Avionics Systems and Software
part 1
Avionics Systems and Software
* AVIONICS : An Embedded System
* Avionics-Functionality
* Major Components of Avionics Systems
* Avionics Architecture
* Avionics Mission Functions
AVIONICS : An Embedded System
Avionics is an embedded part of a larger System-Flight System- comprising
* Aircraft
* Pilot/s
* Atmosphere
* Environment
** Air Traffic and Guidance Control
** External Sensors, Satellites,etc
** Enemy targets
AVIONICS : An Embedded System
Relationships with various parts
* Aircraft : Avionics is a part of the aircraft
* Pilot/s :
Interact with Avionics Systems
* Atmosphere : Avionics measures atmospheric
parameters
* Environment : Transmits and receives data and
voice, releases weapons,etc
Role Of Avionics Systems
In a modern aircraft, Avionics enables a pilot to :
* Fly the aircraft (vehicle control or flight control system)
* Perform the operational role of the aircraft
** Transportation of passengers safely from one
place to another ( Commercial aircraft)
** perform various mission functions
*** Navigation
*** Release of missiles/bombs
Avionics- an embedded system
* Receives inputs
* Computes
* Generates outputs
Avionics- an embedded system
Receives inputs from :
* Rest of the aircraft : aircraft fuel, electrical,hydraulic
weapons status, etc
* Pilot/s : controls and switches
* Atmosphere : air data
* Environment : through data links, voice from ATC,etc
Avionics-an embedded system
* Computes required parameters for navigation and fire
control :
** Navigation algorithms:Guidance to steer point,
desired track ,etc
** Fire Control algorithms: weapon aiming,missile
launch,etc
Avionics-an embedded system
* Outputs computed results to :
** Displays:
*** Basic flight , steering and navigation
parameters
*** Weapon aiming, missile launch symbologies
*** Sensor outputs
*** Failures and warnings
Avionics-an embedded system
* Outputs computed results to :( continued)
** Audio System: Avionics status and warnings
** Weapons
* Outputs control weapon launch and firing
* Outputs control/coordinate/manage sensors
optimally
Avionics-Functionality
As an embedded system, Avionics must perform the following
major functions :
*
Basic Flight and Steering
*
Navigation guidance including inertial , radio and
satellite navigation
** Inertial navigation Systems (INS)
** Radio Navigation Aids (TACAN, VOR)
** Satellite Navigation (GPS)
** Hybrid INS + GPS
Avionics-Functionality(continued)
*
Communications : voice and data
** HF, VHF, UHF
*
Identification : Friend or Foe
** IFF
*
Landing Aids : ILS (Instrument Landing System)
*
Passenger Entertainment
*
Autopilot
Avionics-Functionality(continued)
*
System Crew dialogue
** Cockpit Controls and inputs management
** Multifunction Displays
** Symbology Generation
** Display management
** Warnings management
*
Failure management and reconfiguration
Avionics-Functionality(continued)
*
Integrated Maintenance
** In Flight
** On Ground Supplementary
*
Electronics warfare: ECM, ECCM
*
Sensors :
** Electromagnetic Radars : Fire Control,
Weather, Terrain following /avoidance
** FLIR:Forward Looking Infrared Radar
Avionics-Functionality(continued)
*
Sensors ( continued):
** LDP : Laser Designation Pods
** Air Data
** Radio Altimeter
** Collision avoidance ( TCAS)
*
Operational Data Insertion and Retrieval
*
Flight Control System (for Fly by Wire Aircraft)
Avionics-Functionality(continued)
*
Flight Control System (for Fly by Wire Aircraft)
*
Fire Control algorithms : Air to Air, Air to Ground,
Air to Sea
*
Weapon Release Systems : Missiles, Smart and dumb
bombs, Guns
** Weapon selection and prepartion
** Launch/fire sequencing
Major Components of Avionics Systems
* Cockpit Area
**
Pilot’s stick or Control column and switches
on it
**
Throttle and switches on it
**
Switches of all kinds on side console and
Instrument panel,etc
**
Up Front control Panel( on fighters only)
and small LCD display
Flight Instruments: Multi Function Displays
Major Components of Avionics
Systems(continued)
* Cockpit Area
**
Flight Management or Navigation
control panel and small LCD display
**
Many Conventional Flight Instruments:
*** Pressure Altimeter
*** Rate of Climb Indicator(ROCI)
or Vertical Speed Indicator(VSI)
*** Artificial Horizon( gyroscopic)
MULTIFUNCTION PROCESSOR UNIT (MPU):
The multifunction processor unit provides sensor input processing and switching and the
necessary deflection and video signals for the multifunction display. The MPU can
provide the deflection and video signals to the PFD and ND displays in the event of
failures to either or both display processor units.
Major Components of Avionics
Systems(continued)
* Cockpit Area
**Conventional Flight Instruments(continued):
*** Pressure Altimeter
*** Rate of Climb Indicator(ROCI)
or Vertical Speed Indicator(VSI)
*** Artificial Horizon( gyroscopic)
*** Air Speed Indicator (ASI)
*** Angle of Attack Indicator
Major Components of Avionics
Systems(continued)
* Cockpit Area
**Conventional Flight Instruments(continued):
*** Various temperature gauges
*** Various Engine/s gauges
*** Central Warning Panel
*** Magnetic Compass
*** Gyro Compass
Major Components of Avionics
Systems(continued)
* Cockpit Area
** Electronic Display Systems
*** Heads Up Display ( HUD)--Fighters only
Symbology is displayed to the pilot on a
transparent glass screen in front of him.
The pilot uses this symbology (focussed at
infinity) as well as outside scenario to fly the aircraft
Typical field of view of a HUD is
about 20 degrees by 20 degrees
Flight Instruments: Head Up Display
F16 HUD
Flight Instruments: Head Up Display
HUD Image
Flight Instruments: Head Up Display
F22 HUD front
Flight Instruments: Head Up Display
Example: Solid State
Attitude sensing
system that provides
3 axis angular rate
information to the
computer. This data
generates an attitude
display in the form
of a Vertical
Situation
Indicator,VSI that
eventually displays
all flight perameters,
like shown on the
right.
Flight Instruments: Head Up Display
Aircraft Symbology superimposed on horizon
Major Components of Avionics
Systems(continued)
*** Heads Up Display ( HUD)--Fighters only
# Type of Symbology displayed( monochrome)
## Basic flight and steering
## Navigation guidance
## ILS during Approach for landing
## Weapon release cues
## Warnings and safety cues
Flight Instruments: Head Up Display
Major Components of Avionics
Systems(continued)
*** Color Multifunction Displays( MFD’s)
# Numbers vary from 2 to 8 in different aircraft
# Size varies from 5 x 5 to 8 x 8 ( inches)
# Technology :CRT or Active Matrix LCD
# Scanning : Raster, Cursive or both
# Smart or dumb MFD
# Display is organised in terms of pages
# Page selection by pilot through controls
on MFDs or event driven
Flight Instruments: Multi Function Displays
Multifunction Display Units
Flight Instruments: Multi Function Displays
Some other Displays shown on MFDs:
3 D Terrrain Map
Flight Chart
Engine rpm display
Engine Monitoring parameters
Flight Instruments: Multi Function Displays
Some of the Displays shown on MFDs:
MULTI-FUNCTION DISPLAY MX20
GPS moving map for precision navigation.
Flight Instruments: Miscellaneous Instruments
As mentioned earlier, only precipitation (or objects
more dense than water such as earth or solid structures)
will be displayed on the indicator. The best radar
reflectors are raindrops and wet hail. The larger the
raindrop, the better it reflects. Because large drops in a
concentrated area are characteristic of a thunderstorm,
the radar displays the storm as a strong echo.
Generally, ice, dry snow and dry hail have low
reflective levels and often will not be displayed by the
radar.
Color radars show intensity of echoes by using colors, usually red or magenta as the
most severe (see Weather Radar Display figure, below right). Monochrome radars
use the brightness of the display to indicate intensity.
Extreme weather can usually be identified by characteristic patterns: (1) fingers and
protrusions; (2) hooks; (3) scalloped edges; and (4) U-shaped cloud edges.
Major Components of Avionics
Systems(continued)
*** Color Multifunction Displays( MFD’s)
# Some of the pages are :
For Basic flight and Steering and
Navigation guidance
## Attitude Director Indicator (ADI or SI)
## Horizontal Situation Indicator (HSI )
These are also referred to as Electronics
Flight Instrument System(EFIS)
Flight Instruments: Flight Director Systems
F. ELECTRONIC FLIGHT
INSTRUMENT SYSTEM (EFIS)
EFIS refers to a system where conventional
electro-mechanical flight instruments have been
replaced by cathode ray tubes (CRT). These
CRTs electronically display flight information in
much the same presentation as electromechanical instruments bur they also have the
flexibility for selecting additional information to
be added to the display and for altering the
presentation.
The two most commonly used EFIS instruments
are the electronic horizontal situation indicator
(EHSI) and the electronic attitude director
indicator (EADI) (see EFIS Primary Flight
Display figure, right, and EFIS Navigation
Display figure, next slide).
Flight Instruments: Flight Director Systems
F. ELECTRONIC FLIGHT
INSTRUMENT SYSTEM
(EFIS)
These can also be called an ND (Navigation
Display) or a PFD (Primary Flight Display).
The system may also include a
multifunctional display (MFD) on a larger
CRT which can provide expanded displays
of HSI, radar, and navigation data from flight
instruments and can include other data such
as checklists, emergency procedures, etc.
Data from various sources can be integrated
into various combinations of displays
depending on the equipment installed.
Major Components of Avionics
Systems(continued)
*** Color Multifunction Displays( MFD’s)
# Some of the pages are for(continued) :
## Engine parameters
## Hydraulic System status
## Electrical System status
## Flight Control System status
## Flight Plans
## Ground Maps
Major Components of Avionics
Systems(continued)
*** Color Multifunction Displays( MFD’s)
# Some of the pages are for(continued) :
## Radar displays(many pages)
## Optical and other sensor displays
## Weapon System status
## Maintenance
## Warnings and ‘what to do ‘ Instructions
Major Components of Avionics
Systems(continued)
* Navigation Systems
** Inertial Navigation System(INS)
Self contained Navigation. Does not require any
external reference once INS is ‘ aligned ‘ on the
ground with current Latitude , Longitude
as inputs.
# Platform based or # Strapdown
# Dry Tuned Gyros or Ring Laser Gyros(RLG)
Major Components of Avionics
Systems(continued)
An INS consists of:
# Accelerometers triad:determines acceleration
along triad axis
# Gyroscopes which determine/maintain the
direction of these accelerations along desired
coordinates/axes
Major Components of Avionics
Systems(continued)
An INS consists of:(continued)
# Computer: Integrates acceleration to obtain
velocity and distance traveled(current position)
* Reference Axis/Frame : local vertical
# True North, East, Vertical
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
In a Platform INS( gyros and accelerometers
are kept on a Stabilised Platform )
* Alignment consists of:
# Bringing the ‘ Stabilised Platform’ horizontal
to the Earth’s surface
# Bringing ‘ X ‘ accelerometer to point towards
True North
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
Alignment is done by the INS computer
After Alignment, INS computer continuously
maintains this Stabilised Platform configuration
even as the aircraft
moves over the surface of the Earth
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
**In a Strapdown INS
# Accelerometers are mounted directed on the
aircraft body and the accelerometer axes are
fixed with respect to the aircraft axes.
# Gyros(RLG) continuously determine the
aircraft attitude( pitch, Yaw , Roll) with respect to
the local vertical
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
**In a Strapdown INS ,the computer takes as input :
# Accelerations in body coordinates( aircraft
longitudinal, lateral, and vertical axex)
# Aircraft attitudes( pitch , Yaw , Roll )
with respect to local vertical from RLG
# and computes accelerations and then velocities
and current position in terms of local vertical axes
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
**In a Strapdown INS , alignment consists of
determining the aircraft axes with respect to the local
vertical
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
# Major outputs of an INS
## Current Position( Lat, Long , Baro-inertial Alt)
Baro-Inertial Alt : combination of Barometric
and Inertial altitude
## Aircraft Body rates or velocities
## Aircraft Body accelerations
## Aircraft Pitch, Heading and Roll
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
# Major outputs of an INS
## Aircraft current Velocities( Ve, Vn, Vd)
## Ground Speed
## Aircraft Track( or Ground Track)
## Aircraft Heading
Major Components of Avionics
Systems(continued)
** Inertial Navigation System(INS)
# Typical Position Accuacy ;
0.5 - 1.0 Nautical mile / hour
# INS suffers from gyro drift and position and
velocity accuracy degrades with time
# Hybrid INS + GPS
Major Components of Avionics
Systems(continued)
** Attitude and Heading Reference System(AHRS)
# provides Attitude and Heading Reference to be
displayed to the pilot
# Consists of set of Gyroscopes and a Compass
Major Components of Avionics
Systems(continued)
* Radio Navigation Aids
** Tactical Air Navigation ( TACAN)
# secondary radar ( 960-1215 MHZ)
# Provides Range and bearing to a TACAN station
** VHF OMNI Range ( VOR)
# provides bearing to a VOR station
# 108 -136 MHZ
Major Components of Avionics
Systems(continued)
* Identification Friend or Foe ( IFF)
# Secondary Radar ( L Band)
# 3 main modes
# Transmit identification code when interrogated
by a ground station(radar)
Also transmits aircraft air data to ground station
Major Components of Avionics
Systems(continued)
* Instrument Landing System ( ILS)
# Aid to approach and Landing
# Consists of
## Localiser( 108-110 MHZ) which provides
info on deviation from runway center line
## Glide Slope unit ( 335-339 MHZ) which
provides info on deviation from desired angle
of descent( generally between 2 - 4 degrees)
Major Components of Avionics
Systems(continued)
* Instrument Landing System ( ILS)
# Aid to approach and Landing
# Consists of
## Marker Beacons( Inner, Middle, Outer ) 75 MHZ
These beacons help the pilot check his position in
in approach path as he flies over the beacons
Major Components of Avionics
Systems(continued)
* Communication Systems
# HF for long Range
# VHF / UHF line of sight ( main and stby)
** need for several channel : eg.
## Air Traffic Control
## Interception/Recovery
## Various Air Route Surveillance Radars
## Emergency
## GCA
Major Components of Avionics
Systems(continued)
* Autopilot
** Relieves Pilot of tedium , particularly during long
flights.
# Main modes
## Heading hold
## Heading Select / Acquire
## Altitude hold
## Altitude Select / Acquire
## Attitude hold
Major Components of Avionics
Systems(continued)
* Radars
# Fire Control, Terrain Following, etc
# Weather
* Laser Rangers/Laser Designators
* Forward Looking Infrared Radar( FLIR)
* Electronic Warfare Systems
* Air Data Computer : Pressure Altitude, Airspeed
Mach No.
Major Components of Avionics
Systems(continued)
* Cabin Intercommunication Systems
* Entertainment Systems: Audio Channels, video Channels,
personal TV’s
* Radio Altimeter
* Collision Avoidance System (TCAS)
* Flight Control System Computers
Major Components of Avionics
Systems(continued)
* Mission Computer
# Integrates all Sensors, Navigation aids, Cockpit
Displays and Controls ,Air Data Computer, Symbol
Generators or Display Processors ,Weapons,
Flight Controls systems, Autopilot, Electronic
Warfare systems, Engine monitoring unit ,etc
In short,
Integrates all electronic systems in the aircraft
Major Components of Avionics
Systems(continued)
* In most Commercial aircraft,
there is a Flight Management Computer instead of a
Mission Computer as the integrating computer.
As Flight Management is the main mission function
in a commercial aircraft
Avionics Architecture
Evolution
* Independent ( Analog )Avionics ( 1940-1950’s)
* Federated Avionics ( 1960-1970’s)
* Integrated Avionics ( 1980-1990’s)
Avionics Architecture
* Independent ( Analog )Avionics ( 1940-1950’s)
Each functional area has separate, dedicated sensors,
processors and displays and the interconnect media is
point to point wiring
AVIONICS ARCHITECTURE
* INDEPENDENT AVIONICS (1940’S - 1950’S)
DISPLAY
RADAR
CONTROLS
CONTROLS
TACAN
DISPLAY
CONTROLS
VOR/DME
DISPLAY
CONTROLS
ADC
DISPLAY
Avionics Architecture
* Federated Avionics ( 1960-1970’s)
* Typical of most military and commercial
avionics flying today
* Resource sharing occurs at the last link in the
information chain, via controls and displays.
* Use of time shared multiplexed data buses
1553 B, Stanag 3910
* Standard data processors used to perform
variety of low bandwidth functions like:
Avionics Architecture
* Federated Avionics ( 1960-1970’s)(continued)
navigation, weapon delivery,stores management
and flight control
* All high speed data processing and signal processing
done inside ‘ black boxes ‘ or LRU’s
* LRU ( Line Replaceable Unit)
* Such architectures simplified physical integration
and retrofit problems
Avionics Architecture
* Federated Avionics ( 1960-1970’s)(continued)
# Generally, the distributed processing concept consists of :
## Sensor oriented functions are performed by
various sensor computers
INS, Radar, LDP, Communication units, NAV aids,etc
## Mission oriented functions are performed by
a central Mission Computer or a Flight
Management Computer
Avionics Architecture
* Federated Avionics ( 1960-1970’s)(continued)
## Cockpit man machine equipment functions are
performed by Display Processors/Symbol
Generation units and various Control panels and
Display surfaces
AVIONICS ARCHITECTURE
* FEDERATED AVIONICS (1960’S - 1970’S)
INS
RA
CONTROL
PANELS
RADAR
MIL STD
1553 B
SGC
HUD
MFD’S
V/ UHF
SMS
MISSION
COMPUTER
Avionics Architecture
* Integrated Avionics ( 1980-1990’s)
** Also called ‘Integrated Digital Avionics or
PAVE PILLAR Architecture
** Boeing 777
** Higher level of Integration
** Use of a small family of line replaceable modules
(LRM’s) to do all types of Signal and Data
Processing
Avionics Architecture
* Integrated Avionics ( 1980-1990’s)(continued)
** Reduces maintenance effort, allows System
reconfiguration in real time , cost reduction through
common replicated modules
Avionics Architecture
* Integrated Avionics ( 1980-1990’s)(continued)
# Generally, the distributed processing concept consists of :
## Common Integrated Processing modules performing
various signal and data processing tasks.Real time
reconfiguration is a great benefit. There are no
individual units identifiable as a Radar, INS, ADC
LDP, etc.
## Individual RF and Sensing assemblies ( eg. RLG)
will be there
Avionics Architecture
* Integrated Avionics ( 1980-1990’s)(continued)
## Control Panels and Display Surfaces will be shared
as in Federated Avionics
AVIONICS ARCHITECTURE
* INTEGRATED AVIONICS (1980’s - 1990’s)
RADAR
RF
INS
RLG
RA
RF
LDP
OPTICAL
BANK OF
COMMON
INTEGRATED
PROCESSORS
(DSP & DATA)
DISPLAYS
CONTROLS
Avionics Mission Functions
* Navigation Functions
* Air to Air Missiles/Gun functions
* Air to Ground/Sea Missiles/Gun/Bombs functions
The last two set of functions are for military aircraft only
Avionics Mission Functions
* Navigation Functions
# Basic Flight and Steering
# Navigation Guidance
## Direct Track Guidance
## Speed Guidance
## Desired Track Guidance
## Route Navigation or Automatic switch over
Navigation
## Approach for landing
Avionics Mission Functions
* Navigation Functions
# Basic Flight and Steering
This function helps the pilot to :
## Taxi
## Take off
## Perform Basic flying and Steering of the
Aircraft
Avionics Mission Functions
* Navigation Functions
# Basic Flight and Steering
## The pilot uses symbology on the HUD as well as
symbology on the MFD’s
## In addition the pilotalso uses conventional
Instruments like Artificial Horizon,
ASI, ROCI, Altimeter,AOA indicator
Compass,etc
Avionics Mission Functions
# Basic Flight and Steering(continued)
## Some parameters displayed on the HUD
* Heading,Track,Drift
* Airspeed, Angle of Attack,Mach No.
* Horizon bar and pitch/roll bars
* Velocity vector
* Pressure Altitude & Baro-Inertial Altitude
* Ground speed
Avionics Mission Functions
# Basic Flight and Steering(continued)
## Some parameters displayed on the MFD
* Most parameters displayed on the HUD
* Attitude Direction Indicator( ADI or EFIS)
Avionics Mission Functions
# Navigation Guidance
Definitions
All Guidance is to a ‘ Waypoint ‘ or an ‘Offset Point ‘
A waypoint is defined by
* Latitude , Longitude , Altitude ( above msl)
An Offset Point is defined with respect to a waypoint
* Delta Latitude, Delta Longitude,
Delta Altitude
Avionics Mission Functions
Definitions(continued)
Flight Plan
* An ordered or sequential list of Waypoints
or Offset Points is a flight plan.
Order No.
Waypoint/ Offset point No.
1
5
2
6* ( offset to wp 6)
3
18
4
3
Avionics Mission Functions
# Navigation Guidance
## Direct Track Guidance
Guidance to go to a Waypoint directly from
the aircraft current position
Cues are displayed to the pilot on the HUD
and MFD. The parameters displayed are ;
* Range and bearing to Waypoint
Avionics Mission Functions
# Navigation Guidance
## Direct Track Guidance
* Deviation required from aircraft current
Track to reach the Waypoint
* Horizontal Situation Indicator(HSI) on
MFD(EFIS). An HSI indicates:
** Heading , Track, Range and bearing to
WP, Altitude,Airspeed, ground speed,
Mach No.
Avionics Mission Functions
# Navigation Guidance
## Desired Track Guidance
Guidance to approach a WP along a Desired
Track. This could be to avoid missile and
ground defences. It could also be used to
approach a busy airport along a certain path
Information displayed on HUD/MFD is similar to that
displayed in the case of Direct Track
Avionics Mission Functions
# Navigation Guidance
## Speed Guidance
This function gives a Pilot cues to reach a WP at a
specific absolute time or a relative time with
respect to the time at the previous WP
Speed Guidance cues( reduce speed, increase speed,
maintain speed, time to go ) are displayed to the pilot on the
HUD and MFD(HSI page)
Avionics Mission Functions
# Navigation Guidance
## Route Navigation or Automatic Switch Over
Navigation
This function displays guidance cues to take
an aircraft sequentially from one WP to another WP
according to the Flight Plan. Flight plans are entered into
the Avionics System at start up. Both speed guidance and
direct track guidance can be superposed with this function.
Avionics Mission Functions
# Navigation Guidance
## Route Navigation or Automatic Switch Over
Navigation
Route Navigation parameters( Current WP, Next WP,
Flight Plan No.) are displayed on the HUD/MFD(HSI)
A separate Flight Plan map page on the MFD displays all
the WP’s in the selected Flight Plan along with the aircraft
current position
ROUTE NAVIGATION
* FLIGHT PLAN MAP
W22
W31
W18
W16
TN
Avionics Mission Functions
# Navigation Guidance
## Approach
In addition to Basic flight and steering
symbology , Approach cues to the airport and landing cues(
runway heading, length, synthetic runway symbology, glide
slope , ILS localiser and glide slope ‘what to do ‘
parameters) are displayed on the HUD/MFD’s
Flight Instruments: Flight Director Systems
1. PRIMARY FLIGHT DISPLAY
(PFD): The typical PFD is a multicolor CRT or
LCD display unit that presents a display of aircraft
attitude and flight control system steering
commands including VOR, localizer, TACAN, or
RNAV deviation; and glideslope or preselected
altitude deviation. Flight control system mode
annunciation, auto-pilot engage annunciation,
attitude source annunciation, marker beacon
annunciation, radar altitude, decision height set and
annunciation, fast-slow deviation or angle-altitude
alert, and excessive ILS deviation (when Category
II configured) can also be displayed (see EFIS
Primary Flight Display figure, right).
Flight Instruments: Flight Director Systems
2. NAVIGATION DISPLAY (ND): The typical ND
is a multicolor CRT or LCD display unit that
presents a plan view of the aircraft horizontal
navigation situation. Information displayed includes
compass heading, selected heading, selected VOR,
localizer, or RNAV course and deviation (including
annunciation or deviation type), navigation source
annunciation, digital selected course/desired track
readout, excessive ILS deviation (when Category II
configured), to/from information, back course
localizer annunciation, distance to station/waypoint,
glideslope MGP, or VNAV deviation ground speed,
time-to-go, elapsed time or wind, course
information and source annunciation from a second navigation source, weather radar
target alert, waypoint alert when RNAV is the navigation source, and a bearing pointer
that can be driven by VOR, RNAV or ADF sources as selected on the display select
panel. The ND can also be operated in an approach format or an en route format with
or without weather radar information included in the display (see EFIS Navigation
Display figure, above right).
Flight Instruments: Flight Director Systems
For outbound tracking, the pilot selects
the desired track in the selector
window and ensures that the TOFROM indicator points toward the tail
of the track arrow. The pilot then turns
the aircraft in the shortest direction to
an interception track that places the
head of the track arrow in the upper
half of the HSI with a suitable
interception angle (normally 45°).
Immediately after passing the station,
the pilot intercepts the outbound track
by turning the aircraft to parallel the
track. The pilot sets the outbound track
in the selector window. When the track
bar and bearing pointer stabilize, the
pilot notes the degrees off track and
turns towards the track by this amount,
allowing for wind drift. The intercept
angle should not exceed 45°.
Flight Instruments: Flight Director Systems
C. HORIZONTAL SITUATION INDICATOR
The HSI provides a basic horizontal view of the
aircraft's navigation picture. In the F-15E, it can
provide navigation data to selected ground
navigation facilities (TACAN or Instrument
Landing System (ILS)) or to onboard navigation
systems like the Inertial Navigation System (INS).
Instrument flying without an HSI requires a fair
amount of mental gymnastics; for this reason, the
HSI is becoming more prevalent in general
aviation since it provides an excellent picture for
precise navigation.
The electronic HSI in the F-15E provides a wealth of information. In the example
above, the HSI provides the crew with the bearing and range to the selected TACAN (a
ground based navigation instrument that transmits a signal 360 degrees from the
station) is 305 degrees and 16.0 miles (the time required to fly to the TACAN is 2
minutes and 20 seconds); the bearing and distance to the point the INS is steering to is
105 degrees and 12 miles (the time required to fly to the INS steering point is 1 minute
and 48 seconds).
Flight Instruments: Flight Director Systems
The horizontal situation indicator (HSI) was
developed to assist pilots to interpret and use
aircraft navigational aids. There are various types
of HSIs, but each performs the same function. The
HSI (see figure, right) displays information
obtained from combinations of the heading
indicator, radio magnetic indicator (RMI), track
indicator and range indicator. It may also display
VOR, DME, ILS or ADF information.
The aircraft heading is displayed on a rotating
compass card under the heading lubber line. The
card is calibrated in 5° increments.
The hearing pointer provides magnetic bearing information from the aircraft to the
selected ground station (VOR or ADF). The fixed aircraft symbol and floating track
bar display the aircraft's position relative to the selected track (VOR or ILS localizer).
When a VOR station is selected, the inner dot on the track bar azimuth scale indicates
approximately 5° and the outer dot approximately 10° (the aircraft's operating manual
should give details).