A system to help prevent runway incursions is being integrated into a synthetic vision system (SVS) to provide perhaps the ultimate in situational awareness to air transport pilots as they land, take off and taxi at airports. The combined package, developed by NASA’s Langley Research Center in Virginia, has been installed in the agency’s Boeing 757 and a flight simulator, and is set to be tested.
The system to be flight tested is the result of an effort that NASA launched in 1993. That project led to the first prototype of NASA Langley’s Runway Incursion Prevention System (RIPS), tested two years later in the agency’s B737 (now in the Museum of Flight in Moses Lake, Wash.). In 1993 a dramatic upsurge in runway incursions reported by the Federal Aviation Administration (FAA) also began–from 186 that year to 431 in 2000. And the problem has not subsided; in mid-September FAA reported that 308 airport surface incidents and accidents had occurred so far this year.
Designed to prevent runway incursions in any visibility condition, the RIPS is intended to provide the following:
Ownship position awareness, or where you are;
Traffic position awareness, or where others are;
Taxi route awareness, or where to go;
Route deviation detection; and
Runway incursion detection and alerting.
The RIPS combines a head-down moving map display, a head-up display (HUD) that gives pilots real-time surface-movement guidance, processing hardware, and application software. Should an aircraft still wander off course, the system gives pilots audible and visual route deviation alerts. The RIPS also uses positioning data from onboard systems. During test flights in 1997 at Hartsfield Atlanta airport, and in 2000, at Dallas-Fort Worth airport (DFW), the RIPS used ground-based positioning data from technology developed by FAA’s Runway Incursion Reduction program.
Head-Down Display
The electronic moving map display shows the airport layout, derived from a Jeppesen database, and the ownship position, fed by an inertial navigation system (INS) integrated with a differential GPS receiver. The INS helps produce "smoother updates" than differential GPS alone, which generates an update each second, according to Denise Jones, research engineer at NASA Langley.
The controller’s instructions for taxiing appear in text form at the bottom of the moving map display in pop-up windows that the pilots can remove if desired. And they appear in graphic form–thanks to the RIPS’ onboard graphics software–to show the approved taxi route (in magenta) and hold-short locations (as yellow and red bars) on the moving map.
For the test flights at DFW, NASA Langley worked with Ohio University to develop a voice recognition system that converts a controller’s aural instructions to data, which was transmitted to pilots via VHF Mode 2 data link (VDL-2), establishing controller pilot data link communications (CPDLC). In the absence of CPDLC, pilots could input the taxi route data using a keyboard–though Jones stresses that obtaining route data from controllers is better, as it reduces pilot workload.
Traffic on the moving map is shown as circles when other aircraft are traveling less than 8 knots, which is too slow to obtain accurate heading information. When other aircraft are moving faster than 8 knots, the circles convert to chevrons that indicate their headings. Either the airline and flight number or aircraft type accompanies both symbols. The aircraft symbols are color-coded as well, to show which aircraft are on the ground (dark blue) and which ones are flying (cyan).
Traffic Data
Traffic information can come from automatic dependent surveillance-broadcast (ADS-B) data transmitted by other aircraft and surface vehicles and from traffic information services-broadcast (TIS-B) data transmitted by ground-based equipment, such as airport surface detection equipment (ASDE-3) radar, a multilateration system, and/or an airport target identification system (ATIDS). During initial RIPS testing at DFW, NASA’s B757 received data from different ground-based sources. An algorithm in the airport’s surveillance system fused the data, providing a complete picture of surface traffic.
Other sources of traffic data also may be included in the RIPS. NASA Langley engineers still are exploring various options for the system. "For example, we’re developing algorithms to use an airborne weather radar for runway object detection," says Jones. "In this case, we have algorithms that ‘look’ at the radar scan and determine the position of objects on the runway. This data will be fused with other traffic position data on board the aircraft."
Jones foresees the use of the different traffic data sources, depending on the airport facility. "I would envision that traffic information from surface sources will occur at major airports," she says. "But by using ADS-B, aircraft could be more autonomous and operate at airports with limited ground equipment."
The HUD
Information presented on the RIPS head-down display also appears on the pilot’s HUD. But instead of a magenta line on an airport map, cones appear on the HUD, forming a path for the aircraft to follow. Flight Dynamics provided the RIPS HUD and is developing its surface guidance system, based on NASA research.
The standard Flight Dynamics HUD employs stroke graphics, which creates sharp, bright symbols, says Jones. However, NASA Langley has combined this graphics software with raster graphics (scanned line by line) for the purpose of generating synthetic vision imagery of terrain on the HUD.
Detection and Alerts
To further protect aircraft from possible conflicts due to surface traffic, the RIPS also includes runway incursion detection and alerting during approach and landing, takeoff roll and taxi crossing.
NASA Langley has been evaluating two different incursion detection algorithms during simulation study and flight testing. Lockheed Martin, an on-site contractor, produced one set of algorithms. Under a cooperative research agreement, in which NASA covered 50 percent of the development costs, Rannoch Corp. produced the other set. By partnering with a private company, Jones says, NASA hopes to "accelerate of the commercial use of the RIPS."
The RIPS algorithms do not provide maneuver guidance for taking evasive action. However, the alerts they generate can be shared with air traffic controllers via a data link. Onboard processing also demonstrated that it could provide pilots with more timely alerting than the transmitted, surface-generated alerts. This was discovered during the DFW testing, in which four airline captains flew 47 test runs.
Once the onboard algorithms detect an incursion, the flight crew is given both audible and graphical alerts. The recorded audible alerts for incursions are "Runway Conflict!" and "Runway Traffic!" As the audible alert is broadcast, the traffic symbol and ID tag of the aircraft that is causing the conflict are highlighted on the head-down display. In addition, the words, "Runway Conflict" or "Runway Traffic," along with a target designator box outlining the intruding aircraft, appear on both the head-down display and HUD. During simulations, Jones says, NASA personnel observed that, logically, the non-flying pilot would use the head-down display, while the flying pilot uses the HUD. The RIPS also alerts the flight crew if an active hold line is crossed ("Crossing Hold!") and if the aircraft deviates from its assigned taxi path ("Off Route!").
An Integrated System
Currently, the various RIPS components–moving map, HUD imagery, etc.–are run by separate PCs that communicate through a ScramNet data network. "In the future, for commercial use, these systems would be integrated with systems in the aircraft," Jones explains. Also, in commercial aircraft, the RIPS head-down display could be shown on a navigational display, multifunction display (MFD), or electronic flight bag (EFB), she adds.
NASA testing of the RIPS at Dallas-Fort Worth airport was part of the agency’s Aviation Safety Program. In addition to its modern traffic surveillance system, the airport had a ground station installed to give differential corrections to the GPS signal.
From the flight tests, NASA engineers were able to develop enhancements for the RIPS algorithm and display, which, in 2002, were evaluated in NASA Langley’s Research Flight Deck (RFD) simulator. Over the past year, the RIPS and NASA Langley’s synthetic vision system have been jointly integrated and tested in the agency’s Integrated Flight Deck (IFD), which emulates the B757 cockpit.
The SVS
NASA’s synthetic vision system combines GPS signals, a three-dimensional terrain database, and information from advanced sensors, such as weather radar, ADS-B and a traffic alert collision avoidance system (TCAS), to provide a clear electronic picture of the view ahead, regardless the weather or time of day. The SVS imagery appears on the HUD and both the primary and navigation displays. An "egocentric" view (as if looking out the cockpit) appears on the primary flight display, while an "exocentric" view (as if looking from outside the aircraft) is shown on the nav display.
Flight Testing
In August and September 2001, the SVS system alone was evaluated in test flights in and out of Colorado’s Eagle County Regional Airport, near the Vale ski resort. Though a launch date has not been set, the agency’s B757 is equipped and ready for flight tests of the RIPS-SVS combination, to be conducted at Reno (Nev.) airport and NASA’s Wallops Flight Facility in Virginia.
Reno was selected because it is "terrain-challenged," says Jones, referring to the nearby Sierra Nevada Mountains. "The synthetic vision researchers are interested in testing in that environment." For the RIPS, Reno airport presents the challenge of operating where runways cross. "This adds a new situation to the mix," Jones adds.
"At the Wallops facility the focus will be on runway incursion because we have more control of the environment," Jones explains. "We will use ADS-B-equipped vehicles in the terminal area to serve as incurring traffic."
Simulation tests will accompany the flight tests, providing the opportunity for more rigorous evaluation of the combined systems. "We want to conduct some ‘rare event’ testing, in which the pilot would encounter an incursion infrequently, so he doesn’t expect it," says Jones. "This way we will test the system under more realistic circumstances."
"The simulation tests and flight testing will not be parallel," she adds. "They will feed each other."
Facts About Runway Incursions
The FAA has sifted through its statistics of runway incursions and discovered some enlightening facts about the problem, including the following:
Weather is not a factor in 89 percent of runway incursions.
Pilots taxiing onto runways or taxiways without clearance account for 62 percent of cases.
Pilots landing or departing without clearance account for 23 percent of cases.
Pilots landing on the wrong runways account for 10 percent of cases.
Pilot distractions account for 17 percent of cases.
Pilots are disoriented or lost in 12 percent of cases.
Pilots’ unfamiliarity with ATC procedures or language accounts for 22 percent of cases.
Pilots’ unfamiliarity with the airport accounts for 19 percent of cases.
General aviation aircraft are involved in 69 percent of all cases.
Low-time pilots (less than 100 hours) account for 32 percent of all runway incursions.
High-time pilots (more than 3,000 hours) account for 10 percent of the runway incursions.
The top five aircraft involved in runway incursions are all single-engine, general aviation airplanes.