Assessment of Guidance and Surveillance Quality of The Transportable Transponder Landing System (TTLS)

Scott Gondek, Jon Roth, Doyle Peed, Steve Jones, David Quinet and Ben Kuehn

Abstract:	The RhinoTM Transportable Transponder Landing System (TTLS) was designed as a tactical military version of the civilian Transponder Landing System (TLS) by Advanced Navigation & Positioning Corporation (ANPC). The TTLS is an autonomous, field deployable air traffic control precision landing aid that determines the location of an aircraft by interrogating the aircraft transponder and resolving the transponder's location in azimuth, elevation angle, and range through measurements provided by two Angle-of-Arrival (AOA) sensors. The Rhino can provide surveillance to participating Mode 3 aircraft out to a distance of 20 nautical miles. The system can also provide precision guidance to a tracked aircraft. Guidance is available to the aircraft in two different modes, PAR/GCA and ILS emulation. In the first mode of operation, the system presents a standard PAR display format to the system operator enabling the controller to complete conventional ground controlled approaches (GCAs). In the second mode of operation, the system is able to emulate an ILS approach aid for one aircraft at a time. All indications in the cockpit are similar to those received during a normal ILS approach. The evaluation of the TTLS technology was completed using a combination of vendor demonstrations (completed in March and December 2003) and two government-facilitated Limited Technical Assessments (LTAs) conducted in April, May and September 2004. The April and September 2004 assessments, known as LTA Phase I and Phase III, were completed using Marine Corps tactical aircraft and Marine air traffic controllers. LTA Phase II (May 2004) was completed using an aircraft provided by Ohio University's Avionics Engineering Center outfitted with calibrated receivers and a ground based truth referencing system, and ANPC controllers. LTA Phase I was conducted in Yuma, Arizona during the semi-annual United States Marine Corps (USMC) Weapons and Tactics Instructor Course. LTA Phase II was conducted in Madras, Oregon, which was a previous demonstration site approved by the Federal Aviation Administration (FAA) and was located in close proximity to the vendor. LTA III was conducted at Marine Corps Aux Landing Field (MCALF) Bogue, NC and evaluated those modes of operation that were not adequately evaluated during the previous two phases. This paper presents the flight measurement results from the LTA Phase II flight inspection, as well as operational results from LTA I and III. The flight inspection results show that the system is capable of providing Instrument Landing System (ILS) approaches down to International Civil Aviation Organization (ICAO) Category I minimums once a proper installation is completed and calibration procedures performed. The localizer guidance (lateral) meets the Category I signal-in-space requirements for both the main and reciprocal runways. However, there are some problems with the original Multipath Limiting Antenna (MLA) - High Zenith Antenna (HZA) configuration on the Elevation Sensor Assembly (ESA). This particular antenna configuration results in unacceptable vertical linearity and structure roughness. However, the glide slope (vertical) guidance meets the Category I signal-in-space requirements for the main runway if the MLA-HZA is replaced with a dB-5100 antenna. The performance of glide slope guidance accuracy for the reciprocal runway was not completely evaluated due to scheduling constraints. However, given the improvement in glide slope accuracy for the main runway with the dB-5100 antenna in the ESA high antenna position, similar improvements should occur for the reciprocal runway. Similarly, the system is capable of supporting individual talk down Ground Controlled Approaches (GCAs). During a demonstration in December 2003, four simultaneous approaches (one ILS and three GCAs) were observed. During the Flight Inspection, one area controller and two final controllers were used for approach and surveillance operations. Both on- and below-path GCA performance for the main and reciprocal runway was achieved. The aircraft arrived at the missed approach point (MAP) aligned with the runway and at the proper altitude to make a safe landing. The analysis results for surveillance mode operation indicate that the range and bearing accuracy requirements are met but the altitude requirement is at the limit. This was probably caused by a change in barometric pressure during the sortie, which was not properly updated in the TTLS Base Station software. In addition to the MLA performance, operational issues with dropped tracks, initialization time and calibration were noted. 93.3% of the dropped tracks were due to missing measurements with the remainder due to expected operation. Missing measurements and initialization time are all dependent on the interrogation scheme - which includes the interrogation rate and suppression scheme - and the capability of the software algorithms. These are addressed through further analysis in an Interrogation Method Trade Study conducted by ANPC that provides the optimal interrogation scheme and algorithm improvements. The LTA I and III results show that the precision approach capability to both ends of the runway was demonstrated reasonably well for all types of aircraft tested, and approximately 50 flight hours were logged during the three test events. Although track drops occurred during the instrument approach profiles, the system was generally able to re-acquire tracks to facilitate providing approach guidance to the aircrew. In addition, TTLS tracked up to eleven aircraft simultaneously while in the surveillance mode. Aircraft tracks were observed from 100 feet up to 39,000 feet above MSL and targets were tracked from directly overhead the system out to 20 NM miles in all directions. The TTLS proved to be sufficiently self transportable during the evaluation by demonstrating the ability to traverse undulating and uneven terrain without difficulty or creating any operations or maintenance problems for the system. Installation of the system was straightforward and generally conformed to the written instructions and training provided by the vendor. The set-up times steadily improved over the course of the evaluation from a high of twelve hours to a minimum time of six hours by the end of the evaluation period. The disassembly times improved from five hours to three hours. Improvements to the calibration process were also evaluated using a calibration procedure that did not require any additional ground based equipment (i.e. theodolite). This procedure was promising but will require additional software tool support and further evaluation.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	617 - 628
Cite this article:	Gondek, Scott, Roth, Jon, Peed, Doyle, Jones, Steve, Quinet, David, Kuehn, Ben, "Assessment of Guidance and Surveillance Quality of The Transportable Transponder Landing System (TTLS)," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 617-628.
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