Module 5.1 and 5.11 Electronic instrument systems and electronic displays

Module 5 (Digital techniques / electronic instrument systems) is 20 questions for A and B3, 40 for B1 and 72 for B2/B2L under EASA. These two sub-modules are examined for every category.

Knowledge levels

Sub-module	A	B3	B1	B2 / B2L
5.1 Electronic instrument systems	1	1	1	1
5.11 Electronic displays	1	1	2	2

From the "basic T" to the glass cockpit

• Classic instruments were arranged in the basic T: airspeed (left), attitude (centre top), altimeter (right), heading/HSI (centre bottom).
• Electronic instrument systems keep this logic on screens. A typical modern layout has, for each pilot, a primary flight display (PFD) and a navigation display (ND); in the centre, engine and system displays (EICAS or ECAM); plus a standby instrument (often an integrated electronic standby).
• Displays are driven by display management/symbol generator computers that receive data from air data computers, inertial/AHRS units, navigation receivers and engine sensors over data buses.

System	What it shows	Typical manufacturer use
EFIS (electronic flight instrument system)	PFD: attitude, speed tape, altitude tape, vertical speed, heading, flight-mode annunciations, flight director; ND: map, route, weather radar, TCAS, compass rose	all glass cockpits
EICAS (engine indication and crew alerting system)	primary engine parameters, crew alerts (warnings, cautions, advisories), system synoptic pages	Boeing and others
ECAM (electronic centralised aircraft monitoring)	upper display: engine and warning messages; lower display: system pages and checklists/actions	Airbus

Key fact: The PFD and ND form the EFIS for each pilot; EICAS (Boeing) or ECAM (Airbus) shows engines and system alerts on the centre displays.

Redundancy and reversion

• If a display fails, its format can be transferred to another screen (reversionary modes), e.g. the PFD moves to the ND position, or the engine display to a lower screen.
• Source-select switches allow the captain's display to use the first officer's air data or inertial source.
• Alert hierarchy: warning (red, immediate action), caution (amber, timely awareness), advisory (lower priority, often amber/white/cyan).

Display technologies (5.11)

Cathode ray tube (CRT)

• An electron gun (heated cathode, control grid, accelerating anodes) produces an electron beam focused on a phosphor-coated screen, which glows where hit.
• Deflection by electrostatic plates or magnetic coils. Colour CRTs use three guns (red, green, blue) and a shadow mask.
• Drawbacks: heavy, bulky, high voltage (several kV), heat, poor sunlight readability. Found in older EFIS/EICAS installations.

Light-emitting diode (LED)

• Semiconductor junction that emits light when forward biased; colour set by the semiconductor material.
• Used for indicator lights, segment displays, and as back-lighting for LCDs. Very reliable and long-life.

Liquid crystal display (LCD)

• Liquid crystal molecules between two polarising filters twist the polarisation of light; an applied voltage untwists them and blocks or passes light.
• LCDs do not emit light: they need back-lighting (fluorescent or, now, LED).
• Active-matrix LCD (AMLCD) has a thin-film transistor (TFT) at each pixel - fast, high contrast, full colour. Standard in modern cockpits.
• Advantages over CRT: thin, light, low power, low heat, good readability. Limitations: narrower viewing angle (on older types), slow response at very low temperature.

Feature	CRT	LCD (AMLCD)	LED
Emits own light	yes	no (needs back-light)	yes
Weight / depth	heavy, deep	light, thin	light
Power / heat	high	low	low
Typical use	older EFIS	modern EFIS, MFDs	annunciators, back-lights

Other display terms

• Pixel: smallest controllable picture element. Resolution: number of pixels.
• Brightness control: manual knobs plus automatic dimming via ambient-light (photo) sensors.
• Head-up display (HUD): projects symbology onto a transparent combiner in the pilot's line of sight.

Maintenance considerations

• Display units are LRUs; most faults are cleared by BITE-guided replacement.
• Screens must be cleaned only with approved materials (anti-glare coatings scratch easily).
• Many display units contain ESD-sensitive devices.
• Software/database loads must match the approved configuration (see 5.13 Software management).

Exam tips

• LCDs need back-lighting; CRTs and LEDs emit light.
• ECAM = Airbus; EICAS = Boeing (and many others).
• PFD shows attitude and air data; ND shows navigation, weather and traffic.