avionics displays · 2017-08-25 · the display technology options are then discussed along with...

Avionics Displays

Kalluri R. Sarma*, Steve Grothe and Aaron GannonCrew Interface Technologies, Honeywell International, Aerospace Advanced Technology, Phoenix, AZ, USA

Abstract

Avionics flight deck displays are a critical part of the aircraft avionics system. They are designed to serve auseful purpose for the crew, referred to as “intended function” by certification regulations. Regulationsrequire flight deck equipment to be usable in both control and display aspects and to be designed tominimize human error. Historical evolution of the flight deck displays is discussed, followed by adiscussion of current avionics display applications with enhanced features and functions. The opticalimage quality and operational environmental performance requirements as they relate to intendedfunctions are then discussed. The display technology options are then discussed along with the uniqueaspects of adapting them for the flight deck use. While AMLCD is the current display technology ofchoice, it has evolved greatly since it was first adapted for the flight deck use for the first time about20 years ago. Various types of AMLCDs and their design considerations for avionics applications are thendiscussed, along with touch screen interfaces and human factors. Potential of projection displays and theemerging AMOLED technology and flexible displays for future flight deck use is also discussed.

Introduction

The commercialization and the continued technology advances in active-matrix displays in recent times,particularly during the past two decades, have been and continue to be phenomenal. While it is wellknown how these new types of displays, particularly active-matrix liquid-crystal displays (AMLCDs),have enabled mobile electronic (computer and communication) devices such as notebook PCs, high-resolution smartphones, and other consumer electronic items such as large screen TVs, their impact onother areas such as avionics flight decks has been equally impressive. This chapter discusses displays foravionics flight decks. Avionics flight decks range from military and commercial aircraft to space vehiclessuch as the Space Shuttle and International Space Station (ISS). Further, commercial aircraft flight decksrange from large air transport aircraft such as B777 and A380, to business jets such as G650, to generalaviation aircraft and helicopters. Military flight decks can be for transport, strategic (e.g., bomber), andtactical (e.g., fighter) aircraft and military helicopters.

The earliest powered aircraft did not have flight deck displays, but relied only on the pilot’s own directsensation and perception as provided by rudimentary instruments for aircraft control and performance.For instance, related to the aviate task, airspeed was a proxy for angle of attack, so the pilot could knowhow well the wing was flying, pressure altitude was substituted for height over the earth, and a horizonline indicated orientation. Navigation used such tools as the clock or stopwatch and the magneticcompass. As aircraft complexity, speed, and altitude quickly outstripped the human’s sensory capabilities,it was evident that some additional display instrumentation was needed. Both the aviation technology andthe integration of displays in flight deck displays have advanced tremendously during the last 100 years.Instruments today can provide insight into thousands of parameters inside and outside the aircraft with

*Email: [email protected]

Handbook of Visual Display TechnologyDOI 10.1007/978-3-642-35947-7_168-1# Springer-Verlag Berlin Heidelberg 2015

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great precision, because displays have advanced from stand-alone, dedicated mechanical or electrome-chanical units to large format displays run by a graphics processor.

The emergence of electronic displays and their application to aircraft flight decks has had a profoundimpact on the functional, safety, and life cycle economics aspects of aircraft operations. Evolving sincetheir first applications, electronic display indicator systems have progressively displaced the myriad ofelectromechanical instruments that had been dedicated to single, or limited, functions. Advanced func-tionality, such as moving map displays, has been enabled by electronic displays and has providedbreakthrough improvements in offering pilots better situational awareness, systems management, andoperational flexibility. In today’s flight decks, even real-time synthetic representations of the outsideenvironment can be displayed on these new types of displays, dramatically enhancing the pilot’sawareness of the aircraft’s progression through the flight, even in very limited visibility conditions.

With the increasing reliance on electronic displays in the flight deck, attendant safety considerationsmust be addressed. The availability and integrity of the information presented must satisfy the operationaland safety needs of the aircraft. Careful attention to readability, redundancy, monitoring, hardware andsoftware design assurance measures, and backup systems play crucial roles in ensuring that the displaysystem will adequately support these needs.

As with any aircraft system, life cycle economic benefits must be achieved. With larger, fewer, andmore common part number displays being used, cost advantages quickly emerge in reduced design effort,spares requirements, and growth capability (e.g., through software upgrades). Electronic displays alsohave facilitated higher levels of automation in other aircraft systems, leading to operational cost advan-tages such as reducing the number of flight deck crew members needed to safely operate the aircraft.

Electronic displays in flight deck applications evolved with, and often became drivers for, theadvancement of the state-of-the-art for displays. Small, monochrome, limited function CRTs eventuallygave way to highly functionally integrated, large format LCDs that satisfy the unprecedented challengesfor display usability in the modern flight deck environment (e.g., lighting, EMI, vibration, temperature,human factors).

Current avionics flight decks use head-down displays (HDD) as well as head-up displays (HUD) andnear to eye (NTE) or head-mounted displays (HMD). This chapter focuses on the HDD applications.

Historical Evolution of Avionics Displays

Early applications of flight deck electronic displays were for military aircraft and were of relatively smalldisplay area, CRT-based, often monochrome, and limited in functionality to text or simple graphics. Toachieve readability requirements for the high ambient light conditions of the flight deck, high luminance(e.g., stroke, or “calligraphic”) and antireflectance strategies were employed. It was also important for thedisplays to be compatible with night operations, requiring sufficient dimming range to ensure that thepilot’s night-adapted vision, as well as when using night vision imaging systems (NVIS), is not affected.

Ruggedized shadow mask CRT displays added full color capability, dramatically enhancing usabilityand enabling more functional integration on increasingly larger area displays. Challenges includedconvergence, precise color tracking over a very wide dimming range, and achieving required readabilityin the flight deck environment. Shadow mask flight deck displays typically incorporated hybrid (i.e.,raster and stroke) technologies in order to achieve the readability and other functional requirements.

LCD technology has enabled dramatic improvements in size, weight, and power, along with thecapability for enhanced display presentations. Significant challenges, however, needed to be overcometo develop avionics-grade LCDs that meet the operational requirements for use in the flight deck. EarlyLCDs suffered from narrow viewing angles, sluggish performance in low temperatures, “clearing” at


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relatively lower temperatures thereby limiting high-temperature performance, poor color tracking withgrayscale, and low luminance. All these items needed to be addressed by the avionics industry for theflight deck use, and several innovations in LCD technologies were driven for this very challengingapplication. Early flight deck LCDs were highly customized and pushed the state of the art. Figure 1shows examples of these early flight decks utilizing AMLCDs. Eventually, many of the high-performancecharacteristics first required for flight deck applications became broadly available across many, includingconsumer, display markets. Increasingly larger LCDs have improved their functional integration capa-bilities and have resulted in fewer displays being necessary for a flight deck.

Along with advances in the display media, increasingly powerful processors and graphics renderingengines have provided capability to present display formats that are highly integrated, visually intuitive,and aesthetically pleasing. The pilots can be presented with important information when they need it andin a more natural way that reduces the amount of interpretation necessary in order to mentally “visualize”the state and orientation of the aircraft. As electronic displays also lend themselves to flexible controlssuch as cursor control devices and touch screens, the potential for reducing the number of dedicatedcontrols in the flight deck while further facilitating functional additions and upgrades is being realized.

Avionics Display Applications

This section discusses the role of displays in the cockpit as they relate to the operational aspects of theaircraft application. The aircraft operational requirements dictate the display performance requirementsand thereby its design.

Fig. 1 Examples of early flight decks using AMLCD avionics displays. (a) B777, (b) G550, and (c) Space Shuttle


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Display Utility and UsabilityFlight deck displays are designed to serve a useful purpose for the crew. Certification regulations refer tothis useful purpose as an intended function and generally require flight deck equipment to be designed toaccomplish its intended function with a level of assurance. More recent regulations require flight deckequipment to be usable in both control and display aspects and designed to minimize human error (FederalAviation 2002). Accordingly, flight deck displays can be characterized at a high level in terms of theirutility, i.e., the useful purpose or intended function they provide, and their usability, with respect to theease with which they provide this useful function to the crew.

Displays and Crew FunctionsDisplay utility is tied to the crew functions and tasks it serves, which are in turn guided by operationalgoals such as safety, mission effectiveness, efficiency, and passenger comfort. To accomplish these goals,the core functions that crews execute are:

1. Aviate2. Navigate3. Communicate4. Manage systems

The priority of crew functions and tasks generally favors this hierarchy, such that the aviate function isthe most critical and handled first. During normal and non-normal flight deck events, functions maychange priority, and in practice, crews continuously transition, share, and balance functions and tasks,using other people and aircraft systems and automation to accomplish their tasks.

Aviate tasks relate to managing power and airspeed appropriate to the phase of flight and configuration,as well as coordinating pitch, roll, and yaw to maintain straight and level, turning, and climbing anddescending flight. Aviate tasks are generally associated with a very short or tactical time frame, unfoldingover seconds or minutes, and involving monitoring, control, and repetition over this time frame. Displaysused within the aviate task are often grouped today onto a primary flight display (PFD) or head-up display(HUD) and include primarily, but are not limited to:

• Airspeed indicator• Altimeter• Attitude indicator• Standby instrument• Heading indicator• Flight mode annunciator

While most of these displays can be clearly tied to the aviate task, the idea of blending or transitioningtasks is evident with the heading indicator (which may be used with navigate tasks) or the flight modeannunciator, which may be used in a supervisory fashion with the manage systems task. Figure 2 shows anexample of a PFD.

Navigate tasks generally involve more strategic ends, and the purpose of the flight itself is oftenreflected in these navigate tasks such as “travel most efficiently from point A to point B, adhering to aplanned route over a series of waypoints, to arrive safely at the destination at a particular time.” Whileaviate tasks may happen second to second or minute to minute, navigate tasks generally unfold on a longertime frame, minute to minute or hour to hour, although some monitoring and control tasks can occur onshorter time frames and may become blended with aviate tasks. Navigate tasks also address the challenges


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in efficiently reaching the destination, such as weather or traffic that may require delay, deviation, ordiversion from the planned route. Flight deck navigate displays include:

• Horizontal situation indicator (HSI) (course and deviation bars)• Lateral map and information layers (e.g., airspace, terrain, traffic, weather)• Vertical situation display (VSD)• Waypoint list, graphical flight path depiction• Flight management systems (FMS) functions (e.g., legs, progress, and/or route pages)

Some displays may cross between aviate and navigate functions, depending on the time frame andurgency. In particular, displays of weather, terrain, and traffic may be first used strategically for planningand long-term avoidance but may be used tactically for aircraft maneuvering, as a threat emerges. Figure 3shows an example of a NAV display.

Communicate tasks reflect the command and coordination of flight goals within the cockpit and withground air traffic facilities. While their own separate category, communicate tasks nearly always facilitateor accomplish some other flight deck functions or tasks. For instance, when an air traffic controller issues aclearance, this clearance manifests as a communicate task, but almost always results in a change to thenavigate or aviate task. Communicate tasks involve authority, such as that of the controller in issuing aclearance, but can also include simple sharing of information to raise shared situational awareness, such asa captain pointing to a map feature and describing an associated, upcoming plan. Communicate tasks mayappear to happen as ad hoc events, but observing across several flights reveals the predictability andpatterns that communicate tasks embody when associated with phases of flight such as taxi, takeoff,approach, and landing. In addition to all the displays that may be used to facilitate intra-crew coordination,

Heading IndicatorHorizontal Situation Indicator

AirspeedIndicator

Altimeter

AttitudeIndicator

Flight ModeAnnunciators

Fig. 2 Illustration of a primary flight display (PFD)


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dedicated displays associated with communicate tasks include communication radios and data linkcommunications.

Manage systems tasks are generally associated with the internal operations and health of the aircraft. Innormal conditions, checklists are used with the displays to set up the desired system states according tophases of flight (e.g., engine start, taxi, takeoff, climb, etc.). In non-normal conditions, displays alert thecrew to failure states, give insight into associated systems, and provide emergency management throughnon-normal checklists. Checklists associated with engines and systems displayed on flight deck displaysto facilitate the manage systems task include:

• Primary and secondary engines• Crew alerting system• Configuration displays (e.g., flaps/slats, spoilers, trim, gear)• System synoptics, such as fuel, pressurization, electrical• Normal and non-normal electronic checklists

Thus, the flight deck displays working in conjunction with other avionics systems enhance situationalawareness and flight safety under the entire range of flight and ground conditions including bad weather,low visibility, turbulence, and high-density traffic. Additional examples of intended functions include anenhanced ground proximity warning system (EGPWS) display utilizing synthetic vision, terrain data-bases, and innovative symbology that alert pilots if their aircraft is in immediate danger of flying into theground or an obstacle. Combined vision systems (CVS) displays that use an overlay of IR sensor (or othersensors) data with an out-the-window view significantly increase the ability to land at many airports. Withthe CVS display in the cockpit, pilots are allowed access to many airports in low-visibility conditionswhich would otherwise have been beyond their reach under the FAA (Federal Aviation Administration)regulations.

Lateral Map & Information Layers

Vertical Situation Display

WaypointList

Graphical Flight Path

Flight Management System Functions

Fig. 3 Illustration of a NAV display


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Performance Requirements of Avionics Displays

Compared to displays used in consumer applications, avionics displays have some unique optical andenvironmental performance requirements due to their unique operational environments.

Optical Image Quality Performance RequirementsOptical performance requirements are numerous. Example operational performance requirements forcommercial aircraft can be found in the ARP (aerospace recommended practice) documents such as SAEARP4256: Design Objectives for Liquid Crystal Displays for Part 25 (transport) Aircraft and SAEARP4260: Photometric and Colorimetric Measurement Procedures for Airborne Flat Panel Displays.The minimum performance requirements for FAA certification of electronic displays are given inTSO-C113a which refers to SAEAS-8034B:Minimum Performance Standard for AirborneMultipurposeElectronic Displays. Important optical performance parameters include:

• Luminance• Chromaticity• Dimming range• Sunlight readability• Contrast ratio (under dark and bright ambient conditions)• Reflectance• Field of view (FOV)

– Contrast ratio– Gray-level luminance uniformity– Chromaticity uniformity

• Response time• Long-term image retention (LTIR)• NVIS performance

The luminance requirement for avionics displays is much higher (~350–850 Cd/m2) than that forAMLCDs designed for consumer applications (~100–300 Cd/m2). Consumer displays usually use light-collecting backlight films that reduce the luminance off the normal axis to increase the luminance on axis.This is usually not acceptable for the required cross-cockpit viewing requirements of avionics. Hence,avionics AMLCDs typically use custom high-luminance backlight system designs and wide dynamicrange (~3,000–1) dimming circuitry. Because color is used to convey safety-related information, the R, G,B chromaticity specifications for avionics displays are very tight and may require custom-saturated colorfilters at the expense of some reduction in optical efficiency of the system. This is in contrast to consumerdisplays such as notebook-PC displays that typically use less-saturated colors to achieve high opticalefficiency and longer battery life.

Specular reflections are a key concern for cockpit AMLCDs because of sunlight readability require-ments. By using low-reflectance black-matrix materials, optically matched laminations, and antireflectivecoatings, custom avionics AMLCDs can achieve overall specular reflectance of less than 0.7 %.

Cross-cockpit viewing requires wide field of view with a high contrast ratio, and gray-level luminanceand chromaticity uniformity in the field of view. Video display applications require a large number of graylevels, e.g., 8 bits, and fast response time.

Avionics displays are more susceptible to long-term image retention (LTIR) because they typicallydisplay static images over long periods of time and over extreme operating temperatures. Minimizing thepropensity for LTIR requires special design considerations as discussed in section “AMLCD Technology/


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Design Considerations.” NVIS performance, required for military and law-enforcement applications, isachieved with appropriate optical filters placed between the backlight system and the LC cell in theAMLCD stack and/or by using a secondary backlight source especially tuned for NVIS night operation.

Environmental Performance RequirementsAvionics displays are tested for performance under a variety of environmental parameters. Generally,standard tests such as RTCA DO-160 (for commercial) and MIL-STD-810 (for military) are used toqualify the display for environmental performance. The performance requirements to be met over theenvironmental conditions are defined in SAE AS8034B (commercial), and military requirements areprogram dependent. Electronic displays face significant challenges in order to be viewable, usable, andsafe in flight deck applications. Often operating anywhere in the world, and at a wide range of pressurealtitudes, aircraft are subjected to extremes of temperature, humidity, and atmospheric pressure. This,combined with consideration for failures of equipment cooling systems and aircraft pressurizationsystems, places stringent requirements on the robustness of the design of the electronic display systemcomponents. Some of the important environmental parameters include:

• Temperature range– Operating (�40 �C to 71 �C)– Storage (�50 � C to 85 �C)

• Thermal shock• Humidity (to 100 % RH)• Salt atmosphere• Ambient lighting (dark to direct sunlight)• EMI (susceptibility and emissions)• Mechanical shock and vibrations• Explosive decompression• Altitude

For compliance with these stringent environmental performance requirements, avionics displays areruggedized using various enhancement components as shown in Fig. 4, which illustrates a typical avionicsAMLCD stack.

The high operating temperature requirement is achieved by using (1) a liquid-crystal material with ahigh clearing temperature and (2) an active-matrix array designed for high-temperature operation. Thelow-operating-temperature requirement (approximately �40 �C) is met by using an integrated heater toachieve adequate LC response time at low operating temperatures. An ITO heater glass is placed behindthe LC cell to heat the display when the ambient temperature is less than about 0 �C. The temperatureinside the display will be higher than the ambient temperature because of the high-luminance backlightand low transmission efficiency of the color AMLCD. Because some cockpits do not provide for forced-air cooling, the display packaging and integration must be designed with good thermal management inmind to reduce the actual display temperature.

Flight decks are subject to a wide range of mechanical motions, from low-frequency effects ofturbulence to high-frequency engine vibrations, to shocks and accelerations associated with emergencyoperations and gunfire for military applications. The flight deck displays must continue to presentviewable, useful information to the pilots through all these conditions. In addition to robust electronicand mechanical/packaging designs, displayed images must achieve adequate image and informationrefresh rates to maintain smooth presentation of information to the pilots. The display-driver-assemblypackaging contains the critical elements with respect to mechanical stress. The tape-automated bond


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(TAB) bend window and die-interlead bonds are especially fragile. The bend window consists of finecopper leads which are typically several tens of micrometers wide and provides electrical connectionsbetween the LCD and the printed wiring board (PWB). The display packaging must tightly constrain therelative position of the PWBs and the glass, indeed, all elements of the display stack, to meet the shock andthe vibration requirements. A protective coating is typically applied to the dies and bend windows.Similarly, the display-package design must take into account the explosive-decompression and high-altitude requirements.

Design issues for operation under high humidity include (1) maintaining the integrity of cell seal and fillport, (2) protecting the polarizer, (3) preventing delamination between different lamination components(such as the cover glass and polarizer and the polarizer and LC cell), and (4) passivating the exposedelectrode surfaces. For protection against salt atmosphere, the critical areas requiring protection arelocated outside the LC cell. These include the metal bond pads and the TAB bond regions, which mustbe passivated.

Aircraft flight decks can be very brightly illuminated in daytime conditions due to the need for the pilotsto have adequate visibility of the external environment via generous window areas and, in some cases,bubble canopies. Other factors include higher-intensity sunlight due to aircraft flight altitudes, reflectionsand light diffusion from clouds, and “shafting” of direct sunlight impinging on the displays (e.g., throughside windows). The illumination levels in cockpits can range from dark (~1 fC) to direct sunlight of~10,000 fC. Night flight operations present additional challenges. To maintain pilots’ night-adaptedvision so that they can see the outside environment, flight deck light levels, including the instruments,must be adjustable to levels sufficiently low so as to not disrupt the pilots’ night vision. Flight deckdisplays must achieve this while maintaining image clarity, color differentiation, viewing angle, and otherreadability requirements. This, when combined with the high ambient light requirements for daytimeoperations, requires the displays to be capable of extremely wide dimming ratios (>2000:1). In flight

Fig. 4 Schematic stack-up of an avionics AMLCD showing various elements of the display


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decks with night vision systems, the displays must be compatible with the light spectrum sensitivities ofthe night vision system so as not to interfere with its operation.

Controlling radiated emissions (RE) from the flight deck displays involves design trade-offs to meet theavionics EMI requirements of MIL-STD-461 and RTCA/DO-160. The design considerations are EMIlevels, display size, drive method, controller type and location, line termination, and ground decoupling.An ITO shield plane may be needed to meet the EMI requirements, but this could reduce opticalperformance by increasing reflectance unless an antireflection (AR) coating is used in conjunction withthe EMI coating. Also, aircraft systems include elements that can be susceptible to conducted and/orradiated electromagnetic energy. The flight deck display system must be designed to prevent the emissionof such potentially disruptive electromagnetic interference (EMI) energies and must also survive andoperate when exposed to the energy levels expected in the aircraft, from both on-aircraft and externalsources. In addition to the standard EMI requirements described above, avionics displays must also meetenvironmental requirements relating to immunity from lightning and high-intensity radiated fields (HIRF)interference.

Display Technology Options

CRT displays enabled the “glass cockpit” and dominated the flight deck display market until themid-1980s. They still continue to be used in legacy aircraft flight decks, even though it is becomingmore and more challenging dealing with rapidly decreasing CRT manufacturing sources. Starting in thelate 1980s, AMLCD (active-matrix liquid-crystal display) has been and continues to be the technology ofchoice for committing to new flight deck designs, because of their unique advantages of lower weight andpower consumption, flat form factor, and enhanced reliability. Additional advantages of AMLCDs overCRTs for cockpit applications include higher luminance, luminance uniformity, wide dimming range,sunlight readability, fault tolerance, and a large active display area with a small border near the bezel.Compared to the notebook-PC displays and desktop monitors, cockpit applications represent anextremely challenging environment for the AMLCDs as discussed in section “Performance Requirementsof Avionic Displays.”

While AMLCDs are intrinsically superior to CRTs for cockpit displays, initially their design,manufacturing, and successful integration in airborne environments were highly demanding and requiredcustom designs. As AMLCD technology continued to mature and to be developed for other demandingand higher volume applications such as industrial and automotive, displays developed for these applica-tions were found to be suitable for further ruggedization (semi-custom design) for use in flight deckapplications as opposed to the full custom designs employed in early times. In the following, AMLCDdesign considerations for use in flight deck applications are discussed first, followed by a discussion ofprojection displays as a candidate for use in flight deck applications and the emerging AMOLED (active-matrix organic light-emitting diode) and flexible display technologies that have a potential for use as next-generation flight deck displays.

AMLCD Technology/Design Considerations

LCD ModeThe LCD mode has a major influence on the optical performance of the display. It impacts the contrastratio, luminance, efficiency, response time, and viewing angle. During the early period of the AMLCDtechnology development, the avionics industry had to focus on the development of wide-viewing-angletechnology (Sarma et al. 1990; Sarma et al. 1991), as it was not a priority for the commercial display


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industry which was focused on consumer notebook-PC screen applications. The first wide-viewing-angleAMLCD for avionics displays was based on normally black (NB), multi-gap TN (twisted-nematic) modewith halftone grayscale and was developed for the Boeing 777, which started revenue flights in 1995(Sarma et al. 1990; Sarma et al. 1991; McCartney 1994; Haim et al. 1994).

Having successfully established the market for AMLCDs for the notebook-PC applications, thecommercial industry made major efforts to improve viewing angle to address the opportunities in desktopmonitor market and achieved impressive results. Several new wide-viewing-angle LC modes have beendeveloped, including compensated normally white (NW) TN mode (Mori et al. 1997), in-plane switching(IPS) mode (Ohta et al. 1995; Endoh et al. 1999), and multi-domain vertically aligned (MVA) mode(Takeda et al. 1998). Subsequently, these LC modes were further refined for the monitor and large screenTVapplications.

In the compensated NW (normally white) TN mode, the positive birefringence of the twisted-nematicLC layer is compensated by a discotic polymer compensation film (Fuji wide-view film) with a tilted opticaxis to achieve a wide viewing angle (Mori et al. 1997). This approach achieves significant expansion ofthe viewing angle in the horizontal direction and some expansion in the vertical direction. The viewingangle in the negative vertical direction is still very limited by gray-level inversion. Fortunately, severalavionics applications generally do not require large negative vertical viewing angles. Displays for theSpace Shuttle (Fig. 1c) were a notable exception, as they required a wider vertical viewing angle,including in the negative vertical direction, and thus used the custom NB, multi-gap, TN (twisted-nematic) mode with halftone grayscale displays that were initially designed and developed for B777.

In-plane switching (IPS) mode (Ohta et al. 1995; Endoh et al. 1999) uses interdigitated pixel electrodesto rotate the director of the homogeneously aligned liquid crystal along the in-plane field direction tomodulate the backlight. The IPS mode uses an NB mode and crossed polarizers and achieves a very wideviewing angle (�80� with CR > 10:1). During early development of the IPS mode, the transmissionthrough the pixel was lower because of the interdigitated electrodes that were opaque, and the switchingspeed was slow (~70 ms). Also, it had some chromaticity shifts (yellow shift and blue shift) at low graylevels. However, use of the dual-domain IPS mode solved the color-shift problem and achieved remark-ably wide viewing angle with superior color stability and image quality. Also, by optimizing the LCmaterial and design, < 10-ms response time has been achieved. IPS mode has been successfully adaptedfor the flight deck displays, first in 1998 (Kobayashi et al. 1998). In recent years, IPS mode has beenhighly refined, with variations of this mode such as fringe field switching (FFS) mode (Lee et al. 2006)utilizing transparent interdigitated ITO electrodes separated by a dielectric and very little gap betweenthem. The FFS mode achieves high pixel aperture ratio (higher display efficiency) and fast response timeand facilitates higher pixel resolutions, such as in high-resolution smartphones with eye-limitingresolutions.

The MVA (multi-domain vertical alignment) mode uses homeotropic alignment and a liquid-crystalmaterial with a negative dielectric anisotropy (Takeda et al. 1998). Because of the vertical alignment andthe NB mode used, this mode achieves a remarkably good black state and high on-axis contrast ratio(~1,000:1). The VA mode can be compensated using a simple negative retardation film to achieve a wideviewing angle, and biaxial compensation films can further enhance the viewing angle. The multi-domainconfiguration produces good viewing angles, in both the horizontal and vertical directions with no gray-level inversion. MVAmode has also been successfully adapted for the flight deck display applications, forthe first time in 2003 (Sarma et al. 2003).

Currently, IPS and MVA modes are highly advanced and utilized in large screen TVapplications. TheLCDmode to be selected depends on the required display performance. For example, for a military fightercockpit display application, the conventional TN mode may be a perfect choice because a very wide


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viewing angle is not required. Wide-body aircraft flight decks requiring wide viewing angles utilizeadvanced IPS (FFS) and MVA mode LCDs.

Colorimetric DesignThe AMLCD color gamut depends primarily on the emission spectrum of the backlight and thetransmission spectrum of the color filters used. But the influence of other optical elements – such asantireflection coatings and compensation films in the optical stack – should not be neglected, particularlyfor off-axis performance. The primary consideration in the selection of color filters, apart from matchingthem to the backlight emission spectrum, is the trade-off between transmission and color gamut. Thedenser the color filter, the more saturated the colors will be, but the transmission will be lower. In avionicsdisplays, generally, the choice is to achieve saturated colors and a larger color gamut.

Long-Term Image Retention LTIR:LTIR occurs when AMLCDs are driven with static images over extended periods of time. The static imageis retained on the display even after the initial image is removed and replaced with a new image. Thelength of time the previous image is retained can vary from seconds to days, depending on the severity ofthe problem. A second kind of image retention – short-term image retention (STIR) – may persist forseveral seconds. STIR is due to the formation and annihilation of a disclination in the pixel region, as thepixel is switched. The disclination line typically forms at the corner of each pixel corresponding to the tailof the rubbing direction. This problem is solved by masking the region of the pixel where the disclinationforms, with black matrix with an associated loss of some pixel aperture ratio and transmission, or byreducing the lateral electric fields at the pixel by appropriate pixel design and layout.

Avionics displays are very susceptible to LTIR, since certain regions of the display have static imageryfor extended periods of time (e.g., several hours) during long-duration flights. The high operatingtemperatures further increase the susceptibility of avionics AMLCDs to LTIR. In contrast, consumerAMLCDs rarely have the same image displayed for extended periods of time (screen savers help here),and typically operate at room temperature, and thus have a very small susceptibility to LTIR.

The LTIR phenomenon in AMLCDs is due to charge buildup and retention in the pixel dielectrics,which can be caused by DC driving of the pixel. When the LCD is driven with a net DC voltage, DCcharge can accumulate in some of these dielectric layers and produce an internal potential in the liquidcrystal, resulting in a change in transmission and thus a retained image. The analysis of the LTIRphenomenon in a given AMLCD can be quite complex because it depends on many factors such asAMLCD design conditions, impurities in or characteristics of the materials – liquid crystal, alignmentlayer, and passivation layer – used in the display panel, processing conditions, and display drivingconditions. Significant progress has been made in recent years, through materials and process and designoptimization, to dramatically reduce the propensity of flight deck displays for LTIR.

Backlight TechnologiesBacklight is a critical component of the AMLCD. Generally the backlight systems for the flight deckdisplays are custom designed to achieve the required chromaticity coordinates, high luminance, dimmingrequirements, lifetime, and reliability. Initially, the AMLCD backlight systems used cold cathodefluorescent lamps (CCFL). However, as CCFL lamps were difficult to dim, avionics applications focusedon the development of hot cathode fluorescent lamps (HCFL) to achieve the required wide dynamic rangedimming (>2,000:1). Subsequent development and commercialization of high-efficiency LEDs (light-emitting diodes) with high luminance, long lifetime, and reliability facilitated their use in LCD backlights.LED backlights have given a significant boost to AMLCDs in reducing the performance gap againstemerging OLED (organic light-emitting diode) display technology (see section “AM OLED


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Technology”). High-efficiency white LEDs are achieved using a blue LED and a high-efficiency yellowphosphor. For more precise control of the chromaticity to achieve the desired requirements, a mixture ofwhite and individual color (such as red) LEDs may be utilized in the backlight design. Also, as the LEDswitching time is of the order of microseconds, dynamic backlight mode can be employed to enhance thedisplay contrast.

Quantum dot (QD)-enhanced backlight is a recent development for AMLCDs (Steckle et al. 2014).Compared to a conventional LED backlight using a white LED or R, G, B LED elements, a QD-enhancedbacklight system uses a blue LED array and a QD encapsulated film (sheet) between the LED array andthe LCD cell. The desired amount of blue light from the blue LEDs is upconverted to green and red colorsby the appropriately sized and spaced QDs in the QD film. The major advantage of the QD approach is toenhance the color gamut of the display, as the QDs upconvert blue wavelength to red and green emissionswith a very narrow band. Using this technology, up to 100 % sRGB color gamut has been achieved,nearing the color gamut achievable by an OLED. The QD backlight design optimization involves trade-offs between power consumption and color gamut. However, the suitability of the QD backlighttechnology for flight deck displays remains to be tested and validated.

Display Packaging and IntegrationVarious external components are added to the LCD cell to achieve the required environmental and opticalperformance (as shown in Fig. 4). The backlight system – consisting of the LEDs, backlight cavity,dimming control circuitry, diffuser, NVIS filters, and brightness enhancement and polarization-recyclingfilms – is a crucial part of the display system. Similarly, the heater glass between the backlight and the LCcell and the cover glass in front of the LC cell are also very important. Efficient optical coupling is neededbetween the various components of the display system and can be obtained by use of index-matchedlamination materials and antireflection coatings. The display packaging design must ensure that thesystem meets the mechanical-stress (shock, vibration, explosive decompression, and altitude), thermal-shock, and EMI requirements.

Projection DisplaysProjection display technology has been evaluated as an alternative to direct view flat panel displays foravionics applications in the past (Steckle et al. 2014). At that time, the rationale for projection displaydevelopment for avionics displays was mainly due to the expected future difficulties in developingAMLCDs with a variety of custom sizes and aspect ratios (mostly square), in small quantities withstringent performance requirements at a reasonable cost. Projection display technology offered a potentialpath to develop flight deck displays with the required size and aspect ratio, at low volumes, using standard(commercial off-the-shelf (COTS)) light valves (such as liquid crystal on silicon (LCOS) or digitalmicromirror device (DMD)) and other optical components. The challenges associated with this develop-ment included development of reliable and efficient projection light sources and the illumination system,projection screens required for achieving the image quality competitive with the direct view AMLCDs,and meeting other environmental requirements, including shock and vibration. Since the beginning of theavionics projection display investigations, continued development and advancements in AMLCD tech-nology with respect to performance improvements and cost reductions, and the lack of adequate progresson resolving projection display development challenges, interest in projection display approach for flightdeck applications has decreased dramatically. More recently, there is renewed interest in the rearprojection display approach for avionics (Cuypers et al. 2012; Retrieved from https://www.thalesgroup.com/sites/default/files/asset/document/ODICIS%20Datasheet.pdf), using tiled, multiple short-throw,wide angle projectors, under the European Project ODICIS (One DIsplay per Cockpit Interactive


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Solution), to develop a single large area display of arbitrary shape and curved surfaces to fit the flight deck,using multiple light valves (e.g., LCOS image sources and a LED back illumination system).

AMOLED TechnologyAMOLED has been under active development for more than 15 years, as a next-generation flat paneldisplay technology. Unlike an AMLCD, the AMOLED is an emissive display and does not require abacklight and the associated backlight system components or color filters. Thus, the AMOLED has farfewer components as illustrated in Fig. 5, with a potential for significant cost savings. Also, as the OLEDis an emissive device, it can have a better black state with a very high contrast, and its viewing angleperformance is intrinsically excellent. Further, because of the faster switching speed (tens of microsec-onds for an OLED versus several milliseconds for an LCD) OLED has superior video performancecompared to an LCD. Also, the OLED has a potential for lower power consumption as the power lossesdue to color filter absorption can be eliminated and power is dissipated only by the pixels that are switched“on,” unlike in an LCD. In addition, the OLED has a superior potential for enabling flexible displays dueto its solid state.

In spite of the OLED’s advantages of superior viewing angle and video image quality, and the potentialfor lower cost and power consumption, it has taken a long time to overcome the technology andmanufacturing challenges to be viable and achieve market success. A first AMOLED product (displayin a DSC (Digital Still Camera)) was introduced in 2003 by Sanyo-Kodak. Subsequent product intro-ductions included a 3.8” display for a PDA, an 11” display for a TV by Sony, a 15” display for a TV by LGDisplay, and a variety of specialized professional OLED monitors up to ~25” size, by Sony. All theseAMOLED-based products had varying degrees of market success. The main reason for this is that OLEDshave been competing with LCDs for essentially the same applications (i.e., displays for mobile electronicdevices, desktop monitors, and TVs). It had been a competition with a moving target of the AMLCD,which made remarkable progress during same time frame with respect to image quality, cost, anddeveloping huge infrastructure for very large mother glass size (e.g., Gen 10 Fabs with a mother glasssize of ~3 m � 3 m). For example, optimizing the LCD modes and replacing the fluorescent backlightwith an LED backlight has allowed remarkable improvements to the viewing angle and image quality ofAMLCDs in recent times. While an AMLCDwith an LED backlight can realize significant improvementsin contrast ratio and power savings by implementing local area dimming, the AMOLED takes this conceptto the ultimate with each pixel in the display possessing the capability for dimming.

Fig. 5 Schematic structure of an AMOLED display illustrating its simplicity compared to that of an AMLCD


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During the past couple of years, AMOLED has had a remarkable commercial success in high-performance displays for the smartphone and tablet applications. This commercial progress is due tothe dramatic advances in the enabling technologies, including efficiency and lifetimes for the R, G,B OLED emitters, TFT backplane technology, and OLED manufacturing technologies and infrastructuredevelopment.

OLEDs offer unique advantages as well as challenges in their use as flight deck displays. In addition tothe superior wide-viewing-angle image quality and SWaP attributes, the optical performance of OLEDs istemperature independent, unlike an LCD. It does not require a heater to maintain the response time at lowtemperatures and the contrast does not decrease at elevated temperatures as in an LCD. The sunlightreadability challenge for OLEDs can be successfully addressed (Sarma et al. 2012) by reducing theirreflectivity by use of antireflective coatings. One remaining challenge for adapting OLEDs broadly asflight deck displays is the requirement for further improvement in the lifetime of OLED devices,particularly for blue OLED emitters, to reduce the susceptibility for retained images (long-term imageretention).

Flexible DisplaysFlexible AMOLED displays have made remarkable progress in recent times and are beginning to becommercialized for some consumer applications such as smartphones, for example, by LG Display(Retrieved from http://www.lg.com/us/mobile-phones/gflex). The flexible AMOLED is fabricated on avery thin (~0.1 mm) flexible plastic film (unbreakable, unlike a glass substrate). In addition to the verythin, lightweight, and unbreakability attributes, flexible displays can be configured to conform to a desiredshape such as a flight deck to achieve enhanced display real estate. Continuing developments in flexibledisplays offer the potential for their use in next-generation flight decks.

Touch Screen User Interface

Widely popularized in recent years by smartphones and tablet computers, touch screen controls arebecoming highly accepted as a display interaction modality. This has resulted in an expectation by pilotsof touch screen controls in the flight deck. Touch screen advantages include the direct interaction withdisplayed parameters/controls, software flexibility of controls, and more intuitive manipulation of thedisplayed information. Touch gestures such as tap, swipe, pinch, and scroll are now widely familiar andare candidates for use in the flight deck. However, vibrations and turbulence are common in the flight deckand can compromise the pilot’s ability to accurately use such gestures.

Avionics Display System Design and Integration Considerations

Electronic displays in the flight deck are capable of presenting a tremendous amount of information to thepilots that varies from low-importance advisories to flight critical parameters that, if lost or are erroneous,could jeopardize the expensive aircraft and the lives of its occupants. For example, in instrumentmeteorological conditions (IMC), the pilots rely solely on their instruments for situational awareness.Misinterpretation, incorrect display, or complete loss of parameters such as aircraft pitch and roll canresult in loss of controllability of the aircraft and so must be prevented.

System design and verification play a crucial role in ensuring that these aspects are appropriatelyaddressed. Human factors methodologies help to ensure that the information presented can be properlyabsorbed and understood by the pilots. Input sensor comparisons, monitoring of hardware and software


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functions, and levels of design assurance appropriate to the safety implications of the functions areimportant in preventing the display of incorrect or hazardously misleading information to the pilots. Lossof important information is addressed through analysis of failure modes/effects, hardware failure rates,redundancy, and independence of backup systems (including possibly dissimilarity between primary andbackup systems to prevent total loss of function due to generic/design faults).

In addition to addressing flight safety system design considerations, the flight deck display systemmustalso be designed to support the business objectives of the aircraft operator. For many operators this willfocus onmaximizing the likelihood that the aircraft is capable of dispatching for a flight/mission when it isneeded. Flight deck display systems are often designed with sufficient redundancy such that the aircraftcan dispatch even with some of the system elements failed. Electronic displays and associatedmultifunctional controllers (e.g., cursor control devices and keyboards) are well suited for redistributingfunctions following the failure of some system elements to remaining operational units.

Human Factors

Electronic displays in the flight deck, as with all flight deck systems, must be validated to accomplish theirintended functions. Human factors has emerged in recent years as a discipline of increasingly importantemphasis in establishing functional and user interaction requirements. With their advantages of increasedgraphical capability, integration of information/control, flexibility, and upgradability, electronic displaysystems promise a wide range of functional possibilities.

However, the safety considerations of the flight deck mandate a careful, methodical, and scientificapproach to assessing and validating the design of the electronic displays systems from the pilot’sperspective. Thoughtful decomposition of flight deck function requirements, and the allocation of thoserequirements to systems that include the electronic displays and their associated controls, is an importantfirst step in the design process. Throughout development, the needs of the pilots and the ramifications ofdesign decisions on their ability to perform flight deck tasks must be addressed through methods such asanalyses and empirical human factors experiments. Of particular importance are assessments of pilotworkload (for both normal and abnormal situations), the propensity for errors, and pilot fatigue.

Electronic displays have facilitated great strides in the capabilities, efficiencies, and safety of the flightdeck through its human occupants, the pilots. As aircraft operational environments (e.g., NextGen andSESAR) become increasingly more complex and demanding in the future, opportunities will continue toarise for leveraging continuing advances in displays and user interface technologies for the next-generation flight deck designs. With a focus on human factors and system design, effectively leveragingthe next-generation display and user interfaces for the development of next-generation flight decks willimprove upon the already stellar safety and efficiency performance of today’s aviation.

Further Reading

Cuypers D et al (2012) Projection technology for future airplane cockpits. In: IDW 2012Endoh S, Ohta M, Konishi N, Kondoh K (1999) Advanced 18.1 inch Super TFT LCD with mega-wide

viewing angle and fast response speed of 20 ms. In: IDW ’99, p 187Federal Aviation Administration (2002) Function and installation (14 CFR 25.1301). Retrieved from

http://www.gpo.gov/fdsys/pkg/CFR-2002-title14-vol1/xml/CFR-2002-title14-vol1-sec25-1301.xmlHaim E, McCartney R, Penn C, Inada T, Unate U, Sunata T, Taruta K, Ugai Y, Aoki S (1994) Full color

grayscale LCD with wide viewing angle for avionics applications. In: SID ’94, application digest, p 23


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http://www.gpo.gov/fdsys/pkg/CFR-2002-title14-vol1/xml/CFR-2002-title14-vol1-sec25-1301.xml

Kalmansh M, Tomkins R (2000) Projection display technology for avionics applications. In: HopperD (ed) Cockpit displays VII, SPIE, April 2000

Kobayashi K, Masutani Y, Nakashima K, Nivano Y, Nishimura M, Tahata S, Mori Y, Lamberth L,Laddu R, Coyle M, Komenda V, Esposito C, Sarma K (1998) IPS-mode TFT-LCDs for aircraftapplications. In: SID ’98 digest, pp 70–73

Lee KH, Kim HY, Park KH, Jang SJ, Park IC, Lee JY (2006) A novel outdoor readability of portableTFT-LCD with AFFS technology. In: SID digest ’06, p 1079

McCartney JA (1994) The primary flight instruments for the Boeing 777 airplane. SPIE, cockpit display,vol 2219, p 98

Mori H et al (1997) Conference record. In: International display research conference (SID), p M-88Ohta M, Oh-e M, Kondo K (1995) Asia display ’95, p 707Sarma KR, Franklin H, Johnson M, Frost K, Bernot A (1990) Grayscale in AMLCD panels with wide

viewing angles. Proc Soc Inform Disp 31(1):7Sarma KR,McCartney RI, Heinze B, Aoki S, Ukai Y, Sunata T, Inada T (1991) Awide viewing angle 5-in

diagonal AM LCD using halftone grayscale. In: SID Digest ’91, p 555Sarma KR, Laddu R, Harris D, Lamberth L, Li WY, Chien CC, Chu CY, Lee CS, Wei CK, Kuo CL

(2003) MVA-AM LCD development for avionic applications. In: IDMC 2003, p 211Sarma KR et al (2012) Recent advances in AM OLED technologies for application to aerospace and

military systems. In: 2012 SPIE DSS conference proceedings, Baltimore, 23–27 April 2012Steckle JS et al (2014) Quantum dots: the ultimate down-conversion material for LCD displays. In: SID

2014 digest, p 130Takeda A, Kataoka S, Sasaki T, Chida H, Tsuda H, Ohmuro K, Sasabayashi T, Koike Y, Okamoto

K (1998) A super-high image quality multi-domain vertical alignment LCD by new rubbing-lesstechnology. In: SID ’98 digest, p 1077


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