Older style instruments containing rotating mass gyros, delicate bearings, hairsprings and other extremely sensitive components have been replaced with electronic solid-state devices. The new "strap
Figure 11-64. Measurement of fuel flow based on mass is accomplished by spinning the fuel toward a turbine with an impeller.The amount the turbine is displaced depends on the quantity and viscosity of the fuel that is spun toward it.
down" systems contain no moving parts and boast of greater reliability and higher time between failures.
Electronic Flight Instruments Systems (EFIS)have several advantages over conventional instruments.
Primarily, EFIS offers the advantage of greatly increased reliability, and, ultimately, reduced main-tenance costs. EFIS also reduces instrument panel clutter by combining several instruments into one unit. A pilot can customize the information pre-sented on the displays, which can reduce workload.
Many EFIS systems offer a moving map display with superimposed weather radar information.
Collision avoidance information can even be incor-porated into certain EFIS displays. [Figure 11-65]
A typical EFIS system consists of four interchange-able CRT displays and their associated symbol gen-erators. The center symbol generator is used as a redundancy check between the left and right sys-tems. If one or more of the units fail, the other(s) will control the electronic displays. The symbol genera-tor receives signals from the various instruments and navigational sensors located throughout the aircraft.
The weather radar receiver/transmitter receives sig-nals from the aircraft's radar antenna and sends information to both the pilot and copilot's symbol
Figure 11-65.This two tube EFIS display is set up to display attitude information on one tube, and navigation informa-tion on the other.
Figure 11-66. A typical EFIS system has signal generators for the pilot and copilot sides of the cockpit and a central signal generator that acts as a control in case of disagreement between the other two.
generators. The display controller allows the pilot to select the appropriate system configuration for the current flight situation. [Figure 11-66]
The use of digitally-based microprocessor electron-ics allows several mechanical instruments to be replaced with modern electronic flight instruments displaying the information on one or more cathode ray tubes (CRT's). The signals sent to the various components of the systems are typically linked through a digital data bus. A data bus is made up of a twisted pair of insulated wires surrounded by an outer shielding. The electrical signals sent through the data bus consist of short pulses of voltage on or voltage off (binary ones and zeroes). These pulses are extremely short in duration. A typical system is capable of transmitting signal pulses that are only 10 microseconds in length.
One common bus system is known as ARINC 429.
ARINC stands for Aeronautical Radio Incorporated,
and 429 is a code for a specific digital data standard.
This system uses a 3 2-bit word for all information transmitted over the data bus. The 32-bit word is made up of one parity bit, a sign status matrix, the data, the source destination indicator, and the label or identification of the sending unit. Use of a digital data standard allows computer-processing units to talk to each other. [Figure 11-67]
ELECTRONIC ATTITUDE DIRECTOR INDICATOR (EADI)
The electronic attitude director indicator, like its mechanical predecessor, displays much of the basic flight data needed to maintain a smooth and com-fortable flight. From basic pitch and roll informa-tion to approach decision height, the informainforma-tion is displayed in a color format that is readable even in full sunlight. There are both full-time and part-time displays on most EADIs. The full-time displays give the pilot information needed for flight control. The part time displays offer information typically
Figure 11-67. The ARINC 429 data bus system is one way that digital components can communicate with each other.
needed for runway approach or basic navigation and are only active during the pertinent portion of the flight. [Figure 11-68]
The full-time displays include the aircraft symbol that is used as a reference for pitch and roll infor-mation. To determine the aircraft's attitude the pilot must compare the aircraft symbol to the attitude sphere. The amount of pitch and roll (10, 20,
degrees etc) is indicated on the attitude sphere. The attitude source indicator is also displayed to inform the flight crew which symbol generator is currently driving this EADI.
The part-time displays include:
Rising runway display that appears at 200 feet above ground level and is used during the final portion of an approach.
Figure 11-68. The electronic attitude director indicator (EADI) can display most of the flight attitude information required by the pilot for any given phase of flight.
Figure 11-69. The electronic horizontal situation indicator (EHSI) displays most of the horizontal situation information required by the pilot. The exact data displayed will depend on the mode selected.
• Glide slope and localizer indications that guide the pilot to the touchdown point.
• Marker beacon and radio altimeter displays
shown in the lower left corner of the display.
• Decision height displayed in the lower right
corner.
It should be noted that this EADI is only one of sev-eral versions currently available. The information displayed on any particular system may vary, but the basic configuration of the instrument will remain very similar to that shown.
ELECTRONIC HORIZONTAL SITUATION INDICATOR (EHSI)
The modern electronic horizontal situation indica-tor is modeled after the older electromechanical ver-sion and displays much of the same information. As with the EADI, the EHSI is capable of displaying both full-time and part-time information depending on the current mode of operation. The primary func-tion of an EHSI is to display navigafunc-tional informa-tion. [Figure 11-69]
The electronic horizontal situation indicator can be set for one of four modes of operation. These modes are Plan, Map, VOR, and ILS. The flight crew selects the various modes at the EFIS display controller. In the Plan mode, the CRT displays enroute flight information entered into the flight management sys-tem to provide the flight crew with a visual por-trayal of their recorded flight plan.
In the Map mode, the EHSI will display the cur-rently active flight plan showing waypoints, VORs, airports, etc. A real-time magnetic compass rose and other pertinent navigational information is also displayed on a moving map display. The map changes as the aircraft changes its position during flight. This mode can also display the weather radar if selected. The Map display of the EHSI is most commonly used during enroute portions of the flight.
The VOR and ILS display modes of the EHSI system display the information from the current naviga-tional facility (VOR or ILS). The wind speed, VOR or ILS frequency received, and the current aircraft heading are also displayed.
ELECTRONIC SYSTEMS MONITORING DISPLAYS
In an effort to further reduce instrument panel clut-ter and pilot workload, many of the traditional engine and system instruments have been replaced with electronic monitors. These monitors rely on computers to receive data inputs from the various systems of the aircraft. The computer analyzes the information and transmits a digital signal to one or more CRT displays that inform the flight crew of various systems conditions. The monitoring tems are also used to alert the flight crew of any sys-tem malfunction and, in some case, provide sug-gested corrective actions. [Figure 11-70]
ELECTRONIC CENTRALIZED AIRCRAFT MONITOR (ECAM)
The electronic centralized aircraft monitor system is comprised of two CRT display units, a left and right symbol generator, an ECAM control panel, discrete warning light display unit, two flight warning com-puters and a digital-to-analog data converter. The various components communicate through data bus
Figure 11-70. Electronic systems monitoring displays replace traditional analog gauges with electronic presenta-tions that are easier to read and more reliable.
systems. The left CRT contains information on sys-tems status, warnings and any associated corrective actions. The right CRT displays information in a pictorial format such as control surface positions.
All information displayed on either CRT is shown in a digital format. [Figure 11-71]
Figure 11-71. The electronic centralized aircraft monitor (ECAM) system displays system information to the pilots.
landing. The flight mode information is displayed on the right-hand CRT. The advisory mode information is displayed on the left CRT and contains information of concern to the flight crew, yet not critical.
The failure mode of operation automatically takes precedence over all other modes. The failure mode displays any information that may be considered crit-ical to the flight safety. The left-hand CRT displays appropriate information and corrective action while the right unit displays the status of the failed system.
If a failure occurs, the flight crew is also alerted to the problem through aural and visual warnings.
ENGINE INDICATOR AND CREW ALERTING SYSTEM (EICAS)
This system is used to monitor the engine and vari-ous other systems of the aircraft similar to the
The CRTs of the EICAS system are arranged one on top of the other and a discrete annunciator is located in front of both the pilot and copilot. The standby engine display is a liquid crystal display unit located in the center area of the instrument panel. The liquid crystal display shows the engine performance parameters.
The upper CRT of the system displays primary engine system information in both analog and digi-tal formats. Warnings, cautions and advisories are also displayed on the upper CRT. The lower CRT is normally blank during flight unless the flight crew selects specific information. The lower CRT dis-plays information such as systems status, aircraft configuration, fluid quantities, various tempera-tures and maintenance information.
Figure 11-72. The engine indicator and crew alerting system (EICAS) displays aircraft systems similar to the ECAM. EICAS uses both analog and digital displays.
In the event of one CRT failure, all needed informa-tion is displayed on the operable CRT. In this case, the analog display of information is removed and the system is automatically converted to the com-pact mode. In the event the second CRT fails, the flight crew can still find critical engine information on the liquid crystal display.