Module 5.15 Typical electronic/digital aircraft systems

Knowledge level

Sub-module	A	B3	B1	B2 / B2L
5.15 Typical electronic/digital aircraft systems	1	1	1	1

Level 1 for everyone: know what each system does, its general arrangement and its BITE. Detailed operation follows in Modules 11, 12 and 13.

Built-in test equipment (BITE)

• Self-test circuits and software inside an LRU that check its own operation and its inputs/outputs.
• Power-up BITE runs when the unit is switched on; continuous BITE monitors during operation; initiated (interactive) BITE is started by a technician from a control panel or maintenance computer.
• Results are stored as fault codes and reported to the central maintenance computer/onboard maintenance system (CMC/OMS) - allows quick fault isolation to the faulty LRU.

The systems named in the syllabus

Acronym	System	Function
ACARS	ARINC Communication Addressing and Reporting System	digital datalink between aircraft and ground (airline operations, ATC clearances, engine/maintenance reports) via VHF, HF or satcom
FBW	fly-by-wire	pilot inputs are converted to electrical signals; flight control computers command the actuators, often with flight envelope protection
FMS	flight management system	computes lateral and vertical navigation, performance and fuel; holds the navigation database; outputs to autopilot and autothrottle; crew interface through the MCDU
IRS	inertial reference system	gyros (ring-laser or fibre-optic) and accelerometers give attitude, heading, position and velocity without external signals; needs alignment on the ground
ECAM	electronic centralised aircraft monitoring	Airbus engine/system display and alerting with action lists
EICAS	engine indication and crew alerting system	engine display and crew alert messages (Boeing and others)
EFIS	electronic flight instrument system	PFD and ND for each pilot
GNSS	global navigation satellite system	GPS, Galileo, GLONASS, BeiDou; position and time from satellites; augmentation by SBAS (EGNOS/WAAS) and GBAS
TCAS	traffic alert and collision avoidance system	interrogates other aircraft transponders, shows traffic, issues traffic advisories (TA) and resolution advisories (RA) (TCAS II)
IMA	integrated modular avionics	shared computing modules host several functions (partitioned) instead of many dedicated LRUs
Cabin systems	cabin intercommunication data system, in-flight entertainment, passenger connectivity
Information systems	electronic flight bag, onboard network servers, electronic logbook, maintenance documentation

Key fact: TCAS needs the transponder of the other aircraft to work: it cannot see aircraft without a working transponder. RAs give vertical guidance only (climb/descend).