Avionics - Typical Electronic / Digital Aircraft System

General electronics/digital aircraft systems are - 

1. ECAM (Electronic Centralized Aircraft Monitoring)
2. EFIS (Electronic Flight Instrument System)
3. EICAS (Engine Indicating & Crew Alerting System)
4. FMS (Flight Management System)     

ECAM (Electronic Centralized Aircraft Monitoring)

• An electronic centralized aircraft monitor (ECAM) is a system, developed by Airbus, that monitors aircraft functions and relays them to the pilots. 
• ECAM produces messages detailing failures and in certain cases, lists procedures to undertake to correct the problem.
• Airbus developed ECAM, such that it not only provided the features of (Engine Indicating and Crew Alerting System)EICAS, but also displayed corrective action to be taken by the pilot, as well as system limitations after the failures.
• Using a color-coded scheme the pilots can instantly assess the situation and decide on the actions to be taken.
• ECAM was designed to ease pilot stress in emergency situations, by designing a paperless cockpit in which all the procedures are instantly available. 

ECAM uses two displays - side by side

• The left hand display is dedicated to inform in checklist format about- 

1. Status of system
2. Warnings
3. Corrective actions

• The right hand display is dedicated to show left hand display information in pictorial or synoptic format.

ECAM Modes

• Flight – phase related:- provides the information about the current phase of aircraft operation (pre-flight, take-off, climb, cruise, descent, approach and after landing)
• Advisory:- mode & status
• Failure Related:- When a failure occurs
• Manual:- permits the selection of diagrams related to any one of 12 systems for routine checking and status messages provided no warnings. 

Block diagram ECAM

Failure Levels

1. Level 3 Failures:red warnings, situations that require immediate crew action and that place the flight in danger.
2. Level 2 Failures:amber cautions, failures that require crew attention but not immediate action
3. Level 1 Failures:Cautions, failures and faults that lead to a loss of system redundancy, they require monitoring but present no hazard. Examples include the loss of DMC(Display Management Computer) when not in use. Level 1 failures are enunciated by a caution (amber) ECAM message only (no aural warning).

EFIS (Electronic Flight Instrument System)

• An electronic flight instrument system (EFIS) is a flight deck instrument display system that displays flight data electronically rather than electro mechanically.

• An EFIS normally consists of a primary flight displa(PFD),multi-function display (MFD), andan engine indicating and crew alerting system (EICAS) display.

• Early EFIS models used cathode ray tube (CRT) displays, but liquid crystal displays (LCD) are now more common. The complex electro mechanical attitude director indicator (ADI) and horizontal situation indicator (HSI) were the first candidates for replacement by EFIS.

• EFIS installation follows the sequence:

            - Displays

            - Controls

            - Data processors

A basic EFIS might have all these facilities in the one unit.

Display Units

The EFIS system provides the crew with two display –

1) Primary Flight Display (PFD)
2) Multifunctional Display (MFD)

      

     PFD is often referred to as the Electronic Attitude Direction Indicator (EADI) and the Navigation Display (ND) as the Electronic Horizontal Situation Indicator (EHSI).

Primary Flight Display (PFD)

• The PFD displays all information critical to flight, including calibrated airspeed, altitude, heading, attitude, vertical speed and yaw.
• The PFD is designed to improve a pilot's situational awareness by integrating this information into a single display instead of six different analog instruments, reducing the amount of time necessary to monitor the instruments.
• PFDs also increase situational awareness by alerting the aircrew to unusual or potentially hazardous conditions. For example, low airspeed, high rate of descent — by changing the color or shape of the display or by providing audio alerts.

Multi-functional Display (MFD)

• The MFD (multi-function display) displays navigational and weather information from multiple systems.
• MFDs are most frequently designed as "chart-centric", where the aircrew can overlay different information over a map or chart.                                Examples of MFD overlay information include the aircraft's current route plan, weather information from either on-board radar or lightning detection sensors or ground-based sensors.
• The MFD can also be used to view other non-overlay type of data (e.g., current route plan) and calculated overlay-type data, e.g., the glide radius of the aircraft, given current location over terrain, winds, and aircraft speed and altitude.
• MFDs can also display information about aircraft systems, such as fuel and electrical systems.

System Layout & Control Panels

The EFIS comprises the following units –

•  Symbol Generator (SG)
•  Display Units *2 (EADI & EHSI)
•  Control Panel
•   Remote light sensor

• EFIS provides pilots with controls that select display range and mode (for example, map or compass rose) and enter data (such as selected heading).

For example, the pilot selects the desired level-off altitude on a control unit. The EFIS repeats this selected altitude on the PFD, and by comparing it with the actual altitude (from the air data computer) generates an altitude error display. This same altitude selection is used by the automatic flight control system to level off, and by the altitude alerting system to provide appropriate warnings.

Advantages of EFIS

The electronic flight instruments have the following advantages –

• Versatile-pilot can select the information
• Display as required, less clutter
• Reduce pilot’s workload
• A degree of redundancy is available even with the simple two-screen EFIS installation. Should the PFD fail, transfer switching re positions its vital information to the screen normally occupied by the navigation display.

EICAS(Engine Indicating & Crew Alerting System)

• Engine-indicating and crew-alerting system (EICAS)  is an integrated system used in modern aircraft to provide aircraft crew with aircraft engines and other systems instrumentation and crew annunciations.
• The basic system comprises two display units, a control panel, and two computers supplied with analog and digital signals from engine and system sensors.
• The system provides the flight crew with information on engine parameters and warning / caution / advisory alert messages (as required).

Display Units

• The units are mounted one above the other, the upper unit displaying the primary engine parameters and warning and caution messages.
• The lower unit displays secondary engine parameters (fuel flow, oil quantity, pressure and temperature, and engine vibration), status of non-engine systems, aircraft configuration and maintenance data.
• In the normal mode in flight, only the primary engine parameters are displayed; the lower display unit screen remaining blank.
• Warning, caution and advisory messages are displayed in red and yellow on the left-hand side of the upper display unit screen as conditions dictate. Abnormal secondary engine parameters are automatically displayed on the lower display unit.

FMS (Flight Management System)

• A flight management system (FMS) is a fundamental component of a modern airliner's avionics.
• FMS is a specialized computer system that automates a wide variety of in-flight tasks, reducing the workload on the flight crew to the point that modern civilian aircraft no longer carry flight engineers or navigators.
• A primary function of FMS is in-flight management of the flight plan. Using various sensors (such as GPS and INS often backed up by radio navigation) to determine the aircraft's position, the FMS can guide the aircraft along the flight plan.
• The FMS is normally controlled through a Control Display Unit (CDU) which incorporates a small screen and keyboard or touch screen. 

FMS Operations

1.   Compares the pilot selected flight plan with the actual horizontal and vertical aircraft position.
2.   In case of difference between them, the FMS makes a steering and thrust command. 

•   The pilot sets the flight plan through the MCDU.
•   A database with airports, runways, way points is used.
•   FMS automatically selects optimal parameters e.g. climb ration, optimal speed etc.
•   Shows information about the flight plan on MCDU.
•   Exchanges information and commands the Autopilot / Auto throttle Flight System AFS.
•   Gives information to the EFIS displays. 

FMS Description 

}Navigation:

}FMS uses information from its database to automatically tune the navigates (ILS, VOR, DME).

}Database must be updated every 28 days.

}Performance:

}The FMS calculates the shortest possible flying time at the lowest fuel consumption. Can give predictions of fuel quantities and arrival times at future points in the flight plan.

}Guidance:

}The FMS compares the desired position of the aircraft according to the flight plan, with the actual aircraft position. If there is a difference, FMS commands the AFS to bring the aircraft to the desired position.

}Position and velocity are calculated using the IRS, GPS, VOR and DME.

}EFIS Display:

}FMS is the primary source of information displayed on EFIS.