Publications

To maintain safe separation of aircraft on the airport surface, air traffic controllers issue verbal clearances to pilots to sequence aircraft arrivals, departures, and runway crossings. Although controllers and pilots work together successfully most of the time, mistakes do occasionally happen, causing several hundred runway incursions a year and, less frequently, near misses and collisions in the United States. With this rate of incursions, it is imperative to have an independent warning system as a backup to the current system. Runway status lights, a system of automated, surveillance-driven stoplights, have been designed to provide this backup function. The lights are installed at runway-taxiway intersections and at departure points along the runways. They provide a clear signal to pilots crossing or departing from a runway, warning them of potential conflicts with traffic already on the runway. Existing FAA-installed radar surveillance is coupled with Lincoln Laboratory-developed algorithms to generate the light commands. To be compatible with operations at the busiest airports, the algorithms must drive the lights such that during normal operations pilots will almost never encounter a red light when it is safe to cross or depart from a runway. A minimal error rate must be maintained even in the face of inevitable imperfections in the surveillance system used to drive the safety logic. A prototype runway status light system has been designed at Lincoln Laboratory and installed at the Dallas/Fort Worth International Airport, where Laboratory personnel have worked with the FAA to complete an operational evaluation of the system, demonstrating the feasibility of runway status lights in the challenging, complex environment of one of the world's busiest airports.

Surveillance information forms the basis for providing traffic separation services by Air Traffic Control. The consequences of failures in the integrity and availability of surveillance data have been highlighted in near misses and more tragically, by midair collisions. Recognizing the importance and criticality of surveillance information, the U.S. Federal Aviation Administration (FAA) in common with most other Civil Aviation Authorities (CAAs) worldwide has implemented a surveillance architecture that emphasizes the independence of surveillance sources and the availability of crosschecks on all flight critical data. Automatic Dependent Surveillance Broadcast (ADS-B) changes this approach by combining the navigation and surveillance information into a single system element. ADS-B is a system within which individual aircraft distribute position estimates from onboard navigation equipment via a common communications channel. Any ADS-B receiver may then assemble a complete surveillance picture of nearby aircraft by listening to the common channel and combining the received surveillance reports with an onboard estimate of ownership position. This approach makes use of the increasing sophistication and affordability of navigation equipment (e.g. GPS-based avionics) to improve the accuracy and update rate of surveillance information. However, collapsing the surveillance and navigation systems into a common element increases the vulnerability of the system to erroneous information, both due to intentional and unintentional causes.

The Los Angeles Basin ADS-B Measurement Trials provided a quantitative assessment of the existing interference environment at 1090 MHz and the surveillance performance of Mode S Extended Squitter in that environment. Redundancy in the measurement equipment and in the flight configurations chosen during the trials provided extensive cross checking capability, and greatly increased the integrity of the results. ATCRBS reply rates as high as 40,000/second above -90 dBm were measured. The corresponding aircraft distribution and 1030 MHz interrogation rates correlated well with these measurements. A wide range of scenarios were captured to measure the airborne and ground-based reception of ADS-B Extended Squitters emitted by airborne sources. Air-to-air ranges of greater than 100 nmi were routinely observed, and comparison with ADS-B MASPS requirements showed that all airborne requirements were met in the scenarios flown. Air-to-ground reception rates were routinely better than the update rates provided by either en route or terminal radars at ranges beyond 150 nmi. Ground-to-air (uplink) performance was adequate to support transmission of ADS-B or other information in broadcast formats within approximately 60 nmi of the ground station. Finally, these measurements are a valuable source of validation and refinement data for the various models used to predict Extended Squitter performance in current and future scenarios.

Weather Hazard Information distribution is a necessary component for a successful system of weather hazard avoidance for aviation. It is a very important component, but not the only one. In order to be successful, a complete set of components must be included in the system: 1) Accurate Conceptual Model (Appropriate models of the physical process responsible for generating the hazard); 2) Production Infrastructure (System of tools [hardware, software and manpower]; the raw data feeds necessary for production of the hazard information and a standardized message format); 3) Quality Control Infrastructure (System of tools [hardware, software and manpower] & data feeds necessary for identifying and correcting erroneous information immediately); 4) Distribution Infrastructure (A method to relay, in a timely manner, only the information pertinent to the specific user); 5) Policies and Procedures (There must be clearly defined expectations of actions required of the users and recipients of the hazard information); 5) Training (The users and recipients as well as individuals responsible for production and quality control of the information must receive initial and recurrent training regarding actions required). ICAO in their Annex 3, Chapter 7 titled, SIGMET Information, Aerodrome Warnings and Wind Shear Warnings [ICAO 19981, describes in part one such system for weather hazard avoidance. ICAO does a good job defining the necessary production infrastructure. ICAO especially has been successful in defining the standardized message format. The format for SlGMETs is described in detail in Annex 3. But, an international organization Such as ICAO is limited in its scope of influence. Quality control of the SIGMET product and the distribution of the SIGMET is, in large part, beyond ICAO’s control. In addition, the actual weather hazard avoidance policies, procedures and training must be accomplished internally by each individual commercial aviation operator. Since each component listed above is directly dependent on the other five for a successful weather hazard avoidance system, Northwest Airlines (NWA) has chosen to attempt to address all six components of the system internally with use of the NWA Turbulence Plot System (TPS) [Fahey et. al. 2000].

The Federal Aviation Administration (FAA) is currently embarking on programs, such as the Terminal Doppler Weather Radar (TDWR) and Integrated Terminal Weather Systems (ITWS), that will significanlty improve the aviation weather information in the terminal area. For example, TDWR data will be available at 47 airports across the United States that have high traffic and significant risk of wind shear. The TDWRs automatically report microburst, gust front and precipitaion near the airport to air traffic control personnel on a 24-hour basis. Given the great increase in the quantity and quality of terminal weather information, it is highly desirable to provide this information directly to pilots rather than relying on voice communications. Providing terminal weather information automatically via data link will enhance pilot awareness of weather hazards and lead to more efficient utilization of aircraft. It may also decrease air traffic controller workload and reduce ratio frequency congestion. This report describes work performed in 1995 to provide direct pilot access to terminal weather information via an existing data link known as ACARS (Aircraft, Communication Addressing and Reporting System). More than 4000 aircraft operate in the United States with ACARS equipment. During 1995, five Lincoln-operated testbeds provided near real-time terminal weather information to pilots of AFCARS-equipped aircraft in both text and character graphics formats. This effort follows earlier successful demonstrations during the summers of 1993 and 1994. Section 2 of the report describes the TWIP message formats, Section 3 discusses the 1995 operational demonstration, and Section 4 presents TWIP software design. Section 5 provides case analyses from the 1995 demonstration, Section 6 discusses future work, and Section 7 is the summary.