AILS

AIRBORNEINFORMATIONfor LATERALSPACING

Flight-deck Centered Technology to Enable Closely-spaced Parallel Approaches in Instrument Meteorological Conditions

Overview	AILS Studies
Background	Research Plans
Concepts	Bibliography and Related Works

Overview

Airborne Information for Lateral Spacing (AILS) is an effort within the Reduced Spacing Operations (RSO) element of the Terminal Area Productivity (TAP) Program at NASA. The objective of the AILS research being conducted at the Langley Research Center and at the Ames Research Center is to enable approaches to closely spaced parallel runways in Instrument Meteorological Conditions (IMC) with a capacity similar to that obtained in Visual Meteorological Conditions (VMC). This research is examining options to enable airborne crew responsibility for aircraft separation during closely spaced parallel approaches. The initial focus of the NASA work has been on independent parallel approaches with intentions of investigating dependent concepts as time and resources permit.

Langley and Ames have planned a number of studies to address the problem, with Langley leading in this activity. A concept design team has been assembled to address the problem. The team at Langley has designed an initial concept after concluding that the problem of flying parallel approaches has two major components. The first is to provide accurate navigation for aircraft on the closely spaced parallel approach paths and to provide alerts to help keep intrusions from occurring. The second is to provide adequate protection for aircraft should one aircraft deviate from its assigned airspace in a manner that threatens another aircraft on a parallel approach path. The research at Ames has focused on providing TCAS like display guidance during collision avoidance maneuvers. The AILS work to date has addressed parallel pairs as opposed to parallel triplets or quadruplets, since it presents a simpler, yet real problem with significant payoff potentials.

The figure above illustrates technology that could potentially be used to implement the concept. Differential Global Positioning Systems (DGPS) is assumed to provide the basis for the accurate navigation required to perform the approach, while Automatic Dependent Surveillance-Broadcast (ADS-B), currently under development, will enable aircraft to broadcast their position and other state information such as track and rate of turn. Other aircraft will receive the transmitted information and maintain an accurate fix on aircraft operating on a parallel approach. In addition, the transmitted state information will provide an indication of whether the traffic is turning away from its course or headed back to its nominal path.

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Background

Problem Statement:

Many U.S. airports depend on parallel runway operations to achieve capacity necessary for day to day operations. In the current airspace system, instrument meteorological conditions reduce the capacity of parallel runway approach operations spaced closer than 4300 ft. apart, or 3400 ft. where Precision Runway Monitoring (PRM) is applicable. The lost capacity costs the airline industry hundreds of millions of dollars each year. Its impact on other businesses and personal inconveniences to travelers is significantly costly but difficult to quantify.

Domestic Airports with Closely-Spaced Parallel Runways

Parallel Runways List

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Concepts

As mentioned above, this concept focuses on two aspects of the problem. One aspect is to provide accurate navigation to keep aircraft in their own assigned airspace along the approach paths and keep aircraft from threatening others. Langley engineers are investigating whether the conventional localizer path can be replaced with capabilities such as DGPS to provide parallel approaches where there is less potential for path overlap. Langley is currently exploring use of an alternate "localizer" profile based on precision navigation capabilities such as DGPS. The two dot localizer deviation profile is shown in the figure below and was suggested by a member of the concept design team. In the area of "localizer capture," the two dot deviation is 2000 ft. on either side of the extended runway centerline. Also, as is normal for parallel runway operations, the approach paths are separated by 1000 ft. altitude during localizer capture. At about 12 miles from the runway threshold, the path width begins to taper down to 400 ft. on either side of the extended runway centerline at 10 nautical miles. After the 400 ft. half-width area is entered, the higher aircraft starts to descend and altitude separation is given up. The 400 ft. half width of the path is held from that point to a location near middle marker where a conventional localizer angular beam shape and width are captured (using DGPS to emulate the conventional localizer signal).

Another concept under investigation is to employ an ILS look-alike profile in which one or both approach centerlines are skewed or rotated slightly from the extended runway centerline such that the 'two-dot' path boundaries do not overlap. Note that such an approach could not be used for Cat III landings.

An alerting feature has also been incorporated in the concept to prevent aircraft from straying from their airspace. Should an airplane deviate one dot or more from its nominal path, a caution or level two (SAE ARP-450D) alert is issued to the deviating aircraft with displayed information presented in amber alphanumeric and symbolic formats in the primary flight display and in the navigation display, to warn the flight deck crew to maintain a tighter path adherence. Should an aircraft deviate two dots or more from the prescribed path, a level three alert is issued (using red colors for the displayed information), requiring a break-off maneuver in the direction away from the parallel traffic. In the version of the Langley concept implemented for the second phase of testing, depending of the severity situation, level two or level three alerts are also used to prevent one aircraft from threatening another with excessive bank angles or tracks. The current Langley concept requires use of a single, identical break-off maneuver for all parallel approach deviations. The aircraft required to break off the approach must execute an emergency escape maneuver consisting of a turning climb to a heading 45 degrees away from the nominal runway heading, in the direction away from the parallel approach traffic. A heading bug is automatically set to the (45 degree) escape heading when the alerting algorithms are armed in the approach sequence.

The second aspect of the Langley version of the AILS concept addresses procedures to avoid collisions and near misses in the event one aircraft strays from its airspace and approaches the path of another in a threatening manner. An onboard alerting algorithm will use state information from traffic on the parallel runway, transmitted by the ADS-B link, to detect threatening aircraft and provide an onboard alert to the flight deck crew. The alert is again presented in the primary flight display and the navigation display. A caution is presented in amber as the alerting system first detects the threat as it starts to evolve. As the danger becomes more imminent based on the computations associated with the alerting algorithms, a red (level three) alert is issued in the flight deck of the protected aircraft. The (amber) caution alert and the (red) warning alert in the configurations under study at Langley are accompanied by specially designed displays of the threatening airplane’s path to allow the flight deck crew to quickly assess the nature and severity of the threat. In the concept, the red alert, a level three, requires the flight deck crew to execute the emergency escape maneuver as described above. Again this is an immediate, accelerating, climbing turn away from the approaching traffic and parallel runway to a heading of 45 degrees from the nominal approach heading. The version of the concept under study at Langley displays information in the primary flight display and in the navigation display. A computer controlled voice message complements the displayed information with a "Turn, Climb. Turn, Climb. Turn, Climb" aural advisory when the level three alert is activated.

Illustrations: Nominal Display Graphic / Localizer Deviation Caution / Traffic Warning Alert

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NASA Workshop (October 1996)

A Government and Industry Workshop on Flight-Deck-Centered Parallel Runway Approaches in IMC was conducted October 29, 1996 at the NASA Langley Research Center, Pearl I. Young Theater. The document Proceedings of the NASA Workshop on Flight Deck Centered Parallel Runway Approaches in Instrument Meterorological Conditions, NASA Conference Publication 10191, December 1996, contains the slides and records of proceedings at the workshop. The purpose of the workshop was to disclose, to the national airspace community, the status of ongoing NASA Research and Development (R&D) to address the closely spaced parallel runway problem in instrument meteorological conditions and to seek advice and input on the direction of future work to assure an optimized research approach.

The workshop highlighted results of focused NASA R&D to develop a practical solution to IMC approaches to closely spaced parallel runways. NASA simulation studies have shown promising results for parallel approaches spaced as close as 1700 ft. apart. Implementation in the field will require capabilities such as will be provided by ADS-B and local DGPS. The intent of this R&D is to provide a concept that will complement the capabilities developed in the FAA’s PRM program, to safely accomplish even closer parallel runway approaches. The technology envisioned includes enhancements to current Traffic Alert and Collision Avoidance System (TCAS) technology and navigation capabilities in the flight deck to enable airborne crews to assume responsibility for lateral path compliance and separation during closely spaced parallel approaches.

As of October 1996, NASA had completed three simulation studies and has scheduled initial flight testing to further develop and evaluate related technologies. These studies and plans where discussed by Marvin Waller of Langley, Trent Thrush of Ames, and Charles Scanlon of Langley.

The workshop also included a discussion by Rocky Stone of United Airlines (UAL) of plans to explore the use of dependent parallel approaches described as "paired approaches." This concept was first investigated at NASA Langley in 1994 and discussed in a presentation to RTCA SC-147 in June 1995 (Ref. RTCA Paper No. 346-95/SC147-634, July 14, 1995), as a "Staggered Pair Concept." The adaptation by United Airlines has added cooperating pairs of company airplanes to address the delay dilemma at the San Francisco International Airport (SFO) where the parallel runway separation is 750 feet. Rocky Stone is leading the effort at UAL.

In a presentation describing work closely related to AILS, Gene Wong, FAA AND-450, presented a discussion of the status of the FAA PRM Program that has been successful in enabling close parallel runway operations down to 3400 feet lateral runway spacing. Also, David Hinton of NASA Langley discussed NASA’s plans to investigate the implications of wake vortices on closely spaced parallel runway operations in IMC.

The Table of Contents from the workshop proceedings document is shown below:

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AILS Studies

In interpreting the study results it is important to realize that they show the feasibility of the AILS concept in initial testing in a research simulator environment and that a large amount of additional testing and validation is required before a concept of this nature could be implemented in the national airspace system. Among the issues that must be resolved is the effects of wake vortex considerations.

LaRC 3400' & 2500' Runway Spacing

The concept design team at Langley completed a fixed base simulation test of the initial concept in May 1996. In the test, sixteen pilots each flew 56 parallel approaches, with about one third of the cases presenting collision or near miss threats. The test subjects were line pilots from a number of airlines and air-freight companies. They were trained for the task as they are trained and tested for other critical situations (e.g., rejected takeoffs), and for category II approaches. The reaction time of the pilots in executing the turning maneuver and the distance at closest approach were key parameters measured in these tests. Parallel approaches spaced 3400 and 2500 feet apart were examined in the initial study. The test findings show that, under the conditions tested, all of the pilot reaction times were well under the two seconds targeted by the NASA design team, and that no trials resulted in violations of the 500 ft. minimal separations used for defining near misses in the parallel runway approach environment. The mean miss distance measured was in access of 1900 ft., with the closest encounter of 1183 ft.

ARC 4300' & 2500'

The study at NASA Ames Research Center was completed in August 1996 and compared an MIT-derived Alternate Alerting System (AAS) and traditional TCAS concepts in the closely spaced parallel runway approach environment. This study showed that a display based on the TCAS formats, but enhanced with a higher resolution navigation display and specially designed alerting algorithms, resulted in better performance than the TCAS implementation using a conventional navigation display format. The performance with the enhanced display features and alerting algorithms resulted in no near misses and good pilot evaluations. The study at Ames investigated an autopilot coupled approach, in contrast with the manual mode used in the Langley studies, and addressed the 4300 ft. and 2500 ft. runway spacing cases.

LaRC 1700' & 1200'

A second phase of testing was completed in July 1996 at Langley. The follow-up tests included new alerting algorithms and modifications to the displays based on observations and pilot comments from earlier tests. Runway lateral spacing was reduced to 1700 ft. and 1200 ft. Eight two-member airline crews were tested in the second phase. The results were very promising for the 1700 ft. runway separation, with no encounters closer than the targeted 500 ft. miss criteria. The 1200 ft. case resulted in one encounter closer than the 500 ft. two dimensional near missed criterion used and is regarded as questionable by the design team, when the current experimental AILS technology is used.

B737 Performance Flight Test

A flight test of the lateral path management accuracy aspect of AILS was completed in the NASA B737. The pilots flew 10 NM final approaches using the + 400 ft 2 dot course deviation of the AILS process, in moderate turbulence. The result was that during 99.7 percent of the time the flights were within one dot (+200 feet) lateral course deviation. The pilots had no difficulty flying the final approach with the more sensitive AILS course deviation indicator program.

ATC Integration

One of the recommendations made to NASA by the workshop participants was that more effort be put into developing the ATC aspect of the AILS concept. In response to that recommendation NASA formed a team to study the ATC related requirements of AILS. The draft document Analysis of the Role of ATC in the AILS Process represents the status of the efforts of that team to date.

Candidate Airports for AILS Technology

A number of airports in the country were surveyed to provide a single source of information for research to determine airports where AILS technology may be applicable. The resulting report Air Traffic and Operational Data on Selected U.S. Airports With Parallel Runways (.pdf format) focuses on airports that have at least one pair of parallel runways closer than 4300 ft. Information contained in the report describes the airport's current operational activity as obtained through contact with the facility and from FAA air traffic tower activity data for FY 1997.

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Research Plans

AILS Requirements and Goals

In developing the AILS concept, NASA Langley is working to understand and provide the information airborne crews require to maintain safe separations during closely-spaced approaches. Specifically, the following three requirements are being addressed to successfully develop and demonstrate the AILS concept:

Develop, test, and demonstrate techniques to improve navigation precision of aircraft on closely spaced parallel approaches so the probability of an intrusion is reduced.

Develop, test, and demonstrate conflict detection, alerting, and appropriate displays necessary to prevent a near miss in the event of an intrusion from an adjacent parallel approach were to occur.

Develop, test, and demonstrate AILS/ATC integration procedures to clear aircraft to conduct AILS approaches and re-accept lateral separation responsibility in the event of an evasive maneuver or missed approach.

The specific goal of the NASA Langley AILS research is to determine, test, and verify the minimum implementation of AILS necessary to support independent instrument approaches under IFR to runways spaced 2500 feet apart runway centerline to runway centerline in Category I weather conditions (Baseline AILS). A secondary goal of the AILS research, resources permitting, is to investigate, test, and verify additional solutions for runways spaced closer than 2500 feet apart, such as segmented approaches, offset approaches, and paired-staggered approaches (Enhanced AILS).

Planned Research Approach and Studies

AILS Schedule and Accomplished Milestones

More details of the Langley Research Center AILS concepts are presented in the draft reports (.pdf format) The Flight Deck Perspective of the NASA Langley AILS Concept and Analysis of the Role of ATC in the AILS Process.

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NASA Program Information

Contacts at Langley Research Center

Name	Phone	E-Mail
Brad Perry	(757) 864-8257	Raleigh.B.Perry@LaRC.NASA.GOV
Terry Abbott	(757) 864-2009	T.S.Abbott@LaRC.NASA.GOV
Marvin Waller	(757) 864-2025	M.C.Waller@LaRC.NASA.GOV

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Development Team & Participants

This list represents a partial list of the government agencies, universities, contractors, and other participants in the AILS development:

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Bibliography of AILS Publications

Abbott, Terence S. and Elliott, Dawn M.: Simulator Evaluation of Airborne Information for Lateral Spacing (AILS) Concept (.pdf format), NASA/TP-2001-210665, March 2001, 71 pages (407KB).

Hemm, Robert and Shapiro, Gerald: Airborne Information for Lateral Spacing (AILS) Benefit Estimate (.pdf format), Logistics Management Institute report NS906S1 for NASA contract NAS2-14361, November 1999, 108 pages (1,855KB).

Waller, Marvin C. and Scanlon, Charles H.: A Simulation Study of Instrument Meteorological Condition Approaches to Dual Parallel Runways Spaced 3400 and 2500 Feet Apart Using Flight-Deck-Centered Technology (.pdf format), NASA/TM-1999-208743, March 1999, pp. 104, (796KB).

LaRC AILS Team: The Flight Deck Perspective of the NASA Langley AILS Concept , Draft Report, October 1998.

Winder, L.; and Kuchar, J. K.: Evaluation of Vertical Collision Avoidance Maneuvers For Parallel Approach (.html), Presentation at the AIAA Guidance, Navigation, and Control Conference, Boston, MA, August 10-12, 1998.

Doyle, Thomas; and McGee, Frank: Air Traffic and Operational Data on Selected U.S. Airports With Parallel Runways (.pdf format), NASA/CR-1998-207675, May 1998.

Waller, Marvin C.; Doyle, Thomas; and McGee, Frank: Analysis of the Role of ATC in the AILS Process (.pdf format), Draft Report, May 1998.

Jackson, Mike: Description of AILS Alerting Algorithm (.pdf format), Honeywell Technology Center, Minneapolis MN, September 29, 1997.

Kuchar, J. K.; and Carpenter, B. D.: Airborne Collision Alerting Logic for Closely-Spaced Parallel Approach, Air Traffic Control Quarterly, Vol. 5, No. 2, 1997.

Carpenter, B. D.; and Kuchar, J. K.: A Probability-Based Alerting Logic for Aircraft on Parallel Approach, NASA CR-201685, April, 1997.

Carpenter, B. D.; and Kuchar, J. K.: Probability-Based Collision Alerting Logic for Closely-Spaced Parallel Approach, AIAA Paper 97-0222, AIAA 35th Aerospace Sciences Meeting, Reno, NV, January 6-10, 1997.

Waller, Marvin C.; and Scanlon, Charles H.: Proceedings of the NASA Workshop on Flight Deck Centered Parallel Runway Approaches in Instrument Meteorological Conditions.; NASA CP 10191, December 1996.

Koczo, Steve: Coordinated Parallel Runway Approaches, NASA CR-201611, October 1996.

Pritchett, A.; Carpenter, B. D.; Asari, K.; Kuchar, J. K.; and Hansman, R. J.: Issues in Airborne Systems for Closely-Spaced Parallel Runway Operations, Proceedings of the 14th AIAA/IEEE Digital Avionics Systems Conference, Cambridge, MA, November 1995.

Ebrahimi, Y. S.: Parallel Runway Requirement Analysis Study, Volume 2 - Simulation Manual, NASA CR-191549, December 1993.

Ebrahimi, Y. S.: Parallel Runway Requirement Analysis Study, Volume 1- The Analysis, NASA CR-191549, December 1993.

Links to Related Documents and Presentations

Doyle, Thomas: Presentation to MSP ATC Management (.pdf format) text and view graphs, November 3, 1998.

Waller, Marvin C.: Presentation to RTCA SC-186 WG1, May 14, 1998 (.pdf)

Waller, Marvin C.: Presentation to ATM ESC, May 13, 1998. (.pdf)

Other (Non-AILS) Documents

Precision Runway Monitor Program Office (FAA): Precision Runway Monitor Demonstration Report, DOT/FAA/RD-91/5, February 1991.

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Responsible NASA Official: Raleigh B. Perry ( 757-864-8257 )

Updated March 15, 2002

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