Microwave Landing System Research Articles

Nonlinear simulation of flight along wind compensating curved glidepaths

A technique for defining curved glidepath geometries that compensate for some of the undesirable effects of low altitude winds is described. This technique uses an a priori estimate of the wind conditions present at the time of the landing approach to define a suitable glidepath geometry. The results of closed-loop, six degree-of-freedom simulation of a twoengined STOL transport conducting landing approaches on such curved approaches are summarized, and a number of recommendations for future work are made. Contents D evelopments in microwave landing system technology have given rise to the possibility of defining curved precision approach trajectories. Since the early 1970's a considerable amount of work has been carried out on curved approach trajectories defined in the horizontal plane. This new landing aid technology has also made possible curved approaches in the vertical plane (Fig. 1). The literature has occasionally made reference to such trajectories (e.g., the ''ideal descending route of Ling 1). These might be used for constant rate of descent procedures for portions of the approach and a steep initial approach gradually transitioning to a shallow approach for the last segment prior to landing. This paper briefly summarizes the key results of an evaluation of a particular subset of such vertical plane modified approach geometries. [For brevity, such approach trajectories will be referred to as curved glidepath geometries (CGG).] This subset is based on an estimate of the wind conditions present at the time of the approach through an algorithm that compensates for some of the undesirable effects of wind on aircraft, and potentially reduces pilot workload. Preliminary study of the problem from this viewpoint was undertaken by Hindson and Gould2 in 1974. Their results suggested that CGG may be desirable in the presence of wind gradients in order to alleviate pilot workload, particularly for V/STOL aircraft. This was followed by flight test evaluations in the National Aeronautical Establishment airborne simulator in 1975—76, with encouraging results.3 Method The source of Hindson and Gould's proposal was the observation that vertical wind gradients of the horizontal

Automatic helical rotorcraft descent and landing using a microwave landing system

A helical-approach concept is presented for Instrument Flight Rules (IFR) operation of rotorcraft into congested terminal areas where separation from high-speed jet traffic is highly desirable and the airport-precision-approach aid is a Microwave Landing System (MLS). The concept takes advantage of the fact that rotorcraft need not land on the main runway but can operate from a pad that lies on an MLS radial offset from the centerline. The results of 48 flights using a UH-1H helicopter and a research avionics system are presented. Three levels of navigation sophistication were also investigated. It is shown that an approach helix can be contained in a relatively small volume and that being within the Instrument Landing System (ILS) Category II window at a 30-m (100-ft) altitude is not a requirement for a successful hover over a landing pad. Only two of the three navigation systems provided estimates that allowed all flights to descend from hover to touchdown.

An experimental investigation of VTOL flying qualities requirements in shipboard landings

Abstract : This fifth simulation experiment, using the U.S. Navy X-22A variable stability V/STOL aircraft, was undertaken to generate data for the development to flying qualities and advanced flight control system design criteria for the visual shipboard landing task. Since a broad range of flying qualities were simulated, actual landings were not performed because of flight safety considerations. Instead, a discrete three-dimensional position tracking task, presented to the pilot on a Head-Up-Display (HUD), was devised to evoke pilot control and stabilization activity similar to that in the actual shipboard environment. A microwave landing system with precision ranging capability served as the guidance sensor for both the translational rate flight control system mechanizations and for the HUD tracking information. A total of 111 evaluations were performed of various horizontal and vertical translational rate flight control system dynamics. The primary results of the program defined regions of satisfactory and acceptable flying qualities as functions of velocity command gain and the time constant of velocity response. The limits on command gain and time constant for satisfactory flying qualities indicated by this experiment are considerably smaller than those determined in ground simulator experiments. (Author)

System Considerations for the New DME/P International Standard

The International Civil Aviation Organization (ICAO) has completed technical standards for the precision distance measuring equipment (DME/P). The DME/P is an integral element of the microwave landing system (MLS) and will provide the precision ranging function to complement the already standardized azimuth and elevation guidance functions of the system. In 1978 an ICAO meeting concluded that the DME/P should be integrated into the existing standards for the conventional DME (DME/N) as a compatible service. The motivation for this was economic. It was reasoned that a single L-band airborne unit could satisfy the need for both existing enroute and the new precision approach and landing services, thereby avoiding unnecessary duplication of on-board ranging equipment. Furthermore, this approach would permit existing conventional airborne equipment to obtain service from the new DME/P ground facilities at least during the initial stages of MLS implementation. These compatibility requirements were later incorporated into the DME/P statement of operational requirements which was accepted at an ICAO meeting in April 1981. Further, they have been a primary focus in the DME/P standardization effort which has been actively pursued since late 1980. The conceptual design of the DME/P that evolved from the ICAO process is discussed here. The comptability issues are highlighted, and it is shown how they are accommodated in the system synthesis which also treats the obvious need for a guidance function of high integrity and robust performance in the severe multipath environment encountered in approach and landing operations.

MLS開発の現状と将来

MLS開発の現状と将来

Current Status of the MLS Program

The Microwave Landing System (MLS) is on the verge of implementation in the National Airspace System as a replacement for the Instrument Landing System (ILS). The present plan calls for the establishment of 1,250 systems by the year 2,000. The first ten years of MLS implementation will serve as a transition period in which both ILS and MLS will be extensively used. The MLS implementation strategy is based on the establishment of MLS networks of 4 to 7 facilities. Each network is centered on a major hub airport and the satellites are selected from regional airports that have commuter airline service with the hub. The MLS implementation program will take advantage of the increased reliability of digital electronics systems together with the reduced costs of those systems to provide the capability for all weather service at most MLS-equipped airports.

Routing in the near-terminal area to achieve reductions in airport community noise impact

The introduction of advanced airport terminal-area guidance technology, such as the Microwave Landing System (MLS), will permit aircraft to fly ground tracks through airport communities with significantly greater precision than is possible with current avionics and flight control procedures. It is expected that this improved guidance capability will permit ground tracks to be safely flown which are designed to avoid major population centers in an airport community. This paper will present a general method for defining ground tracks in an airport community which minimize noise impact without violating operational constraints dictated by such factors as air traffic control, aircraft performance, pilot workload, passenger acceptance, etc. A model of airport community noise impact, recently developed at NASA Langley Research Center, has been used to quantitatively assess the reduction in noise impact associated with such flight procedures for a number of airport operating scenarios and airport community population distributions. Results presented in this paper indicate the degree of noise impact reduction which it is practical to expect from noise-minimal aircraft routing in the near terminal area.

Investigation of Control, Display, and Crew-Loading Requirements for Helicopter Instrument Approach

A ground simulation experiment was conducted on a flight simulator for advanced aircraft to investigate the influence and interaction of flight-control system, flight-director display, and crew-loading situation on helicopter flying qualities during terminal-area operations in instrument conditions. Six levels of control complexity were implemented on a representative helicopter model. The six levels of augmentation were examined with display variations consisting of raw elevation and azimuth data only and of raw data plus one-, two-, and three-cue flight directors. Crew-loading situations simulated for the control-display combinations were dual-pilot operation and single-pilot operation. Four pilots performed a total of 150 evaluations of combinations of these parameters for a representative microwave landing system approach task. Pilot rating results indicated the existence of a control display trade-off for ratings of satisfactory, whereas ratings of adequate-but-unsatisfactory depended primarily on the control system; the control system required for ratings of adequate-but-unsatisfactory was clearly more complex for the single-pilot situation than that for the dual-pilot situation.

A 25-W 5-GHz GaAs FET Amplifier for a Microwave Landing System

A 25-W 29-dB gain 5-GHz GaAs FET amplifier has been developed which can be used for a transmitter in the Microwave Landing System. By using 10-W class practical internally matched GaAs FET's hermetically sealed in ceramic packages, the four-stage amplifier has been constructed simply. The amplifier provides 30-W power output with 18.5 percent power efficiency at 17-dBm power input level. It also exhibited an exceffent AM/PM conversion of approximately 1°/dB, compared to 6°/dB for TWT amplifiers.

Improving the MLS Through Enhanced Cockpit Displays

The microwave landing system represents a major advancement in accurate, highly flexible positioning systems permitting the precise definition of curved approach paths. However, the exploitation of these capabilities also requires a comparable advancement in the presentation of information to the pilot. This paper presents a simulator investigation of various prediction and quickening algorithms in computer generated forward-looking displays to improve manual aircraft control on curved MLS approaches. Results indicate that second- and third-order predictor displays provide the best lateral performance. Intermediate levels of prediction and quickening provide best vertical control. Prediction/quickening algorithms of increasing computational order significantly reduce aileron, rudder, and elevator control responses, reflecting successive reductions in cockpit workload. Whereas conventional crosspointer displays are not adequate for manual control during curved landing approaches, perspective displays with predictors and some quickening in the vertical dimension only are highly effective. Additional research is needed to optimize the display for vertical control.

Air Traffic Control Using a Microwave Landing System

Two experiments investigated the performance of air traffic controllers using a simulated Microwave Landing System to control the landing of short takeoff and landing aircraft. In Experiment 1, the task involved the separation of simulated aircraft targets by use of airspeed control. The goal was to ensure that the targets crossed the Missed Approach Point with a specified time interval between them. Experiment 2 employed the same experimental format and task, but the work load was increased by the addition of more targets. Controllers used speed control, radar vectoring, and holding patterns to separate targets. In both experiments, performance was evaluated under no-wind and wind conditions. Significant effects were found due to the configuration of the Microwave Landing System courses and as a result of wind conditions. Performance was generally inaccurate and exhibited high variability. Implications for future development of the Microwave Landing System in the air traffic control system are discussed.

Analysis of Helicopter Operations and the Use of MLS in the Offshore Environment

At the present time the majority of the offshore helicopter operations are in support of the oil/gas industry and most of the offshore heliports are in the Gulf of Mexico. However, the oil companies have started to drill off the Northeast coast, where the weather is much more severe. The severe weather could lead to a need for a precision approach and landing guidance capability on the offshore heliports. The offshore environment is relatively unique; thus, it was decided to determine if the Microwave Landing System (MLS) can satisfy all the requirements for performing precision approach and landing onto an offshore heliport. The study approach includes: the use of a pilot's questionnaire to help determine the requirements; a preliminary analysis of MLS with respect to satisfying the requirements; and a cost-benefit analysis to determine if the life cycle cost of the MLS can be amortized by the potential benefits. As expected, not all the benefits can be quantified and only those benefits easily quantifiable in dollars are compared with the cost of the MLS. The results indicate that MLS has the potential to satisfy the determined requirements but the dollar benefits alone can amortize only a small fraction of the MLS costs, except in rare cases (e.g., very large crew movements). However, a qualitative case for a precision approach capability could be made based on safety benefits and the consequent improvements in crew morale.

Guidance Accuracy Considerations for the Microwave Landing System Precision DME

The microwave landing system (mls), developed by the FAA under a joint DOT/FAA, DOD, and NASA program is designed for extended requirements in volumetric coverage, guidance accuracy, and integrity to meet the increasing needs of aviation. It is to be a common civil-military system and provide a level of operations and equipments suitable for all classes of users. Integral to the Microwave Landing System concept is the Distance Measuring Equipment (DME) which measures range to touchdown. It must satisfy to the maximum extent possible, approach and landing operational requirements for all user aircraft (CTOL, STOL, and VTOL). These requirements dictate aircraft range and range rate measurements with an accuracy at least an order of magnitude more precise than those needed for conventional terminal DME application. This precision DME system (called the PDME) must: (1) satisfy the CTOL Category II decision height and Category III flare maneuver accuracy requirements (100 feet, 2 sigma) when combined with the appropriate elevation data, and (2) for VTOL applications provide accurate range (±40 feet, 2 sigma) and range rate information (±2 knots 2 sigma) to permit IFR decelerated approaches to within 500-foot range of hover. These specifications must be satisfied in the presence of large signal attenuation caused by ground multipath interference and signal time-of-arrival errors induced by lateral multipath (hangars, etc.).

Erratum: New commutated Doppler microwave landing system

Erratum: New commutated Doppler microwave landing system

New commutated Doppler microwave landing system

A new design for a double sideband commutated Doppler system for landing aircraft is proposed. It is capable of providing angular information in elevation and azimuth by the measurement of a Doppler frequency. Furthermore, it offers the possibility of detecting and correcting any multipath error present in the Doppler signal.

Aerospace and military: Space probes score successes; DOD presses high-speed ICs; MLS begins airport tests

Briefly discusses developments including space probes, high-speed integrated circuits, and microwave landing system airport tests.

The Interim Standard Microwave Landing System

Conceived as a bridge between the VHF/UHF ILS and the future international standard Microwave Landing System, ISMLS provides all the operational benefits of conventional ILS with few of the technical headaches. Several ISMLS installations are presently commissioned for public use serving in some cases at sites where site preparation costs for conventional ILS would have exceeded by far the total cost of the rest of the ISMLS installations in commission. These facilities are the world's first public-use microwave landing systems. This paper describes the ISMLS, its signal format, how it copes with difficult siting problems and how it manages to bridge the gap between the existing VHF/UHF system and the future worldwide system, serving the immediate needs of the aviation community.

Aerospace: Landing aircraft under poor conditions: Time-reference scanning beams characterize the all-weather microwave landing system that will replace present systems

Describes the principle of the time-reference scanning-beam microwave landing system (TRSB MLS) which is a system approach to the landing-guidance problem, it can meet a wide variety of diverse-performance, economic, and safety requirements and still supply a universal airborne receiver-processor able to operate with all ground systems. MLS can achieve these objectives because of two major factors: the choice of an operating frequency in the microwave C-band (5 GHz), and the design of its signal format.

System Requirements for Transition From Enroute to Approach Guidance

SUMMARY the airborne system operational/functional requirements (from navigation using enroute aids to navigation using approach guidance) are examined for the transitional phase of an aircraft flight. In this paper the automated navigation system (based nominally on enroute aids) and the ILS/MLS system capabilities are described, and the complementary nature of each is treated. To achieve the full potential benefits of proposed landing system operations, it is suggested that on–board enroute navigation systems will be an important aid to exploit fully the resulting operational capabilities. Proposed microwave landing system capabilities suggest new operational procedures for predefined maneuvers in the terminal area such as close–in captures and complex approach paths. These operational procedures, although only partially available at this time, can be expanded upon based on the operational advantages of the system. Equipment configurations are presented to demonstrate the system requirements.

Guidance Accuracy Consideration for the Microwave Landing System

the microwave landing system (mls) being developed by FAA under a joint DOT/FAA, DOD and NASA program is designed to meet extended requirements in volumetric coverage, guidance accuracy, and integrity to meet the increasing needs of aviation. It is to be a common civil-military system and provide a level of operations and equipments suitable for all classes of users. The current Phase III of the FAA Five-Year Development Program is providing prototype hardware for evaluation and will result in a set of equipment specifications for production equipment. The TRSB has been recommended by an International Civil Aviation Organization (ICAO) technical panel for international standardization. This recommendation will be considered by a meeting of ICAO member states in April 1978. The complete specification of system accuracy is key to the MLS in achieving its operational objectives. There are a number of criteria which this specification must meet. It must provide the guidance accuracy necessary for the intended operations. It must recognize the Flight Control System (FCS) characteristics of the aircraft to be served. It must be expressed in terms which can be measured and also provide design goals for the ground and airborne equipment. The specification must include consideration of the monitor system and the designated alarm limits. This paper presents a proposed accuracy specification for MLS to meet these criteria.