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Russ College of Engineering and Technology
Avionics Engineering Center
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MLS Research Capabilities

Avionics Engineering Center (AEC) personnel have extensive MLS/MMLS experience in multipath modeling, field/flight measurement, site surveys, system installation, signal modeling, equipment procurement, and seminar development. These capabilities are discussed briefly below.

  1. Multipath modeling for developing /refining MLS siting criteria, estimating installed-system performance at a specific site(s), and performing general assessment of antenna design(s).

    The AEC was involved in the refinement and validation of the MLS Mathematical Model that has been developed by the Federal Aviation Administration. This model can provide Path Following Error (PFE) and Control Motion Noise (CMN) estimates along user-specified flight paths, as well as multipath diagnostic information. The model takes into account the multipath generated due to signal reflection, diffraction and/or shadowing by buildings, aircraft and/or terrain for up to fourth-order ray paths. Since 1984, AEC personnel have performed over 50,000 simulations using this model, and it remains in active use today. The model can be modified easily to provide equipment-specific performance estimates.

  2. MLS/MMLS flight measurements for engineering (equipment design) and operational performance (flight inspection) assessments.

    AEC facilities include: an MLS test aircraft (Piper Saratoga); an airborne data-collection system with data link; four-dimensional, ground-based, optical truth-reference system with data link (a kinematic differential GPS truth system is also available); data-collection and analysis software; an MLS test site (azimuth, elevation, DME/P, back azimuth, RMMS); and, IFR-800 and IFR-600 test sets.

    The airborne data-collection system includes: an industrialized computer, a Bendix 201 or 20A (flight-inspection) angle receiver; a Foster 670 DME interrogator; a Motorola Mini-ranger III transponder; special format displays; associated control heads; specialized communication and voice recording equipment; and, a general-purpose printer for generation of quick-look, differential data plots between flight-measurement profiles. When needed, the loan of a DME/P interrogator from the FAA has been arranged and integrated into the data-collection system.

    The data-collection and analysis software is comprised of two modules. The "quick-look" module is a standard part of the airborne data-collection software; it provides azimuth, elevation, and DME/P differential-data plots with flag and frame-counter information. These plots can be generated quickly after each flight-measurement profile (while airborne) and are used for quality control of the flight-measurement process. The Data Reduction and Analysis Software Package (DRASP) is a Windows-hosted program used to generate differential, PFE, CMN, flag, frame counter data plots with tolerance brackets, as appropriate.

    The truth-reference system includes: a joy-stick controlled Warren-Knight theodolite with incremental, optical-shaft encoders and motor drives; a Motorola Mini-ranger III interrogator and reference station; an AEC-designed Ground Data Manager for ground-data fusion and transmission of these data to the airborne data-collection system; and, communication equipment. A portable generator is available and can be used to provide electric power for the truth-reference system at remote locations. Further, the AEC owns a Topcon total station (GTS302) which can be used for establishing equipment locations and any control points needed for the truth-reference system.

    System calibration is monitored through the use of special procedures and the use of AEC-owned IFR-800 (MLS angle) and IFR ATC-600A (DME) test sets. Calibration of equipment by the manufacturer is performed, as required.

    The AEC MLS flight-measurement system has been used for collecting model validation data, validating MLS siting criteria, supporting equipment manufacturer development testing, supporting governmental assessment/acceptance testing, and performing operational system evaluations. Further, AEC personnel played a key role in developing the test plan/procedures for the majority of the testing that has been performed with this flight-measurement system.

  3. Site surveys for determining specific locations for the installation of the MLS subsystems (azimuth, elevation, DME/P).

    AEC personnel were prime in the development and adoption the internationally published MLS critical area criteria, MLS/ILS collocation criteria, MLS/ALS siting criteria, as well as the drafting of the FAA MLS Siting Manual. An internal site-survey handbook has been developed, as well as an installation checklist. This handbook and checklist have been used to perform site surveys for the FAA and US Air Force at over a dozen locations.

  4. Physical installation of MLS equipment.

    AEC personnel have performed at least five "turn-key" system installations to support various research efforts. Due to time and cost consideration, AEC personnel performed the bulk of all the installation work. This work included performing the site survey, obtaining installation approvals and channel assignments from the FAA, preparing the site, shipping and installing the equipment, and performing the pre-commissioning flight check. The most recent activity was the installation of the MLS (approach azimuth, elevation, DME/P, back azimuth, and remote control/status unit) currently sited at the Ohio University airport (UNI), Runway 25. This system is the third system (upgrade) AEC has installed at UNI since 1986. This system was installed to support the assessment of general-aviation pilot performance for curve missed-approach and departure procedures. Thus, the performance of the MLS throughout its coverage volume had to be assessed, in additional to normal considerations involved in establishing the straight-in, centerline approach.

  5. MLS signal (noise) model development and application.

    This type of modeling can be used to aid in airborne-equipment certification. AEC personnel, in coordination with the FAA and the aviation industry, have developed an MLS signal model. This model has been presented to All Weather Operations Panel of the International Civil Aviation Organization for review.

  6. Proposal assessment and equipment procurement support.

    AEC has provided technical advisors to support FAA equipment procurement activities.

  7. Seminars can be provided on any of the above topics.

    AEC personnel have generated material for FAA MLS seminars and have provided seminars for international clients.


Avionics Engineering Center
Russ College of Engineering and Technology
131 McFarland Avionics Building
Ohio University
Athens, OH 45701
Tel: (740) 593-1515

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