Control and Display Technologies:

Multifunction CRT display system:

The MCDS on the orbiter crew compartment flight deck allows onboard monitoring of orbiter systems, computer software processing and manual control for flight crew data and software manipulation.

The system is composed of three types of hardware: display electronics units; display units that include the CRTs; and keyboard units, which together communicate with the GPCs over the display/keyboard data bus network.

The MCDS provides almost immediate response to flight crew inquiries through displays, graphs, trajectory plots and predictions about flight progress. The crew controls the vehicle system operation through the use of keyboards in conjunction with the display units. The flight crew can alter the system configuration, change data or instructions in GPC main memory, change memory configurations corresponding to different mission phases, respond to error messages and alarms, request special programs to perform specific tasks, run through operational sequences for each mission phase and request specific displays.

Three keyboards are located on the flight deck: two on the left and right sides of the flight deck center console (panel C2) and one on the flight deck at the side aft flight station (panel R12). Each consists of 32 momentary double-contact push button keys. Each key uses its double contacts to communicate on separate signal paths to two DEUs. Only one set of contacts on the aft station keys is actually wired because this keyboard can communicate with only the aft display electronics unit.

There are 10 number keys, six letter keys (used for hexadecimal inputs), two algebraic keys, a decimal key, and 13 special key functions. Using these keys, the flight crew can ask the GPC more than 1,000 questions about the mission and condition of the vehicle.

Each of the four DEUs responds to computer commands, transmits data, executes its own software to process keyboard inputs and sends signals to drive displays on the CRTs (or display units). The four DEUs store display data, generate the GPC/keyboard unit and GPC/display unit interface displays, update and refresh on-screen data, check keyboard entry errors and echo entries to the CRT (or DU).

There are three CRTs (or display units) on flight deck forward display and control panel F7 and one at the side aft flight deck station on panel R12. Each CRT is 5 by 7 inches.

The display unit uses a magnetic-deflected, electrostatic-focused CRT. When supplied with deflection signals and video input, the CRT displays alphanumeric characters, graphic symbols and vectors on a green-on-green phosphorous screen activated by a magnetically controlled beam. Each CRT has a brightness control for ambient light and flight crew adjustment.

The DEUs is connected to the display/keyboard data buses by multiplexer interface adapters that function like those of the GPCs. Inputs to the DEU are from a keyboard or a GPC. The CRT switches on panel C2 designate which keyboard controls the forward DEUs and CRT (or DUs). When the left CRT sel switch is positioned to 1, the left keyboard controls the left CRT 1; if positioned to 3, it controls the center CRT 3. When the right CRT sel switch is positioned to 2, the right keyboard controls the right CRT 2; if positioned to 3, it controls the center CRT 3. If the left CRT sel and right CRT sel switches are both positioned to 3, keystrokes from both keyboards are interleaved. Thus, flight crew inputs are made on the keyboards and data is output from the GPCs on the CRT displays.

The aft station panel R12 keyboard is connected directly to the aft panel R12 DEU and CRT (or DU); there is no select switch.

Each DEU/DU pair, usually referred to as a CRT, has an associated power switch. The CRT 1 power , on , stby , off switch on panel C2 positioned to stby or on allows control bus power to activate RPCs and sends MNA power to DEU/ DU 1. The stby position warms up the CRT filament. The on position provides high voltage to the CRT. The CRT 2 switch on panel C2 functions the same as the CRT 1 switch, except that CRT 2 is powered from MNB. The CRT 3 switch on panel C2 functions the same as the CRT 1 switch, except that CRT 3 is powered from MNC. The CRT 4 switch on panel R12 functions the same as the CRT 1 switch, except that CRT 4 is powered from MNC. The respective keyboards receive 5 volts of ac power to illuminate the keys. Each DEU/DU pair uses about 300 watts of power when on and about 230 watts in standby.

The CRT 1, 3, 2, major func, GNC, SM and PL switches on panel C2 tell the GPCs which of the different functional software groups is being processed by the keyboard units and what information is presented on the CRT. The CRT 4, major func, GNC, SM and PL switches on panel R12 function in the same manner.

Positioning the display electronics unit 1, 2, 3, 4 switches on panel O6 to load initiates a GPC request for data stored in mass memory through a GPC before operations begin. The information is sent from the mass memory to the GPC and then loaded from the GPC into the DEU memory.

It is possible to do in-flight maintenance and exchange DU 4 with DU 1 or 2. DU 3 cannot be changed out because of the control and display panel configuration. Also, either forward keyboard can be replaced by the aft keyboard. The DEUs is located behind panels in the middeck. DEUs 1 and 3 are on the left, and DEUs 2 and 4 are on the right. DEU 4 can replace any of the others; however, if DEU 2 is to be replaced, only the cables are changed because 2 and 4 are next to each other.

The DEUs and DUs are cooled by the cabin fan system. The keyboard units are cooled by heat dissipation.

Special Purpose Diodes

The unique characteristics of semiconductor material have allowed for the development of many specialized types of diodes. A short description of some of the more common diode types is given for general familiarization. Figure 10-205 illustrates the schematic symbols for some of the special purpose diodes.

Light-Emitting Diode (LED)

In a forward biased diode, electrons cross the junction and fall into holes. As the electrons fall into the valence band, they radiate energy. In a rectifier diode, this energy is dissipated as heat. However, in the light-emitting diode (LED), the energy is dissipated as light. By using elements, such as gallium, arsenic, and phosphorous, an LED can be designed to radiate colors, such as red, green, yellow, blue and inferred light. LEDs that are designed for the visible light portion of the spectrum are useful for instruments, indicators, and even cabin lighting. The advantages of the LED over the incandescent lamps are longer life, lower voltage, faster on and off operations, and less heat.

Liquid Crystal Displays (LCD)

The liquid crystal display (LCD) has an advantage over the LED in that it requires less power to operate. Where LEDs commonly operate in the milli-watt range, the LCD operates in the microwatt range. The liquid crystal is encapsulated between two glass plates. When voltage is not applied to the LCD, the display will be clear. However, when a voltage is applied, the result is a change in the orientation of the atoms of the crystals. The incident light will then be reflected in a different direction. A frosted appearance will result in the regions that have voltage applied and will permit distinguishing of numeric values.


Thermal energy produces minority carriers in a diode. The higher the temperature, the greater the current in a reverse current diode. Light energy can also produce minority carriers. By using a small window to expose the PN junction, a photodiode can be built. When light fall upon the junction of a reverse- biased photodiode, electrons-hole pairs are created inside the depletion layer. The stronger the light, the greater the number of light-produced carriers, which in turn causes a greater magnitude of reverse-current. Because of this characteristic, the photodiode can be used in light detecting circuits.


The varactor is simply a variable-capacitance diode. The reverse voltage applied controls the variable capacitance of the diode. The transitional capacitance will decrease as the reverse voltage is increasingly applied. In many applications, the varactor has replaced the old mechanically tuned capacitors. Varactors can be placed in parallel with an inductor and provide a resonant tank circuit for a tuning circuit. By simply varying the reverse voltage across the varactor, the resonant frequency of the circuit can be adjusted.

Schottky Diodes

Schottky diodes are designed to have a metal, such as gold, silver, or platinum, on one side of the junction and doped silicon, usually an N-type, on the other side of the junction. This type of a diode is considered a unipoler device because free electrons are the majority carrier on both sides of the junction. The Schottky diode has no depletion zone or charge storage, which means that the switching time can be as high as 300 MHz. This characteristic exceeds that of the bipolar diode.

Plasma Panels:

A plasma display panel (PDP) is a type of flat panel display common to large TV displays 30 inches (76 cm) or larger. They are called “plasma” displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent lamps.

  • Picture quality
    • Capable of producing deeper blacks allowing for superior contrast ratio
    • Wider viewing angles than those of LCD; images do not suffer from degradation at high angles like LCDs.
    • Less visible motion blur, thanks in large part to very high refresh rates and a faster response time, contributing to superior performance when displaying content with significant amounts of rapid motion.
  • Earlier generation displays were more susceptible to screen burn-in and image retention, recent models have a pixel orbiter that moves the entire picture slower than is noticeable to the human eye, which reduces the effect of burn-in but does not prevent it.
  • Due to the bistable nature of the colour and intensity generating method, some people will notice that plasma displays have a shimmering or flickering effect with a number of hues, intensities and dither patterns.
  • Earlier generation displays (circa 2006 and prior) had phosphors that lost luminosity over time, resulting in gradual decline of absolute image brightness (newer models may be less susceptible to this, having advertised lifespans exceeding 100 000 hours, far longer than older CRT technology).
  • Screen-door effects (black lines between rows of pixels) become noticeable on screen sizes larger than 127 cm (50 in); the effect is more visible at shorter viewing distances.
  • Other
    • Use more electrical power, on average, than an LCD TV.
    • Does not work as well at high altitudes above 2 km due to pressure differential between the gases inside the screen and the air pressure at altitude. It may cause a buzzing noise. Manufacturers rate their screens to indicate the altitude parameters.
    • For those who wish to listen to AM radio, or are amateur radio operators (hams) or shortwave listeners (SWL), the radio frequency interference (RFI) from these devices can be irritating or disabling.

Touch Screen:

Garmin has raised the bar with the announcement of the GTN 650 and GTN 750 series. These panel-mount units are certified and approved for installation in hundreds of makes and models of general aviation aircraft.

The GTN 650 and GTN 750 feature new capabilities for GPS/NAV/COM systems like touchscreen operation, graphical flight planning with victor airways and high-altitude jet routes, remote transponder, remote audio control (750 series only), Safe Taxi and electronic chart capabilities (750 series only).

“As the successors to the very popular GNS 430W and 530W, the GTN 650 and 750 have big shoes to fill. We’re confident that the GTN series will set a new standard on what avionics for general aviation aircraft should be, just as the GNS 430 and 530 did when they were announced in 1998,” said Gary Kelley, Garmin’s vice president of marketing.

“The GTN 650 and 750 are the first touchscreen avionics certified for general aviation aircraft. Although some may think the touchscreen operation is the most unique feature of these systems, we believe the interface and expansive new capabilities are even more innovative.”

The most notable physical difference between the GTN 650 and 750 is the screen size. The GTN 650 has the same exterior footprint as the GNS 430W, but has a 4.9-inch screen (diagonal) that has 53 percent more screen area than the GNS 430W.

The GTN 750’s large 6.9-inch screen (diagonal) has 98 percent more screen area than the GNS 530W, which makes it possible to view an entire chart via Garmin Flite Charts and Chart View, as well as display integrated audio and intercom functions (with the new optional GMA 35 remote mount audio processor).

In addition, both units display a greatly enhanced, higher resolution picture (GTN 650: 600×266 pixels; GTN 750: 600×708 pixel) that has over 5 times more pixels than the GNS 430W and 530W, respectively.

The touchscreen GTN 650 and 750 both feature a shallow menu structure, desktop-like menu interface with intuitive icons, audio and visual feedback, and animation so that pilots know exactly how the systems are responding to their input. The GTN has a touchscreen alphanumeric keyboard, and also utilizes a “back” icon for quick and easy operation.

Recognizing that hand stabilization will help make it even easier to enter data, both units have a finger anchoring bezel around the side of the display and fingerboard at the bottom of the screen.

For those who prefer traditional data entry via buttons and knobs, the GTN systems have a dual concentric knob for data entry, volume/squelch knob, “home” button and “direct to” button so that pilots can do all the basic fundamentals – like establish a route and change COM frequencies – without using the touchscreen. With the home key, pilots are seldom more than two taps away from all primary pages and functions.

Flight planning made easy, the GTN series offers graphical flight planning capability (patent pending) so that pilots can edit an active flight plan route on the map and easily enter a new waypoint or modify the sequence by tapping or dragging their finger on the screen. Victor airways and high-altitude jet routes can be overlaid on the moving map, and airway segments can be selected onscreen for instant entry into a flight plan.

The system has a unique “rubber band” feature that lets pilots select a flight plan leg on the screen and then alter it to accommodate a deviation or ATC amendment. In addition, pilots can pan across the map display by swiping their finger across the screen.

Enhanced situational awareness, thanks to built-in terrain, mapping and obstacle databases, the GTN provides a greatly enhanced, high resolution presentation of the surrounding area. A built-in terrain elevation database shows color-coded alerts when potential terrain conflicts are ahead.

Full Class B TAWS alerting is also available as an option. The SBAS/WAAS equipped GTN 650 and 750 let pilots fly GPS-guided LPV glide path approaches down to ILS-comparable minimums. In addition, precise course deviation and roll steering outputs can be coupled to select autopilots so that IFR flight procedures may be flown automatically.

Add weather, traffic and more because the GTN offers a wide array of compatibility with select Garmin avionics and sensors, Garmin has made it possible to have a consistent and intuitive interface to other systems – like audio and transponder – by creating simplified systems management functionality on the GTN flight deck.

Saving valuable panel space, Garmin’s new GMA 35 remote mount audio processor (optional) interfaces with the GTN 750 and makes it possible for the GTN to be used as a touchscreen control head for the aircraft’s audio and intercom functions.

The GMA 35 helps streamline cockpit communications with record/playback capability for copying clearances. It also includes an internal microphone that senses the amount of ambient noise and automatically adjusts the cockpit speaker and the headset volume based on the level of noise in the cockpit.

Garmin’s GTX 32/33/33D remote transponders (optional) also interface with the GTN 650 or 750 so that pilots can control transponder function from the GTN’s display. Optional versions of the GTX 33/33D mode S transponders are available which support ADS-B/Out.

Optional XM WX Satellite Weather™, lightning, and traffic system inputs are also supported and may be overlaid on the moving map. In addition, XM radio is available as an option (XM WX Satellite Weather™ and radio service is only available to U.S. and Canadian customers with a subscription and with an optional GDL 69 series data link receiver).

The standard GTN 650 and GTN 750 feature a 10-watt COM, and a field upgradeable 16-watt version is also available. In third quarter 2011, Garmin will make available a GTN 725, which is similar to the GTN 750, and is a GPS only unit. Also, a GTN 625 will be available that is a GPS only unit, and a GTN 635 that is a GPS unit with VHF Communications radio. All units are SBAS/WAAS enabled.

Direct voice input:

Direct voice input (DVI) (sometimes called voice input control (VIC)) is a style of human–machine interaction “HMI” in which the user makes voice commands to issue instructions to the machine. It has found some usage in the design of the cockpits of several modern military aircraft, particularly the Eurofighter Typhoon, the F-35 Lightning II, the Dassault Rafale and the JAS 39 Gripen, having been trialled on earlier fast jets such as the Harrier AV-8B and F-16 VISTA. A study has also been undertaken by the Royal Netherlands Air Force using voice control in a F-16 simulator.

The USAF initially wanted DVI for the Lockheed Martin F-22 Raptor, but it was finally judged too technically risky and was abandoned.

DVI systems may be “user-dependent” or “user-independent”. User-dependent systems require a personal voice template to be created by the pilot which must then be loaded onto the aircraft before flight. User-independent systems do not require any personal voice template and will work with the voice of any user.

In 2006 Zon and Roerdink, at the National Aerospace Laboratory in the Netherlands, examined the use of Direct Voice Input in the “GRACE” simulator, in an experiment in which twelve pilots participated. Although the hardware performed well, the researchers discovered that, before installation in a real aircraft their DVI system would need some improvement, since operation of the DVI took more time than the existing manual method. They recommended that:

  • The syntax must become simpler;
  • The recognition rate of the system must improve;
  • Response time of the system must decrease.

They suggested that all of these issues were of a technological nature and thus seemed feasible to solve. They concluded that in cockpits, especially during emergencies where pilots have to operate the entire aircraft on their own, a DVI system might be very relevant. During other situations it seemed to be interesting but not of crucial importance.

Multi-function display:

The primary flight instruments can all be displayed simultaneously on one reasonably easy-to-read video monitor much like the flat panel displays in laptop computers. These displays are called primary flight displays (PFDs). You must still cross-check around the panel and on the display, but more information is available in a smaller space in easier to read colors. These convenient displays receive data from sensors such as magnetometers or magnetic flux valves to determine heading referenced to magnetic north. The attitude (pitch and roll) of the aircraft is sensed by the attitude heading reference system (AHRS) and displayed as the attitude gyro would be in conventional instrumentation. The altitude, airspeed, and outside temperature values are sensed in the air data computer (ADC) and presented in the PFD on vertical scales or portions of circles.
The multi-function display (MFD) can often display the same information as the PFD and can be used as a backup PFD. Usually the MFD is used for traffic, route selection, and weather and terrain avoidance. However, some PFDs also accommodate these same displays, but in a smaller view due to the primary flight instrument areas already used in the display. You must learn and practice using that specific system.

It is important to be very careful in the selection (programming) of the various functions and features. In the event of failures, which have a large impact on flight safety and situational awareness, you must always be ready and able to complete the flight safely using only the standby instruments.

A multi-function display (MFD) (part of multi function structures) is a small screen (CRT or LCD) in an aircraft surrounded by multiple buttons that can be used to display information to the pilot in numerous configurable ways. Often an MFD will be used in concert with a primary flight display. MFDs are part of the digital era of modern planes or helicopter. The first MFD were introduced by air forces. The advantage of an MFD over analog display is that an MFD does not consume much space in the cockpit. For example the cockpit of RAH-66 “Comanche” does not have analog dials or gauges at all. All information is displayed on the MFD pages. The possible MFD pages could differ for every plane, complementing their abilities (in combat).

Many MFDs allow the pilot to display their navigation route, moving map, weather radar, NEXRAD, GPWS, TCAS and airport information all on the same screen.

MFDs were added to the Space Shuttle (as the glass cockpit) starting in 1998 replacing the analog instruments and CRTs. The information being displayed is similar, and the glass cockpit was first flown on the STS-101 mission.

In modern automotive technology, MFDs are used in cars to display navigation,

Head-up display:

A head-up display or heads-up display—also known as a HUD—is any transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of the name stems from a pilot being able to view information with the head positioned “up” and looking forward, instead of angled down looking at lower instruments.

Although they were initially developed for military aviation, HUDs are now used in commercial aircraft, automobiles, computer gaming, and other applications.


Other than fixed mounted HUDs, there are also head-mounted displays (HMDs). Including helmet mounted displays (both abbreviated HMD), forms of HUD that features a display element that moves with the orientation of the user’s head.

Many modern fighters (such as the F/A-18, F-16 and Eurofighter) use both a HUD and HMD concurrently. The F-35 Lightning II was designed without a HUD, relying solely on the HMD, making it the first modern military fighter not to have a fixed HUD.


HUDs are split into four generations reflecting the technology used to generate the images.

  • First Generation—Use a CRT to generate an image on a phosphor screen, having the disadvantage of the phosphor screen coating degrading over time. The majority of HUDs in operation today are of this type.
  • Second Generation—Use a solid state light source, for example LED, which is modulated by an LCD screen to display an image. These systems do not fade or require the high voltages of first generation systems. These systems are on commercial aircraft.
  • Third Generation—Use optical waveguides to produce images directly in the combiner rather than use a projection system.
  • Fourth Generation—Use a scanning laser to display images and even video imagery on a clear transparent medium.

Newer micro-display imaging technologies are being introduced, including liquid crystal display (LCD), liquid crystal on silicon (LCoS), digital micro-mirrors (DMD), and organic light-emitting diode (OLED).

Multifunctional Keypad (MFK)

The equipment in an aircraft are automatically controlled by a central computer, known as the Mission Computer (MC).
The MC interacts with the other avionics equipment through three MIL-STD-1553 communication buses. Multi Function Keyboard (MFK) is one such equipment. It is used to communicate with the pilot about the status of various equipment and the navigation.
The MFK has, at its heart, a MOTOROLA 68000 series processor with ROM, RAM and EEPROM memory to carry out its task. The MFK is the pilot interface for all communications with MC or other equipment through MC. It is connected to one of the 1553 buses, used by MC for data communication. It is also connected to the Multi Function Rotary switch (MFR) through a RS422 interface.
The MFK has a built-in display unit and a keyboard. The display unit is LCD based. The keyboard has provisions to enter alphabetic and numeric values. There are a number of control buttons to facilitate the pilot communication with MC.
The software has been developed as a real time, embedded application. The development platform includes the C Language, pSOS real-time kernel, and the 68000 series Assembly Language. Teamwork Case Tool was used during system analysis. It was also used for the preparation Software Requirement Specification.
The MFK software provides various functionalities to assist effective communication with MC. These messages are handled by MFK in the following three different modes of operations.

-Initialisation phase (Init)

-Operations Flight Program (OFP)

-Flight Line Maintenance (FLM)

The software is capable of receiving the page information from MC in binary format and validate them. Upon valid information, it converts them into pilot readable alphabetic and numeric values before displaying the page on the screen. The software can also process page requests from the pilot and send that message to MC to get the details for a new page.
The software allows the pilot to modify the flight parameters, validates the pilot input and sends them to MC for effecting the changes. The pilot can request the MC to send the status of other avionics equipment. Also, those equipment can be turned ON or OFF by the pilot depending on the need.
The system is capable of storing the data for waypoint library and airfield library. The data is sent from Mission Preparation and Retrieval Unit (MPRU). The system sends the results of the data loading to MPRU. The pilot can browse or change the waypoint library. The system also provides the ability to maintain alternate waypoints to enable the pilot to complete the mission.
The software is responsible for handling the time management functions of the MFR. It manages the real time display and the stop watch functions.
The software also has the following management functions:


-CCU communication.

-Built-in tests

During identification, MFK sends the hardware and software version number to MC. The software sends all its MC messages to Coding and Control Unit (CCU) also. This enables the CCU to take charge of the system, in case the MC fails for some reasons. The software comes with a built-in test feature to ensure its proper functioning.
The development has followed the MIL-STD-2167 standards in all its phases, such as design, development and testing.


HOTAS an abbreviation for Hands On Throttle-And-Stick, is the name given to the concept of placing buttons and switches on the throttle stick and flight control stick in an aircraft’s cockpit, allowing the pilot to access vital cockpit functions and fly the aircraft without having to remove his hands from the throttle and flight controls. Application of the concept was pioneered with the Ferranti AIRPASS radar and gunsight control system used by the English Electric Lightning[1] and is widely used on all modern fighter aircraft such as the F-16 Fighting Falcon.

HOTAS is a shorthand term which refers to the pattern of controls in the modern fighter aircraft cockpit. Having all switches on the stick and throttle allows the pilot to keep his “hands on throttle-and-stick”, thus allowing him to remain focused on more important duties than looking for controls in the cockpit. The goal is to improve the pilot’s situational awareness, his ability to manipulate switch and button controls in turbulence, under stress, or during high G-force maneuvers, to improve his reaction time, to minimize instances when he must remove his hands from one or the other of the aircraft’s controls to use another aircraft system, and total time spent doing so.

The concept has also been applied to the steering wheels of modern open-wheel racecars, like those used in Formula One and the Indy Racing League. HOTAS has been adapted for game controllers used for flight simulators (most such controllers are based on the F-16 Fighting Falcon‘s) and in cars equipped with radio controls on the steering wheel. In the modern military aircraft cockpit the HOTAS concept is sometimes enhanced by the use of Direct Voice Input to produce the so-called “V-TAS” concept, and augmented with helmet mounted display systems such as the “Schlem” used in the MiG-29 and Su-27, which allow the pilot to control various systems using his line of sight, and to guide missiles by simply looking at the target.


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