B1-05.15 TYPICAL ELECTRONIC DIGITAL AIRCRAFT SYSTEMS 1

• Today's complex aircraft require design engineers to prioritize system troubleshooting capabilities as equally important as repair or inspection.
• Self-contained diagnostics are crucial because troubleshooting complex digital system would be nearly impossible without them.
• These diagnostics used for electronic/avionics systems troubleshooting are known as BITE (Built-In test Equipment).
• There are several versions of built-in test equipment in use today.

Simple BITE Systems

• Incorporate a go/no-go red or green LED on the LRU.

Complex BITE systems

• Utilize a multi-character display, monitor multiple LRUs, and can test associated wiring.

Current Generation BITE

• Self-diagnostics equipment using centralized monitoring systems with flight deck displays to activate tests.
• Faults from several BITE systems are monitored in one place.
• These include paper printouts and data transmission to the maintenance facility during flight

Boeing's Advanced Troubleshooting System

• Known as CMCS (Central Maintenance Computer System).

Airbus' Advanced Diagnostic System

• Called CFDS (Centralized Fault Display System).

Advanced Systems

• Feature enhanced BITE to aid in troubleshooting and are more accessible than older systems.
• A commercial airliner may have multiple BITE units monitoring different systems, each receiving input from individual system components being tested.
• Simple BITE systems contained within the LRU being monitored were accessed in the avionics equipment bay or similar area.

BITE Philosophy

• Most aircraft systems consist of Line Replaceable Units (LRUs) like black boxes, sensors, actuators, or probes.
• Most LRUs are controlled by digital computers and are permanently monitored for safety reasons.
• A section of the computer is dedicated to these functions, known as the BITE section.

BITE Operation

• During normal operation, BITE continuously monitors internal LRU circuits, inputs, outputs, and links between system LRUs.
• When a failure occurs, BITE identifies the failed LRU, determines if the failure is intermittent or permanent, captures a snapshot of the system environment, and stores the data in non-volatile memory.

BITE Function

• Information is sent to a centralized maintenance device.
• BITE tests can be initiated via the centralized maintenance device, resulting in advantages such as easy fault identification, shorter troubleshooting, simplified documentation, and standardized equipment.
• BITE can be divided into 4 groups.

Types of BITE Tests

• Power Up Test: First safety test to ensure compliance with safety objectives. Performed on the ground after a power cut exceeding 200 milliseconds. In air, limited to quick-return items, including microprocessor, memory, data line, and configuration tests.
• Cyclic Tests: Also known as In Operation Tests, performed continuously without system disturbance. Includes watchdog tests(restarts microprocessor), RAM tests and data line (ARINC 429) message validity.
• System Test: Used to test the system for troubleshooting or after system restoration following LRU replacement to check integrity.
• Specific Tests: Generates stimuli to command devices. For example, actuators or valves that can have a major effect on the aircraft, like slat movement or engine dry cranking,

BITE Benefits

• Reduces aircraft maintenance downtime and monitors the system after repairs.

Maintenance Control Display Unit(MCDU)

• Contains data screen, keyboard, function keys, mode keys, and line keys to send commands to connected systems like FM, ACMS, CMS, SAT and ATSU.
• The MCDU is used by a series of keystrokes to review a specific system status or preform test.
• The MCDU displays the STATUS PAGE when powered up.
• MAINTENANCE MENU will be displayed when the line key next to <CMS is selected.
• By selecting the key next to <SYSTEM REPORT/TEST, the SYSTEM REPORT/TEST pages will be displaye
• By using scroll keys, the specific desired system can be found.

Simple BITE Circuits

• Incorporated in many aircraft systems built in the 1980's or later.
• Independent systems, such as the radio altimeter, often contained BITE circuitry in the main LRU.
• It runs the radio altimeter BITE by providing power, pressing the TEST button, and monitoring the LEDs and display. The BITE circuit tests the transceiver, the antenna, and the radio altimeter display.

Self-Test BITE

• Initiated from a switch on the flight deck.
• For example, the Ground Proximity Warning System (GPWS).
• It test the GPWS computer and interfacing system validity using a test button on the panel during the test.

Successful GPWS test events sequence

• The pilots BELOW G/S light will illuminate and remain illuminated for as long as test button is pressed and held.
• The GLIDESLOPE aural will sound once only, followed by the WHOOP – WHOOP – PULL UP aural, at reduced volume and repeating approximately 2 to 8 times, provided the TEST button remains pressed and held.
• When the WHOOP – WHOOP – PULL UP aural is sounding, the pilots PULL UP light will be illuminated.
• If the TEST button is released after the WHOOP – WHOOP – PULL UP has sounded once (at least) the aural will sound again at full volume.

ACARS (Aircraft Communications Addressing and Reporting System) Introduction

• ACARS is a radio teletype mode developed in the early eighties as an addressable, digital data link for commercial and business aircraft. It was produced to reduce workload by using computers to exchange many routine reports and messages.
• Onboard maintenance systems transmit information to a ground station, including aircraft system faults and performance data, to reduce dispatch delays.
• Maintenance can remotely review and diagnose to schedule repair. This provides for a faster turnaround.

ACARS Components

• Key parts are the Management Unit (MU), Control Unit (CU), and a printer.
• MU formats all flight data collected from Control/Event sensors, with a GMT clock signal.
• The MU also controls data transmissions via and receives via VHF.
• The CU contains an alphanumeric board and serves as the flight crew interface.

ACARS Built In Test Equipment

• The ACARS MU and related subsystems are monitored by a circuit within the MU. This circuit reports failures to the central maintenance computer and monitors ACARS components.
• The MU test switch initiates ACARS test-during test, all lights illuminate for 3 seconds. Then all lamps extinguish for 3 seconds, then the appropriate lamp should remain illuminated. Green means OK, red means a systems failure.

Data Bus Fundamentals

• Digitally based microprocessor allows mechanical instruments to be replaced with electronic flight instruments on Multi-Function Displays (MFDs).
• Signals are linked via the digital data bus and transmitted to symbol generators digitally from sensors (ARINC 429 629) or Bus controller (MIL-STD 1553).

Airbus' Electronic Centralised Aircraft Monitoring (ECAM)

• ECAM system displays information from major systems on two display units. This provides system status, warnings, and failure indications.
• Maintenance staff can view system status, synoptic diagrams, and failure memory.
• ECAM displays are in the centre of the instrument panel.
• In latest data bus aircraft, the display can be in front of pilot positions if selected.

ECAM Displays

• ECAM operates by displaying color-coded warnings, cautions as well as system status.
• The upper screen provides primary engine data, system info as well as warnings from other systems.
• The lower screen displays secondary engine data, aircraft status, and system detail.

ECAM System Operation

• Main component is the Flight Warning Computer (FWC).
• The FWC receives inputs from aircraft systems signals pass through the Signal Analogue-Digital Converter for analogue based input.
• FWCs monitor each other for errors, and output is sent to ECAM symbol generators, which is then input to ECAM displays.
• Under normal conditions the FWC provides output to only one symbology generator.
• Symbol generators are built into the display in later models

Electronic Flight Instrument System (EFIS) Purpose

• Primarily to give the flight crew the information required to operate the aircraft.

EFIS Components

• Four interchangeable Cathode Ray Tubes(CRT displays, two per-pilot with 3 symbol generators plus 2 control panels and source panels.
• Center symbol generator switches drive signal should either captains or first officers primary symbol generator fail.

EFIS operation

• Symbol generators provide interface between and between the aircraft's navigation, sensor systems, display units and control and control panel.

• Creates drive signals to produce symbology, power control in system monitoring.

• Display controller provides switches and button so the pilot can select info sources that he/she wishes to be the relevant phase of flight.

• EFIS display can be seen on whichever display is selected in-front of the pilot.

Primary Flight Display (PFD_

• Combines information given by and EADI and EHSI.
• The PFD displays such data as attitude, compass, flight control and primary air stats.
• Receives data from analogue-digital converters for non digital equipment or, other avionic systems, like Traffic Alert Collision Avoidance System.

Multifunction or Navigation Display (MFD or ND)

• Displays such information as compass, radar, flight management and even information on diagnostic. Also provides backup for the PFD.
• The MFD receives he same data as the PFD as well as data for such areas as weather radar

Boing's Engine Indicating and Crew Alerting System (EICAS).

• EICAS displays aircraft systems data through CRT or LCD.
• First appeared on the 757 and 767 aircraft.

EICAS Information

• Engine and system data is central to the flight data.
• The primary engine data is always on the display, but on the even of a failure if the flight engineers attention is drawn by an automatic display message showing the problem.
• Systems can display values if required and are selected by the crew though a control pilot of the system.
• Works as a complete system to monitor all aircraft systems by using the Central Maintenance Computer.

EICAS - ACARS connection

• EICAS is able to transmit data through the ACARS system to the ground station.

EICAS Upper Primary Display

• Normally shows primary engine indications, crew alert system, fuel quantity and environmental control data.

EICAS Lower Display

• Has auxiliary EICAS formats and it the normal display. During normal flight the lower EICAS is blank so, the pilots can select the lower screen if more information is needed.

EICAS Control Panel

• This panel give control to the EICAS functions and to select what will be displayed.

EICAS Component Diagram

• The diagrams shows such thing as where information is found on the EICAS or computer in the aircraft.

EICAS Operation

• When only one computer is running what happens to prevent a failure. This provides an improved level of maintenance data for the ground crew.

EICAS BITE Test

• The test in the EICAS will perform testing of the EICAS computer upper as lower master unit including the test switch.

Fly-By-Wire Flight Control System

• Uses digital computers with complete control over all the flight control surfaces.

• When wanting to change aircraft attitude, the movement for the side controller are processed by computers.

• The electrical current sent to the operating electrical actuators change the plane/space as directed.

• The software programmed decides if it is going to perform the measure, for example the selecting of the spoiler to perform speed change.

Flight Management System (FMS)

• Its is an interface that many areas of the air craft aids in the primary functions.
• The FMS provides air ground state, radio and other data
• The FMS us centered around a computer called the FMC the FMS is design to reduce the crew load with planning while maintaining air speed.
• The FMS takes the function of inertial navigation, fuel control, air data and data from the EICAS computer

Flight management System (FMS) - FMC Operation

• There may be one or more FMC computer installed in the aircraft. To action the data independently. This provides the system required redundancy should one FMC fail.

FMS Control Display Unit

• The CDU allows access to fault data. It allows started systems tests and the screen can be printed by using on board printers.
• In the MCDU, the maintenance pages show maintenance data that is accessible on the ground

FMS Built In Test Equipment

• The FMS continuous to run itself by being controlled by the BITE software programmed into the (FMC. The bite continuous to happen every time the FMC is powered.
• The testing is controlled by the maintenance system of the aircraft.
• In some systems there red(Fail) light that will illuminate if the time of test the FMC fails at any time.
• All systems should be working while the process starts.

GPSS - Global Position System

• Satellites now allow aircraft including ships to know when the GPS is to perform fast location to any site.
• Components GPS are the aircraft GPS are the antenna and control screen.
• The system then processed the information to update inertial.

IRS - Inertia Reference System

• Provides the data and navigation needed for the aircraft depending if the unit is at total auto flight system.
• Gyros and accelerometers are used to track altitude as well as position along the flight path.

IRU Components

• Every aircraft has there own IRU. So that the function still run along with the operations of the aircraft. Including an ISDU one for the crew.
• When in the IRU there a battery that helps with power.
• Once it power and tested, the IRU passes and this the pilot knows because the system goes in to initialization.

Traffic Alert and Collision Avoidance

• The goal of this system is to provide guidance so pilots know of other airborne. To avoid probable collusion.
• The traffic alert and collision avoidance system functions outside if any ground installation.
• The TCAS is always monitoring and evaluating when airborne to give the safest flight crew as possible.