Glossary
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AOG: Abbreviation for Aircraft On (the) Ground.
ARINC: Abbreviation for Aeronautical Radio, Inc. ARINC supports the aviation industry by providing communications and information processing services; systems engineering, development and integration; as well as guidance for establishing avionics and other technical standards for global air transportation.
ARINC Level 1 Cooling: Pressure drop of 5mm + 3mm of water at the LRU design flow rate from inlet to exhaust.
ARINC Level 2 Cooling: Pressure drop of 25mm + 5mm of water at the LRU design flow rate from inlet to exhaust.
Attenuation: The decrease of power or signal as it travels through a cable. Normally presented in db per 100 feet in length.
ATR: Abbreviation for Austin Trumbull Radio. ATR is the standard unit of measurement used for determining the box width of line replaceable units (LRUs) as defined in the ARINC 404 specification. ATR box sizes are expressed as a fraction of a basic 1 ATR width (e.g. 1/4 ATR, 3/8 ATR, 1/2 ATR, etc.).
Bend Radius: The radius of curvature that a fiber optic or metallic cable can bend without causing damage.
Braid: A fibrous or metallic group of filaments interwoven in tubular form to create a covering over one or more wires. Can be flattened to form a strip or ribbon.
Capacitance: The ability to store electrically separate charges between two conductors having different potentials.
Coaxial Cable: Known as Coax, a cable consisting of two cylindrical conductors with a common axis, separated by a dielectric.
Connector Cutout: The opening in the connector plate of a tray assembly for mounting the LRU mating connector (see diagrams on ARINC 404 Tray Design Features and ARINC 600 Tray Design Features).
Connector Plate: The vertical plate towards the back end of a tray for mounting the LRU mating connector (see diagrams on ARINC 404 Connector Plates and ARINC 600 Connector Plates).
DC Resistance: In DC (direct current) circuits, the opposition a material offers to current, measured in ohms.
Deformation: The stamped impression in a tray that adds strength and rigidity, and enables increased air flow for LRU cooling.
Dielectric: Any insulating material between two conductors which allows electrostatic attraction and repulsion to take place across it.
Dielectric Stiffener: An insulating material used to prevent center conductor distortion during the insertion of the center contact into the connector body.
DME: Abbreviation for Distance Measuring Equipment.
EFB: Abbreviation for Electronic Flight Bag System.
EMI: Abbreviation for Electromagnetic Interference. EMI refers to the electric and magnetic fields generated by electron motion through conductors that cause interference in a system's environment.
FAR: Abbreviation for Federal Aviation Regulation.
Flat Bottom: Utilized when tray must be mounted on a flat surface and tray-mounted forced cooling is not necessary. When using flat bottom trays, make sure that the hold downs can be positioned off the edge of the shelf to ensure a flat surface mount (tray hold downs protrude below the tray bottom).
Ferrule: A short tube used to make solderless connections to shielded or coaxial cable.
Front Hold Down: The mechanical device used in securing the front of the LRU to a mounting tray. (See Hold Down Guidelines, ARINC 404 Hold Down Guide and ARINC 600 Hold Down Guide).
GPRS: Abbreviation for General Packet Radio Service. GPRS refers to a standard for wireless communications which run at speeds up to 115 kilobits per second.
GPS: Abbreviation for Global Positioning System.
GSM: Global Systems for Mobile communications, a standard for wireless communications which runs at speeds up to 9.6 kilobits per second.
HF: Abbreviation for High Frequency.
IFEC: Abbreviation for Inflight Entertainment Center.
Impedance: The total opposition a circuit or cable offers to the flow of alternating current at a particular frequency. Impedance combines resistance and reactance and is measured in ohms.
Inflight Mobile Telephony: The ability for airlines to offer their passengers the use of portable voice and data communication devices such as mobile phones, smartphones, laptop computers, and Personal Digital Assistants (PDAs), as well as in-seat equipment through GSM / GPRS onboard and other high-speed satellite broadband communication systems.
INS: Abbreviation for Inertial Navigation System.
Insertion/Extraction: The type of front hold down with a built-in clutch to protect against over-tightening. This hold down also includes an extracting function to remove the LRU from the tray. (See Hold Down Guidelines, ARINC 404 Hold Down Guide and ARINC 600 Hold Down Guide).
Insertion Loss: Measure of the attenuation of a device through the determination of the output of the system before and after the device is inserted.
Jacket: An outer covering of a cable, usually nonmetallic, used for protection against environmental hazards.
LED: Abbreviation for Light Emitting Diode.
Long/Long: Size designation for LRU mounting trays. Designation indicates a Long LRU placed in a Long tray (see ARINC 404 Size Configurations).
Loss: The portion of energy applied to a system that is dissipated and not used.
LRU: Abbreviation for Line Replaceable Unit. LRUs are the modularized avionics systems equipment units (black boxes) that support communication, navigation, auto flight, in-flight entertainment or other systems.
LRU Width: The dimension for modularized avionics systems equipment designated as ATR in the ARINC 404 standards and MCU in the ARINC 600 standards (see pages ARINC 404 Size Configurations and ARINC 600 Size Configurations).
MCU: Abbreviation for Modular Concept Unit. MCU is the standard unit of measurement used for determining the box width of Line Replaceable Units (LRUs) as defined in the ARINC 600 specification. MCU box sizes are designated in multiples of 1 unit or 1 MCU (e.g. 2 MCU, 3 MCU, 4 MCU, etc.).
Metering Plate: An aluminum alloy plate designed with multiple holes and placed in the deformation of a mounting tray to enable cooling air to flow through the LRU. The holes can be sealed off with Metering Plugs to regulate the amount of cooling airflow to the LRU.
Metering Plugs: Inserts that fit into metering plate holes to regulate air flow (see ARINC 404 Metering Plates and ARINC 600 Metering Plates).
MIL Spec: Abbreviation for Military specifications, the demand imposed on a system to meet military operational needs.
MLS: Abbreviation for Microwave Landing System.
MTBF: Abbreviation for Meantime Between Failure.
Negative Pressure Cooling: Cooling air that is directed through the top of an LRU and exhausts at the bottom of the equipment.
Oval Cutout: Opening added to a flat bottom tray to allow air flow for convection cooling of LRU. ECS cutouts can be customized to any shape or size as required.
Plenum: An enclosure (duct) placed on the bottom of mounting trays where cooling air is channeled before flowing up through the LRU (see ARINC 600 Fan Cooled Trays). In less common applications, air is exhausted through the plenum after cooling air is channeled downward through the LRU (see negative pressure cooling).
Phase Matching: Process of ensuring that the number of electrical degrees is within the limits of manufacturing specifications.
PMA: Abbreviation for Parts Manufacturer Approval.
Positive Pressure Cooling: Cooling air that is channeled through the bottom of an LRU and exhausts at the top of the equipment. The two methods that are generally used for positive pressure cooling are: aircraft supplied and fan supplied forced airflow.
Rack: Support structure, usually installed in the avionics bay, which secures one or more equipment shelves (see Integrated Racks & Shelf Assemblies).
Rear Alignment Pins: A solid or spring loaded pin used to align and secure the rear of an LRU box to the connector plate. (See ARINC 404 Hold Down Guide).
Resistance: In DC circuits, the opposition a material offers to current flow, measured in ohms. In AC circuits, resistance is the real component of impedance, and may be higher than the value measured at DC.
RF: Abbreviation for Radio Frequency.
RFI: Abbreviation for Radio Frequency Interference.
RTCA: Abbreviation for Radio Technical Commission for Aeronautics.
SATCOM: Abbreviation for Satellite Communications System.
Shelf: A support structure located in the avionics bay for securing mounting trays onto the aircraft.
Shield: A tape or braided metallic layer placed around a conductor or group of conductors to prevent electrostatic interference between the enclosed wire and the external fields.
Short/Long: Size designation for LRU mounting trays. Designation indicates a Short LRU placed in a Long tray (see ARINC 404 Size Configurations and ARINC 600 Size Configurations).
Short/Short: Size designation for LRU mounting trays. Designation indicates a Short LRU placed in a Short tray (see ARINC 404 Size Configurations and ARINC 600 Size Configurations).
SKYDROL®: A line of hydraulic fluids used in aircraft manufacturing for its fire resistant properties. SKYDROL is a product Solutia Inc.
Standing Wave Ratio: The ratio between maximum and minimum current or voltage along a line.
STC: Abbreviation for Supplemental Type Certificate.
TCAS: Abbreviation for Traffic Alert Collision Avoidance System.
TEFLON®: A DuPont company trademark for polytetrafluorethylene.
TFTS: Abbreviation for Terrestrial Flight Telephone System.
Thumbscrew: A self-locking ratchet style front hold down normally used for ARINC 404 equipment (See ARINC 404 Hold Down Guide and ARINC 600 Hold Down Guide).
Tray: The mounting structure used to secure the LRU in place, protect it from movement and electronically connect it to the aircraft system. The basic tray normally consists of the tray shell, front hold downs, connector plate and ARINC connector. The tray is mounted on an equipment shelf which is located on the aircraft.
Tray Bottom: Part of the tray that supports the LRU. The standard ARINC 600 tray bottom has a stamped deformation with metering plate and metering plugs. The standard bottom for an ARINC 404 tray is flat with a cutout for convection airflow (see diagrams on ARINC 404 Tray Design Features and ARINC 600 Tray Design Features).
Tray Length: The overall dimension of the tray, which is measured from the front of the tray shell (excluding hold downs) to the back of the tray shell.
Tray Mounting: Refers to the different types of methods used to mount the equipment trays onto the aircraft. Methods include shock and vibration isolation, mounting rails, shelf mounting and baseplate mounting. Because tray mounting is an important consideration not specified in ARINC 404 or 600 specifications, contact ECS Customer Service for more information.
Tray Shell: The basic aluminum structure of the LRU mounting tray minus the hold downs, connector plate and ARINC connector.
Velocity of Propagation: The transmission speed of an electrical signal moving down a length of cable compared to its speed in free space. Normally expressed as a percentage.
VCC: Abbreviation for Video Control Center.
VHF: Abbreviation for Very High Frequency.
VOR/LOC: Abbreviation for Visual Omni Range/Localizer.
VSWR: Abbreviation for Voltage Standing Wave Ratio (see standing wave ratio).
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