Part-66 Module 5 key terms

A cockpit system that collects aircraft data from sensors and computers and presents it to the crew on electronic displays. It replaces most traditional mechanical gauges and usually includes display units, symbol generators and control panels.

The screen assembly in the cockpit, such as a primary flight display or navigation display, that shows symbols, text and graphics produced by the symbol generator. It contains the display panel and its driving electronics.

A computer that converts aircraft data and pilot selections into the picture drawn on a display unit. It produces the video signals that drive the display and monitors the display for faults.

A coding scheme in which each decimal digit from 0 to 9 is stored as its own four-bit binary group. It is easy to read as hexadecimal but wastes some bit patterns and is less efficient for arithmetic.

A way of representing signed binary numbers in which the most significant bit shows the sign. Negative values are formed by inverting all bits and adding one, allowing subtraction to be done by addition.

A base-16 number system using the digits 0-9 and the letters A-F. Each hexadecimal digit maps directly to four binary bits, so it is used as a compact shorthand when reading or writing binary data.

A circuit that samples a continuously varying voltage and produces a binary number representing its value at that instant. Its key properties are resolution in bits, sampling rate and accuracy.

A circuit that turns a binary number into a proportional voltage or current, so that digital computer outputs can drive analogue devices such as actuators, meters or older instruments.

An extra bit added to a binary word so that the total number of ones is always even, or always odd. The receiver checks this and can detect a single-bit error but cannot locate or correct it.

A widely used civil aircraft digital data bus that sends 32-bit words from one transmitter to up to twenty receivers over a twisted screened pair. It is one-way and self-clocking, with defined labels and transmission rates.

A bidirectional civil aircraft data bus in which many terminals share the same pair of wires and gain access by timing their transmissions. It carries 20-bit words and replaced the one-way ARINC 429 on some aircraft types.

A set of wires, or an optical fibre, carrying digital information between units in a system. The term also describes the internal parallel bus inside a computer that moves data between processor, memory and interfaces.

A basic circuit that performs a Boolean operation on one or more binary inputs to produce a single output, for example AND, OR, NOT, NAND or NOR. Gates are the building blocks of digital circuits.

A table listing every possible combination of inputs to a logic circuit and the output produced for each. It fully describes the behaviour of a gate or combinational circuit and is used to design and check logic.

A digital circuit with two stable states that stores one bit of information until it is changed by a clock or control input. Flip-flops form the registers, counters and memories used in sequential logic.

A single integrated circuit that fetches instructions from memory, decodes them and executes them, performing arithmetic and logical operations on data. It contains a control unit, an arithmetic logic unit and registers.

The part of a processor that performs arithmetic operations such as addition and subtraction, and logical operations such as AND, OR and comparison. Results and status flags are passed back to the processor's registers.

A register inside a processor holding the address of the next instruction to be fetched. It is incremented after each fetch and can be loaded with a new value for jumps and subroutine calls.

The set of connections, usually parallel lines, that carries the address of the memory location or device the processor wants to access. Its width sets the maximum number of directly addressable locations.

Memory whose contents are fixed when it is made or programmed and are normally only read by the processor. It keeps its data when power is removed and holds start-up programs and fixed tables.

A complete electronic circuit, containing many transistors, diodes and resistors, formed on a single piece of semiconductor material and packaged as one component. It can provide anything from simple gates to whole microprocessors.

An integrated circuit in which all the components are fabricated together on one semiconductor chip. This contrasts with hybrid circuits, where separate chips and components are assembled and interconnected inside a single package.

A technique for sending several separate signals over one common medium by giving each signal a share of the capacity, either in time or in frequency. It reduces the number of wires needed between equipment.

A form of multiplexing in which each signal is allotted a short, repeating time slot on a shared link. The receiver separates the signals by recognising their positions within the time frame.

The process of separating a combined signal back into its individual channels at the receiving end, using the time slots or frequencies assigned to each one when the signals were multiplexed.

A thin glass or plastic strand that carries information as pulses of light. The light is confined inside a core by a surrounding cladding of lower refractive index, giving high bandwidth and immunity to electrical interference.

The bouncing of light back into a medium when it strikes a boundary with a less dense medium at an angle greater than the critical angle. This effect keeps light travelling along an optical fibre core.

The loss of signal strength as a signal travels along a cable, an optical fibre or through free space. In fibres it is measured in decibels per kilometre and limits the distance before a receiver or repeater is needed.

A flat display that forms images by applying voltages to a matrix of liquid crystal cells whose light transmission changes. It needs a backlight and is widely used on modern flight deck displays.

A display in which an electron beam is deflected to scan a phosphor-coated screen, producing light where it strikes. It is bulky and uses high voltage, so it has largely been replaced by flat panel displays in aircraft.

A sudden transfer of static charge between two objects at different potentials, for example from a person's hand to a circuit card. It can destroy or degrade semiconductor devices, so protective precautions are required.

A band worn on the wrist and connected by a lead with a series resistor to a known earth point, so that static charge on the body leaks away safely. It prevents damage to electrostatic sensitive devices during handling.

The controlled way of identifying, tracking and recording changes to software and its documentation, so that every approved version can be retrieved and unauthorised alteration is prevented. It forms part of the aircraft configuration control process.

Unwanted electrical energy, either radiated or conducted, that disturbs the correct operation of electronic equipment. Sources include radio transmitters, motors, switching power supplies and nearby wiring carrying changing currents.

The ability of equipment to work correctly in its electromagnetic environment without producing interference that upsets other equipment. It is achieved by filtering, shielding, bonding and careful cable routing.

Strong radio-frequency fields, from sources such as airport or ship radar and broadcast transmitters, that can couple into aircraft wiring and upset or damage electronic systems. Aircraft are tested and protected against specified levels.

Testing facilities built into an aircraft system that automatically check its operation, isolate faults and report the results to the crew or maintenance staff. They may run continuously in flight or only on demand.

A flight control system in which pilot inputs are sent as electrical signals to computers that command hydraulic actuators, replacing mechanical linkages. The computers provide envelope protection and may be backed up by other systems.

Full Authority Digital Engine Control: an engine control system in which a digital computer calculates fuel flow and other settings and commands the engine without a separate mechanical backup, using sensor inputs and built-in test.