A new miniature color display technology has been developed for airborne helmet-mounted applications. A stack containing three AMLCDs, operating in a subtractive-color mode, is used to obtain 400 X 300 full-color pixels in a 3.3 X 2.5-cm (1.3 X 1.0-inch) active area, yielding a resolution of 118 pixels/cm (300 pixels/inch). Display luminance and contrast are sufficient to produce a 2:1 contrast ratio under worst-case airborne viewing conditions, using typical helmet-mounted display optics. Considerations that led to the selection of this technology for development, results, and future plans are discussed.

The Combat Vehicle Crew Head-Mounted Display (CVC HMD) program is an ARPA-funded, US Army Natick Research, Development, and Engineering Center monitored effort to develop a high resolution, flat panel HMD for the M1 A2 Abrams main battle tank. CVC HMD is part of the ARPA High Definition Systems (HDS) thrust to develop and integrate small (24 micrometers square pels), high resolution (1280 X 1024 X 6-bit grey scale at 60 frame/sec) active matrix electroluminescent (AMEL) and active matrix liquid crystal displays (AMLCD) for head mounted and projection applications. The Honeywell designed CVC HMD is a next generation head-mounted display system that includes advanced flat panel image sources, advanced digital display driver electronics, high speed (> 1 Gbps) digital interconnect electronics, and light weight, high performance optical and mechanical designs. The resulting dramatic improvements in size, weight, power, and cost have already led to program spin offs for both military and commercial applications.

There is a growing requirement for helmet or head mounted display systems that can deliver task-specific information direct to the user on a personal basis. The complexity of this information (and consequently that of the display) can range from simple status indicators through to high quality video. In this paper, we review three miniature display technologies which have been, or are being developed by GEC-Marconi for helmet or head mounted applications. These are light emitting diodes (LEDs), DC thin film electroluminescent displays and ferroelectric liquid crystal over CMOS silicon. The current development status of each of these technologies is reviewed and some of the factors governing the choice of a particular technology discussed.

Active matrix electroluminescent (AMEL) devices are fabricated using circuitry built on the thin-film single crystal silicon on insulator wafers. A 128 X 128 matrix with 24micrometers pixel pitch (1000 lines/inch) is fabricated with higher than 80% fill factor showing initial brightness of above 500fL and high contrast ratios (>100:1). These devices demonstrated the successful combination of active circuitry fabricated using conventional IC processing with standard electroluminescent processing. This AMEL approach provides the potential for head-mounted displays with a very small profile and high efficiency.

We present an overview of diffractive optics technology and the advantages this technology offers when applied to head-mounted displays (HMD). We show especially the impact on weight reduction when diffractive elements are used to correct chromatic aberrations in full-color HMDs. We discuss the effect of higher diffractive orders on image quality and show how to model these effects. Finally, we present the results of a demonstration of a diffractive element in a conventional monochromatic HMD, compare the performance of the hybrid and conventional systems, and demonstrate the validity of our model.

Head mounted displays (HMD) provide one means of displaying virtual environments. This paper assesses the state of HMD technology, with respect to the Virtual Reality (VR) goal of creating an environment which matches user's experience with the real world. We find that current HMDs fall short in important characteristics, such as resolution, field of view, and physical attributes. A system designer, familiar with these limitations, should be able to provide a suitable immersive virtual environment with the inclusion of appropriate graphics rendering techniques and virtual environment input/output devices.

The head tracking systems for helmet mounted displays (HMD) have actually achieved a high degree of accuracy, thus allowing the precise control of the line of sight (LOS) of electrooptical vision sensors. Therefore, the possibility to fly day and night having on the helmet visors the pictures generated by a steerable infrared (IR) sensor slaved to the pilot's head becomes nowadays realistic. The paper describes the results of a technical analysis performed on a system based on a steerable IR sensor integrated with an advanced HMD for navigation aid purpose in a modern fighter. Integration aspects and human engineering factors are also widely analyzed. This paper considers the parameters which lead to an imperfect static or dynamic overlay of the generated IR picture with the external world, as seen by the pilot through the helmet visors, and the effects of such misalignment. The finite angular excursion of the IR sensor LOS, due to the gimbals limits, has been taken into account, and the necessary transitions to and from the LLTVs integrated within the helmet, suitable to cover all possible head motions, have been investigated. An approach for the fusion of information generated by the LLTVs and the IR sensor is also reported. The limits and constraints of navigation using steerable IR sensors are also highlighted with respect to safety aspects.

Since vision is by far the most important sensory input for spatial orientation, it is important to obtain the best visual performance possible from any device. To determine whether current devices were being properly adjusted, visual performance data were obtained from USAF NVG aircrew members after they (1) adjusted the goggle using their usual method of adjustment, (2) used the NVG resolution chart to augment their usual method, and (3) used goggle-adjustment procedures learned in the training class. Results show that without a standard target or procedures, aircrew members were not able to obtain optimal goggle performance - the average visual performance was 20/53 for the 218 aviators in this study. For the 158 aviators who also used the standard target with their usual procedure, there was a significant improvement (average of 20/47). Finally, significantly better goggle performance (average of 20/37) was obtained when 48 aviators adjusted their goggles using procedures learned in the adjustment training class. While these data support the importance of preflight adjustment of NVGs, they represent visual performance under optimal, controlled conditions. It is important to remember that visual performance under actual flight conditions can be significantly impaired with reduced illumination, low contrast levels, improper cockpit lighting, and poor transmissivity of infrared energy through the transparencies.

Visual acuity (resolution) and field of view are two significant parameters used to characterize night vision goggles (NVGs). It is well established that these two parameters are coupled together in an inverse relationship: an increase in field of view results in a reduction in visual acuity and vice versa. An experiment was conducted to determine how visual acuity through NVGs changes as a function of NVG field of view and ambient scene illumination level. A total of three trained observers were used for this study who ranged in age from 33 to 42 years of age. The NVGs used in the study had fields of view of 40, 47, and 52 degrees, respectively. Five levels of ambient scene illumination (corresponding to NVG output luminance levels of 0.01, 0.03, 0.08, 0.26, and 1.9 fL) were provided by a 2856k light source which ranged from overcast starlight to quarter moon. The targets used in the study were approximately 95+% contrast square wave targets ranging in size from 45 cycles/degree to 5 cycles per degree. The method of adjustment was employed by having the trained observer start at a distance of 30 feet and determine the highest spatial frequency target which was clearly discernable. The subject was then directed to walk back slowly from the target until it was just out of focus, and then walk forward until the target was barely discernable. The distance from the target was recorded and used to calculate the angular spatial frequency (and equivalent Snellen acuity). The results indicate that the simple geometric model of the inverse relationship between resolution and field of view is adequate for characterizing this design trade-off for the quality of image intensifier tubes currently available.

Because of limitations in the size of the field-of-view (FOV) available in helmet mounted displays (HMD) using the full overlap display mode, where the entire FOV is binocular, partial binocular overlap displays, which can be convergent or divergent, have been proposed. One consequence of this is a perceptual effect known as luning, which is a subjective darkening in the monocular regions of the FOV, which can in some cases cause fragmentation of the FOV into three regions. A concern is the possible effect on target identification in the monocular regions, particularly in areas affected by luning. We review data we have collected in our binocular vision lab on the effect of display mode on these aspects of visual perception.

The focusing response of the eye (accommodation) is degraded in monochromatic light for many subjects. To find out whether this degradation also occurs in narrowband polychromatic light, we measured the accommodation of nine young adult volunteer subjects across three bandwidths (10, 20, and 80 nm) and a broadband control (white light). The peak wavelength was 550 nm for each of the bandpass filtered stimuli, and the luminance of all targets was 10 cd/m². Accommodation was measured with a dynamic infrared optometer while the subjects viewed threshold size, high-contrast letters under both dynamic and steady-state conditions. In the former, the optical distance of the target was varied sinusoidally from 0.0 to 2.0 diopters (optical infinity to 50 cm) at a temporal frequency of 0.5 Hz, while in the latter it was held constant at 1.0 diopter (1.0 m). We found that, under dynamic conditions, accommodative accuracy steadily improved in a statistically significant way with increases in spectral bandwidth. Under steady-state conditions, there was no statistically significant trend. These results suggest that accommodation might suffer from the use of narrowband phosphors in helmet-mounted displays under dynamic conditions, i.e., the observer might accommodate inaccurately to the display if frequent changes in focus to and from the display are required.

The current practice of basing the performance of cathode ray tube (CRT) displays solely on static image quality figures-of- merit fails to provide a valid assessment of a display's ability to reproduce real-world scenes where there is relative motion within the scene or between the sensor and scene. Techniques which provide assessment of a display's capability to reproduce spatial information in a dynamic environment are needed. One technique based on response to sinusoidal counterphase modulation is presented.

The requirements for head-mounted displays (HMDs) continue to become more demanding. Increased light throughput, reduced weight and higher optical performance mandates the use of new optical technologies. Diffractive optical elements can provide the optical designer additional degrees of freedom to develop more sophisticated lightweight color HMD systems. A method of design is discussed along with several manufacturing methods for producing diffractive elements including single-point diamond turning and laser pattern generation. Due to the unique characteristics of diffractive elements regarding efficiency and diffraction orders, it is vitally important to properly characterize and test these systems. The efficiency of a diffractive element can have a profound impact on the performance of the optical system; therefore, it is necessary to accurately measure the diffraction efficiency and correctly interpret the impact on the MTF. An example of a hybrid diffractive/refractive relay lens is presented to demonstrate the relationship between the MTF and diffraction efficiency.

The way in which a pilot's attention is distributed between various operational tasks during tactical flight is of prime importance when designing new cockpit displays. The point of regard, and by inference, the pilot's focus of attention, can be determined by measuring head and eye position. The measurement of head position using an electromagnetic coil technique is well proven in flight. However, most techniques currently available for determining eye position are too bulky and complex, compromise ejection safety and cannot, as yet, be used in the fast jet cockpit. This paper reports a feasibility study into the use of the electro-oculogram (EOG) to determine eye position during flight in a fast jet aircraft. EOG amplifiers have been designed for airborne use and three flight trials have been conducted in a Jaguar combat aircraft. Laboratory calibration studies have shown good linearity of the horizontal EOG, but some nonlinearity of the vertical EOG which is better described using a second order polynomial. In addition, there is an interaction between the horizonal and vertical components. These studies indicated that for an individual subject, an adequate calibration in both the horizontal and vertical planes could be achieved with a minimum of nine calibration points, but that the accuracy of the measurement was limited by the drift of the EOG signal. Results of the flight trials to validate this method will be presented.

An electromagnetic tracking system is evaluated as a series of reference coordinates systems, where rotation operators transform one reference frame to the next. System errors are identified. Methods for system boresighting, EM field deviation mapping and accuracy testing are presented. Error correction of the mapped field deviation is discussed.

We show an optoelectronic implementation assistant that will be used by handicapped people. The system works with the head gesture movements of the user. These movements are vectorized with an IR spotlight that is detected by four optocoupled detectors. The information is interpreted and sent to the PC by the serial port. This implementation could be used as a powerful tool between man-machine interaction.

Agile aircraft (X-29, X-31, F-18 High Alpha Research Vehicle and F-16 Multi-Axis Thrust Vector) test pilots, while flying at high angles of attack, experience difficulty predicting their flight path trajectory. To compensate for the loss of this critical element of situational awareness, the X-31 International Test Organization (ITO) installed and evaluated a helmet mounted display (HMD) system into an X-31 aircraft and simulator. Also investigated for incorporation within the HMD system and flight evaluation was another candidate technology for improving situational awareness -three dimensional audio. This was the first flight test evaluating the coupling of visual and audio cueing for aircrew aiding. The focus of the endeavor, which implemented two visual and audio formats, was to examine the extent visual and audio orientation cueing enhanced situational awareness and improved pilot performance during tactical flying. This paper provides an overview of the X-31 HMVAD system, describes the visual and audio symbology, presents a summary of the pilots' subjective evaluation of the system following its use in simulation and flight test, and outlines the future plans for the X-31 HMVAD system.

NASA and the U.S. Army have designed, developed and flight evaluated a Computer Aiding for Low-Altitude Helicopter Flight (CALAHF) guidance system. This system provides guidance to the pilot for near-terrain covert helicopter operations. The system automates the processing of precision navigation information, helicopter mission requirements and terrain flight guidance. This automation is presented to the pilot through symbology on a helmet mounted display. The symbology is a 'pilot-centered' design which preserves pilot flexibility and authority over the CALAHF system's automation. An extensive flight evaluation of the system has been conducted using the U.S. Army's NUH-60 STAR (Systems Testbed for Avionics Research) research helicopter. The evaluations were flown over a multi-waypoint helicopter mission in rugged mountainous terrain. The system was evaluated at terrain clearance altitudes from 300 to 125 feet, and airspeeds from 40 to 110 knots. The results of these evaluations showed that the pilots could precisely follow the automation symbology while maintaining a high degree of situational awareness.

Future air battles will increasingly rely on aircraft capable of directing their advanced weapons with greater accuracy and at larger off-boresight angles. Analysis of current threats indicate that potential adversaries include this enhanced technology in their aircraft today. Helmet-mounted Tracker/Displays (HMT/D) provide a ready and capable response to that threat. These pilot- friendly systems allow the pilot to lock-on to targets and fire missiles at much greater angles than normally allowed in the head up display (HUD). Vista Sabre II is a congressionally mandated special project to evaluate a helmet-mounted display in an operational environment. The program effort involves the installation of two helmet-mounted tracker/display systems on two operational F-15C aircraft for demonstrating the capabilities of this technology in air-to-air combat. The system will provide the pilot with weapon status, targeting information, and other important, time critical, information necessary for effective air-to-air engagements at any head orientation without having to look into the cockpit or through the head up display (HUD). Also integrated into the system is a Navy high off-boresight missile seeker (HOBS) with extended range capability to track targets at high angles off the aircraft's boresight. The helmet display and HOBS will help the pilot lock a missile faster and simulate the missile launch. During the period of demonstration flights, the system will be evaluated through all aspects of the close-in, visual air-to-air combat arena, as well as investigating the human factors issues unique to helmet-mounted systems.

The Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) is a UH-60A Black Hawk helicopter that is being modified by the US Army and NASA for flight systems research. One of the objectives of the research is to develop and integrate technologies for Automated Nap-of-the Earth (ANOE) flight. The principal elements of this system include video imaging sensors, advanced real-time image processing capabilities, a graphics supercomputer, a wide field-of-view color helmet mounted display (HMD), and an advanced fly-by-wire flight control system. The development methodology and the current status of the ANOE Flight Program are summarized, a description of the visionics system is provided, and the plans for the initial applications of the color HMD are presented.

Naval Air Systems Command (AIR5117D) tasked the Flight Test Engineering Group (FTEG) of the Naval Air Warfare Center Aircraft Division (NAWCAD) to conduct a technical analysis of the 'blue' night vision device (NVD) lighting kit as installed on the KC-130 aircraft. As a part of this analysis FTEG was additionally tasked to provide a 'quick look' evaluation of a manufacturer installed, ANVIS compatible, head up display (HUD). The HUD was provided by Elbit Corp. of Israel.

Many parallels exist in the current development of helmet-mounted displays (HMDs) to what has transpired for the head-up display (HUD). This paper reviews HUD flight testing results for similarities to the symbology and display format requirements for HMDs. Analogies are drawn to HMD development from these lessons learned. Design guidance and pilot-in-the-loop test and evaluation techniques are proposed.

The helmet-mounted display (HMD) presents flight, navigation, and weapon information in the pilot's line of sight. The HMD was developed to allow the pilot to retain aircraft and weapon information while looking off boresight. The present study reviewed the state-of-the-art in HMDs and identified a number of issues applying to HMDs. Several are identical to head-up display (HUD) issues: symbol standardization, excessive clutter, and the need for integration with other cockpit displays and controls. Other issues are unique to the head-mounted display: symbol stabilization, inadequate definitions, undefined symbol drive laws, helmet considerations, and field-of-view (FOV) vs. resolution tradeoff requirements. Symbol stabilization is critical. In the Apache helicopter, the lack of compensation for pilot head motion creates excessive workload during hovering and nap-of-the-earth (NOE) flight. This high workload translates into excessive training requirements. At the same time, misleading symbology makes interpretation of the height of obstructions impossible. The underlying cause is the absence of design criteria for HMDs. The existing military standard does not reflect the current state of technology. In addition, there are inadequate test and evaluation guidelines. The situation parallels the situation for HUDs several years ago.

This paper is based upon an effort in support of the Armstrong Laboratory, Helmet Mounted Sensory Technology Advanced Development Program (HMST ADP). That effort produced a report which provided the HMST ADP with information to make informed helmet system development decisions. These would be based upon not only crew, but aircraft and mission requirements. Specifically addressed were the following items (portions of them are discussed within this paper): the background of Helmet Display (HD) research and USAF decisions, current aircraft capabilities that support HDs, HD types, aircraft and HD utility, integration with current and future avionics and weapon systems and some analytical conclusions. This work was to project the potential elements which make up those decisions, such as crew, weapons, sensors, aircraft and missions into four HD option descriptions as representative of the technology for examination. These four are discussed throughout this paper as: austere, semi- austere, helmet-mounted head-up display (HUD) and helmet-mounted display (HMD).

To employ the most readily comprehensible presentation methods and symbology with helmet-mounted displays (HMDs), it is critical to identify the information elements needed to perform each pilot function and to analytically determine the attributes of these elements. The extensive analyses of mission requirements currently performed for pilot-vehicle interface design can be aided and improved by the new capabilities of intelligent systems and relational databases. An intelligent system, named ACIDTEST, has been developed specifically for organizing and applying rules to identify the best display modalities, locations, and formats. The primary objectives of the ACIDTEST system are to provide rapid accessibility to pertinent display research data, to integrate guidelines from many disciplines and identify conflicts among these guidelines, to force a consistent display approach among the design team members, and to serve as an 'audit trail' of design decisions and justifications. A powerful relational database called TAWL ORDIR has been developed to document information requirements and attributes for use by ACIDTEST as well as to greatly augment the applicability of mission analysis data. TAWL ORDIR can be used to rapidly reorganize mission analysis data components for study, perform commonality analyses for groups of tasks, determine the information content requirement for tailored display modes, and identify symbology integration opportunities.

In spite of advances in technology, spatial disorientation (SD) continues to be a contributing factor in a large proportion of military aircraft accidents. Data from published reports of SD, and aircraft accident folders over the past three and one-half decades, were analyzed. The rate of major aircraft accidents per 100,000 flying hours decreased from 5.36 during the 14-year period of 1958-1971 to a rate of 2.22 during the 21-year period 1972-1992. During the same two time periods, however, the rate of SD caused major aircraft accidents per 100,000 flight hours remained approximately constant (0.32 and 0.35, respectively). Even though the average number of SD mishaps decreased from 23 per year in the 1958-1971 period to 12 per year in the 1972- 1992 period, the percent of SD accidents increased from an average of 6% during 1958-1971 to an average of 16% in 1972-1992. SD accidents still represent a major drain on USAF resources; but the development of helmet- mounted display technology provides an opportunity to present SD in some of the more demanding operational environments.

This paper documents an inexpensive apparatus intended for rapid prototyping and evaluation of alphanumeric and symbolic display formats. Emphasis is placed on symbology design for use in wide field of view (FOV) helmet-mounted displays (HMDs). The apparatus consists of a Silicon Graphics, Inc. (SGI) computer with standard monitor and mouse, Virtual Applications Prototyping System (VAPS) software, a rapidly reconfigurable flight simulator program (FLSIM), and a Fresnel lens-based optical system affording an 85 degree(s) X 70 degree(s) field of view. A preliminary experiment was conducted to verify the suitability of the apparatus for objective measurement of pilot performance during flight simulation. Five test participants attempted to maintain specified altitude and airspeed parameters while maneuvering an aircraft around a simulated airfield. Necessary flight information was presented via symbols located to the left and right of display centerline. Lateral separation between these symbols was varied; values of total angular separation ranged from 30 degree(s) to 70 degree(s), in 10 degree(s) increments. Test results indicate that the apparatus is suitable for the purpose intended. It was also determined that pilot performance in a demanding flight task may not necessarily degrade with increasing lateral separation when a wide field of view format is employed. This surprising (though preliminary) finding suggests that further research is warranted. Recommendations are made to further refine the apparatus and experimental methodology.

Abstract not available.

To enhance manned extravehicular activity (EVA) utilizing an extravehicular mobility unit (EMU)(i.e., a space suit and portable life support backpack), NASA has conducted research into implementing helmet mounted display (HMD) and related technology within its next generation of space suits. The NASA/Johnson Space Center has completed four feasibility development programs for the design and development of an EMU HMD, each resulting in the delivery of a binocular or biocular HMD breadboard unit utilizing conventional optical elements (i.e., glass lenses and beamsplitters) and/or holographic optics. Additional research into combining the use of voice recognition for astronaut 'hands- free' access to information via the HMD has also been conducted. Research conducted since 1983 will be summarized along with current shuttle EMU display enhancements. In addition, recommendations for the design of the next generation of displays for use within the EMU will be presented.

The U. S. Army Aeroflightdynamics Directorate's (AFDD) Crew Station Research and Development Branch (CSRDB) conducted a multiphase effort to develop symbology displaying information from the Obstacle Avoidance System (OASYS) on the Aviator's Night Vision System (ANVIS) Head Up Display (HUD). The first phase of this program used static symbology displayed on a workstation to identify the types of information required from OASYS by the pilot. The second phase used a low-fidelity, pilot-in-the-loop simulation to evaluate fourteen different symbology-drive law combinations. Based on the results of phases 1 and 2 three candidate symbologies were selected, along with the baseline symbology developed by the OASYS contractor, for evaluation in full mission simulation. In addition, a full-daylight, full field-of-view condition and Night Vision Goggle (NVG) condition, both without OASYS symbology, were used as control conditions. The environmental conditions (e.g., ambient illumination, visual range) and task requirements (e.g., altitude and airspeed) used in the simulation were selected to severely tax the symbology. Reliable differences in performance between symbology conditions were found. Two of the symbologies developed during the earlier phases of this program resulted in reduced frequencies of ground strikes compared to OASYS baseline and NVG only conditions. The frequency of close approaches to wires was lower with the symbology developed in this program than with the baseline symbology. All OASYS symbologies improved performance relative to the NVG control condition. It is recommended that the OASYS symbology and drive laws developed during this program be used during OASYS flight tests.

Combat mission scenarios require pilots to maneuver their aircraft over and around various terrain features at high speeds and low altitudes day, night, or in adverse meteorological conditions. While current systems (e.g., Night Vision Goggles and FLIR) provide some support for the pilot, they are not adequate in many weather conditions. However, the effects of adverse weather can be overcome using the U. S. Defense Mapping Agency's digital terrain elevation database to create a synthetic terrain image (STI). The concept of synthetically derived terrain imagery, projected as background on a Helmet-Mounted Display, was investigated in regards to its utility for enhancing pilot terrain awareness. An initial study using four Lockheed pilots and six USAF pilots was conducted to determine subjective preference of STI formats. A follow-on study, using two preferred formats, evaluated STI in a full-mission simulation environment. Six F-16 pilots completed a half day of training and a one day evaluation. Data was collected on missions involving low level navigation, followed by a laser guided bomb loft or offset roll- in dive bomb attack. Thirteen missions per pilot were completed including bomb runs using LANTIRN without STI. All the runs were at night with either 'poor' or 'good' FLIR conditions over rough or moderately rolling terrain. The evaluation indicated that pilots found STI to be useful and offered real-time support for low level navigation. Some problems still exist (e.g., field of view of HMD), which will be investigated in future studies.

Symbology night vision goggles (SNVGs) which can be worn by fast- jet aircrew have been developed and tested. The goggles are designed to be linked with a head tracker system and provide weapon aiming symbology with line-of-sight cueing, significantly enhancing both air to air and air to ground night operations. The SNVGs are compatible with NVG auto-separation systems. Flight trials have been conducted with favorable results. This work was sponsored under UK MOD Research Packages.

This experiment compares the utility of three off-boresight helmet-mounted display (HMD) symbology information levels for high angle target search and intercept during a simulated air-to-air engagement. The information levels included: Head-Up Display (HUD) presentation of both ownship status and target location, HUD status plus HMD target location, and HUD status plus HMD target location plus HMD ownship status. Four different attitude symbology elements were evaluated within ownship status level. The levels of the information condition variable evolved from the following questions: 1) Will HMD ownship status information help the pilot fly while searching for threats? 2) Will HMD target location information help the pilot find, intercept, and track an airborne target? 3) What is the effect of combining aircraft status and target location information within the HMD? 4) If ownship status information is helpful, are there symbology features which are more interpretable than others? The objective of this research was to determine of ownship status information within the helmet display symbology (HDS) set is necessary in an air-to-air application. The findings suggest that HDS will be advantageous, but task dependent. A strong subjective preference for including ownship status information within the HDS was found.

Aircraft instrumentation presentations are based on the recognition of static patterns. Evidence is produced to show that the visual system can respond to velocity input alone and that when it does so this constitutes an independent channel of information which does not conflict with foveal processing and that this response extends out to the limits of the periphery of vision. The experimental work described tests the ability of this aspect of vision to reduce clutter and obscuration in screen projected instrument displays. Experienced aircrew subjects are required to carry out a simulated low level lob-bomb attack followed by the rapid acquisition of an escape vector while simultaneously tracking the target presented in a space stabilized view. There are four experimental conditions, the tracking task being common to all four. Two conditions use the standard RAF fast jet head-up flight control display and two use a velocity based display which is presented in the annulus between 20 and 40 degrees visual angle. This display does not require foveal attention so the central area can be left clear. Each display is tested in two conditions. In one the tasks are presented side by side forcing subjects to switch gaze between the two. In the other the two are combined. With the peripheral display the tracking task occupies the clear central area but with the NATO version it has to share this with the flight information.

Helmet-mounted display (HMD) symbology for an automated Nap-of-the-Earth (NOE) guidance and control system is described. In the automated system, referred to as Pilot-Directed Guidance (PDG), pilot control inputs are interpreted as high-level velocity commands to an inner-loop guidance and control system that is responsible for obstacle detection and avoidance maneuvering. The success of the PDG concept has been shown to be highly dependent upon the intelligent use of inertially stabilized symbology to provide navigational information and velocity command feedback to the pilot. Individual symbol functions and drive laws are described along with the associated display difficulties encountered at NOE airspeeds and altitudes. The important findings of a fixed base simulation experiment, relating to the use of HMD symbology, are given along with pilot commentary and opinion.

Thirty-two pilot subjects flew instrument approaches in a visually high-fidelity simulator. Location of flight symbology was manipulated while controlling for optical distance and symbology format. Subjects were assigned to one of two symbology sets, conformal or non-conformal. Each subject flew half of the trials with the symbology presented in a head-up location and half with the symbology located head-down. An unexpected far domain event was presented on one trial per subject. The results revealed that, for flight path control, there was generally a cost associated with head-down location. The magnitude of this cost was relatively larger for conformal than for non-conformal symbology. Head-up presentation resulted in faster transition from instrument to visual flight references, but slower response to the far domain unexpected event.

The mission of the Helmet-Mounted Systems Technology (HMST) Advanced Development Program Office (ADPO) is to demonstrate advanced helmet systems to the using community. Months, sometimes years, of coordination with engineers, logisticians, air framers, safety personnel, pilots, and others, pass by before the first day of system integration into the aircraft can begin. One such integration and demonstration occurred during January and February 1993. With HMST acting as the Integration Engineer, the Air Force Special Mission Operational Test and Evaluation Center (SMOTEC) conducted an Operational Feasibility Test and Evaluation (OFT&E) of a Helmet-Mounted Tracker and Display (HMT/D) system on a MH-53J PAVE LOW. The addition of the helmet display, helmet tracker, and wider field-of-view of the Forward-Looking InfraRed (FLIR) sensor were only a few of the integration issues that had to be resolved prior to the first flight. This paper will focus on the coordination, integration, demonstration, and evaluation of the HMT/D in the PAVE LOW.

Helmet mounted displays have a significant role to play in a number of military airborne applications. Many concepts have been built and tested over the past 20 years, but very few have been adopted for extensive use in the demanding environment found in typical military aircraft cockpits. Of the many types of display configurations tried, display projection off the visor is, from the users point of view, the preferred method of presentation and several development products of this type are now available. GEC-Marconi Avionics 'VIPER' is an approach to this particular helmet mounted display configuration, and was conceived with the objective of using well proven techniques, technologies and where possible standard flight equipment. This paper discusses the design approach, trade offs and initial flight trials experience with the Viper Helmet Mounted Display.