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Glossary

Acronyms, part-number conventions, and terms-of-art that come up in avionics docs. Add entries as they come up — every term that confused you on first encounter belongs here.

Instruments and LRUs

  • LRU — Line Replaceable Unit. An avionics box designed to be swapped at the line (i.e., on the ramp) without shop tooling.
  • ADI — Attitude Director Indicator. The artificial horizon with flight-director command bars.
  • HSI — Horizontal Situation Indicator. Heading display with course/glideslope information.
  • RMI — Radio Magnetic Indicator. Compass card with VOR/ADF bearing pointers.
  • ASI — Airspeed Indicator.
  • ALT — Altimeter.
  • VSI — Vertical Speed Indicator.
  • ADF — Automatic Direction Finder.
  • DME — Distance Measuring Equipment.
  • VOR — VHF Omnidirectional Range.
  • XPDR — Transponder.
  • FMC — Flight Management Computer.
  • IRU / IRS — Inertial Reference Unit / System.

Buses and signals

  • ARINC 429 — One-way serial digital bus, 32-bit words, 12.5 kHz or 100 kHz.
  • ARINC 561 — Earlier 6-wire serial standard, used in early INS installations.
  • Synchro — 3-wire AC position-transducer signal (often 26 VAC, 400 Hz reference).
  • Resolver — 4-wire AC position-transducer signal (sin/cos pair).

Electrical

  • 28 VDC — Standard aircraft DC bus voltage.
  • 115 VAC / 400 Hz — Standard aircraft AC bus.
  • 26 VAC / 400 Hz — Reference voltage for synchros and resolvers.

Documents

  • CMM — Component Maintenance Manual. Manufacturer's shop-level service document.
  • IPC — Illustrated Parts Catalog. Aircraft-level parts and assemblies reference.
  • WDM — Wiring Diagram Manual. Aircraft-level wiring reference.