desired course.

However, the 3-D view of the terrain provided by the SVS allows for a novel type of course guidance that shows both current position and the future path of the aircraft. Such systems are called “Tunnel Guidance” or “Highway In The Sky” (HITS). These can appear as a series of boxes strung out in space through which a pilot must fly in order to stay on course.

HITS symbology “allows the pilot to assess the future trajectory relative to the environment at a glance, thus increasing the likelihood of detection of conflicts between the programmed path and the terrain,” as well as allowing smoother and less-tiring aircraft control since the pilot can more easily anticipate future control movements (Theunissen, 2000). In addition, HITS symbology allows a more accurate flight path over all phases of flight including departure, enroute and approach, compared to traditional tracking of the Course Deviation Indicator (CDI) needles found in current cockpits (Chelton). [See image, above right.]

And Synthetic Vision Systems aren’t just prototypes that are gestating in government simulators and university research programs. Actual flight-ready hardware is getting some real-world tests in one of the toughest and historically most dangerous flight environments in the world: Alaska.

The Capstone Program

Due to the rugged terrain, limited navaid and ATC coverage, and unpredictable weather, the state of Alaska was chosen to initiate tests of new technology that will improve aviation safety and efficiency, and eventually provide the techniques essential to the modernization of the entire National Airspace System. The Capstone Program is a joint industry and FAA Alaskan Region effort to provide a working environment for day-to-day operations of these new systems.

Begun in 1999, Phase I of the Capstone Program provided commercial operators in the Yukon-Kuskokwim delta region with GPS navigation receivers, multi-function color LCD displays, and transceivers that helped aircraft see each other during flights in reduced visibility, all free of charge with participation in the program. This equipment provided pilots with access to non-radar (i.e. no ATC) environments that had previously been limited to visual flight operations, and increased the number of airports served by instrument approaches. Pilots’ situational awareness was increased dramatically, simply by bringing information into the cockpit which included terrain, weather, traffic and accurate aircraft position.

Phase II of Capstone began in 2002, moving to the more “environmentally challenged” Southeast Alaska, which is plagued with bad weather, low visibility and rugged terrain. Phase II heralded the first commercial flight of an aircraft equipped with an SVS on March 31, 2003, using a twin-engine Piper Seneca and a Chelton FlightLogic� Electronic Flight Information System with Synthetic Vision (EFIS-SV).

The Chelton FlightLogic system consisted of two separate LCD displays. The Primary Flight Display (PFD) featured real-time SVS 3-D terrain and HITS flight path symbology. The Navigation Display (ND) presented a GPS-driven moving map which had the capability to depict the aircraft’s selected course, terrain, obstacles, air traffic and weather data all on the same screen. Initial tests have shown the SV-HITS system provides precision-approach accuracy to course guidance along the entire route of flight, and significantly reduces the chances for CFIT accidents.

Research on SVS and Human Factors

Substantial research is currently being done to evaluate the effectiveness of Synthetic Vision Systems in improving situational awareness, refining aircraft control in low-visibility flight scenarios and reducing or eliminating instances of Controlled Flight Into Terrain. The following example studies focus on slightly different pilot groups and evaluate different facets of pilot performance while using SVS on both a quantitative and qualitative level.

Both studies utilize a simulated Synthetic Vision System as part of their experimental group, each displaying computer-generated 3-D terrain and several using tunnel-in-the-sky guidance. In both studies, use of the SVS system was found to reduce pilot workload, improve aircraft control, and increase situational awareness substantially compared to baseline display systems.

Research Example # 1: Private Pilots

The first investigation was undertaken by Takallu, et al., at the NASA Langley Research Center in Virginia. The focus was on low-time General Aviation (GA) pilots having limited instrument flight skills. A common GA accident scenario involves non-Instrument-rated pilots inadvertently flying from Visual Meteorological Conditions (or VMC, in which the ground and horizon are clearly visible and are used as the primary aircraft course and attitude references) into Instrument Meteorological Conditions (or IMC, in which the ground and horizon are obscured by clouds, fog or haze, and the flight instruments become the primary means of controlling the aircraft’s course and attitude). In such a scenario, the low-time Private Pilot is taught to execute a 180 degree level turn by reference to the instruments in order to hopefully return to visual conditions. Loss of aircraft control or CFIT commonly results.

In this study, 17 GA pilots with Private Pilot, Airplane Single-Engine Land ratings participated. None of the pilots had any instrument training beyond that required for the Private Pilot certificate. The pilots were tasked to evaluate three (3) different instrument display concepts in a flight simulator at Langley’s General Aviation Work Station.

  • Display 1, referred to as the Attitude Indicator (AI) was the baseline display, designed to replicate the standard “six-pack” of round electro-mechanical gauges in the average light plane cockpit.
  • Display 2, referred to as the Electronic Attitude Indicator (EAI) featured an enlarged attitude indicator representative of the current EFIS “glass cockpit” displays found in most commercial and corporate aircraft.
  • Display 3 was called the SVS display, but was identical to the EAI except that instead of the “brown ground-blue sky” depiction of the standard electronic attitude indicator, the SVS featured computer-generated terrain imagery. No tunnel-in-the-sky symbology was incorporated.

Visual cues were also presented in the flight simulator, giving pilots the ability to look out the “window” for attitude references as much as meteorological conditions would permit. Pilot performance parameters such as heading, airspeed, altitude, bank angle and pitch attitude were evaluated on a quantitative basis. Human factors questionnaires were administered after each session, evaluating the pilots’ perceptions of situational awareness on a qualitative basis.

Each flight session was five minutes in length and involved a straight and level flight beginning in VMC and progressing rapidly into IMC. Pilots were expected to maintain aircraft control using visual cues (i.e. out the “window”) while possible, and then transition to the instrument display when visual reference to the horizon was lost. Once IMC was encountered, the pilots were tasked with executing a 180 degree level turn followed by a constant-airspeed climb and a constant-airspeed descent of 1000 feet each, all by reference to the instrument display. Each of the pilots flew four scenarios three separate times, once with each display type.

The results were as predicted: In every one of the scenarios, pilots demonstrated smoother control inputs, smaller and fewer control input errors, and smaller deviations of airspeed, heading and altitude with the SVS display. Interestingly, however, in several cases, such as altitude control, errors were greater with the EAI display than with the baseline AI display, seeming to suggest that simply depicting standard gauges on an LCD screen does little to improve pilot performance.

In addition, pilots overwhelmingly reported a lower workload and improved situational awareness (SA) during flight in IMC with the SVS display compared to the other two. According to the authors, these findings demonstrated that a display which intuitively presents flight-critical data to the pilot and more realistically simulates visual flying cues will lead directly to a reduced level of flying errors, vastly improved SA, and a reduction of loss-of-control and CFIT accidents.

Research Example # 2: Professional Pilots

Arthur, et al. conducted the following experiment in the Visual Imaging Simulator for Transport Aircraft Systems (VISTAS III) at the

NASA Langley Research Center. The hypothesis for this experiment is that “a Synthetic Vision System will improve the pilot’s ability to detect and avoid a potential CFIT compared to conventional flight instrumentation.” The major focus was to test SVS display size configurations that would easily retrofit into existing corporate and airline fleets.

Since the goal of the study was to evaluate the effect of Synthetic Vision of avoiding CFIT, the flight scenarios featured what the authors termed a “rare event” technique, in which an unexpected, potential CFIT incident was incorporated once for each pilot at the conclusion of a series of IMC approach and departure attempts.

The Displays. Three display sizes were evaluated, a Size “A” display that could be retrofitted into existing Primary Flight Display (PFD) slots on Boeing 757-767 aircraft, a Size “D” that would fit in B-777 PFD slots, and the largest was a Size “X” that represented probable display space alloted on future aircraft. Each of the display concepts included a Terrain Awareness and Warning System (TAWS) and a Vertical Situation Display (VSD), which showed a vertical profile of the terrain along the desired course. Both TAWS and the VSD were incorporated into one secondary Navigation Display (ND).

The PFDs incorporated the SVS technology, or the baseline display as appropriate. Six of the PFD concepts used some variation of a Synthetic Vision System. One PFD concept was used as the baseline, and depicted the conventional Electronic Attitude Direction Indicator (EADI) found in most of today’s airline and corporate cockpits. Course guidance on the baseline EADI display was the traditional “flight director” symbology. Guidance on the SVS displays was provided by “Highway-In-The-Sky” symbology.

The Pilots. Sixteen pilots participated in the test, 15 airline pilots and one NASA researcher. The subjects averaged 8200 hours of logged flight experience. The pilots were briefed on the display concepts and participated in a two-hour training session. The “rare event” scenario was not mentioned, although the pilots were expected to maintain separation from the terrain at all times.

The Flight Scenarios. The pilots were tasked with flying a circling approach in IMC to runway 7 at the “terrain challenged” Eagle County Regional Airport in Colorado. At 200 feet above ground level, the pilots were expected to go around and execute a missed approach procedure the led to a nearby navaid. All of the pilots flew the same procedure several times with different displays. The final run for each of the pilots ended with the “rare event” CFIT scenario. In the rare event scenario, the missed approach course was altered in the flight management computer, so that the PFD’s flight director or HITS symbology would provide guidance into the terrain. The pilots were not informed that this run would be any different than the previous.

The Results. As predicted, the users of the SVS displays demonstrated significantly more accurate lateral and vertical tracking of the desired course compared to the users of the baseline EADI display. Twelve of the 16 test subjects flew the CFIT “rare event” scenario with one of the SVS PFDs. All twelve pilots noticed and avoided the CFIT. “On average, pilots with an SVS display noticed the potential CFIT 53.6 seconds before impact with the terrain.” The remaining four pilots flew the CFIT scenario with the baseline display. All four pilots had a CFIT event. Three pilots impacted the terrain and one passed within 58 feet of a mountain peak, unaware of any terrain conflict. In addition, two unplanned CFIT impacts occurred with the baseline display while executing the circling maneuver from base leg to final approach.

This experiment clearly demonstrated the benefit of the Synthetic Vision System in providing better pilot situational awareness, increased accuracy, lower cockpit workload, and more confidence in knowledge of terrain clearance. The rare event scenario illustrated dramatically the advantage of SVS for identifying and avoiding potential CFIT incidents.

Current and Future SVS Applications

In 2003, Chelton Flight Systems (mentioned earlier in conjunction with the Capstone program) received the first FAA certification of a Synthetic Vision System with Highway-In-The Sky technology. The Chelton EFIS-SVS can now be found on a wide range of general aviation aircraft, from the Beechcraft King Air 200 to the Bell 206 helicopter.

Chelton’s EFIS-SVS was also used on Steve Fossett’s non-stop, non-refuelled flight around the world. His aircraft, the GlobalFlyer, was equipped with two of the displays, one used as a PFD and the other as ND.


Chelton Flight Systems EFIS provided Mr. Fossett with critical information on aircraft performance and navigation. It was his primary source for flight instrumentation, providing a real-time moving map perspective along the entire route of flight, along with seamless three-dimensional terrain modeling. Coupled to a three-axis autopilot, the EFIS played a significant role in reducing pilot workload and in keeping the aircraft flying through a steady flow of green rectangular boxes that created a virtual Highway-In-The-Sky, affirming the aircraft was on course. ~ Chelton Flight Systems

Other avionics manufacturers such as Honeywell and Rockwell Collins are getting on board as well. Both companies are offering larger, integrated avionics displays with easily reconfigurable software that can change to suit the aircraft and the operator. Although these systems don’t specifically offer SVS, the new packages are ready to accept the software as soon as it is certified.

Gulfstream’s PlaneView cockpit also offers large LCD displays, and several Gulfstream aircraft have the option of incorporating Gulfstream’s proprietary Enhanced Vision System (EVS), which received provisional FAA certification in late 2002. Gulfstream’s EVS uses an infared sensor to “see” through clouds and fog and depict that image on a head-up display (HUD) in front of the pilot. (Hughes, 2003.)


Reduced visibility is one of the leading contributors to aviation accidents worldwide. Current EFIS and classic “steam-gauge” cockpit displays have proven to be inadequate in providing pilots with accurate situational awareness and terrain avoidance information. With the computing and display technology available today, a more intuitive means of presenting flight critical data must be designed and evaluated.

Synthetic Vision is that means. Laboratory research and flight test programs have proven that SVS-equipped aircraft are safer and easier to fly. The current number of pilot-error accidents due to low-visibility flight is unacceptable and any technology that can contribute to a reduced accident rate should be implemented as soon as possible.


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