Navigation part 1 Flashcards
Heading
compass direction which the aircraft is pointing
Wind velocity
speed and direction of the wind relative to the surface of the earth
Ground speed
aircraft speed relative to the surface of the earth
Course
the required ground trace to a waypoint or beacon
Track
the path traced on the surface of the earth by aircraft vertically overhead
Bearing
magnetic direction to a given object/location
Waypoints
predetermined geographical reference point defined by latitude and longitude coordinates ground-based beacons used to indicate fly-by or fly-over information and change in direction
Navigation systems
short or long-range - ground station-based systems global coverage - satellite systems autonomous-air data and/or inertial systems
Radio navigation aids and communication frequency bands
HF-high frequency VHF- very high frequency UHF- ultra high frequency
HF
3-30MHz beyond line of sight long-range communications via skywave propagation(ionospheric refraction)
VHF
30-300MHz line of sight VOR-navigation beacons instrument landing systems civilian communications
UHF
300-3000MHz line of sight DME-navigation beacons global navigation satellite systems military communications
Limitations of short range navaids
- performance is relatively consistent-not affected by ionospheric variation
- subject to the line of sight limitation of VHF communications
- Line of sight range nautical miles (nm) = 1.23√h1(ft) + 1.23√h2(ft)
- significant infrastructure required
- considerations of dessert or oceanic crossings
VOR
VHF omnirange VOR uses VHF for bearing pilot tunes navigation receiver into the VHF frequency ground station radiates 2 signals on VHF band phase difference between signal provides the radial on which the aircraft flies
DME
DME uses UHF for range but is frequency paired the user selects only VOR/UHF frequency to get both range and bearing transponder based aircraft equipment DME unit interrogates the ground station and measures the time to reply
GPS system
control - ground stations providing monitoring and control space- satellites user - GPS receivers, any number of users
GPS principle
receiver system knows position of all satellites GPS receivers measure Time of Arrival and receives Time of Transmission of signals from 4 satellites and from this, the Time of Flight values are computed 3D position of the aircraft and offset of receiver clock are computed simultaneously using the navigation equations At lease 4 satellites are required to resolve 4 equations
GPS Augmentation
augmentations ar methods used to improve the reliability, accuracy and availability of the system by considering the integration of external information into the calculations
ABAS- aircraft based augmentation
receiver autonomous integrity monitoring(RAIM) uses redundant satellites to monitor and predict actual performance improves accuracy, reliability and availability of GPS navigation absolute minimum in GPS aircraft navigation
External augmentation- differential GPS concept
correction signals are derived from the difference between the GPS computed positions of ground stations and their actual surveyed locations stations broadcast the difference between the measured and actual pseudoranges GPS users correct their pseudoranges according
SBAS satellite based augmentation
corrections over large areas allow aircraft to rely on GPS for all phases of flight including approaches on runways network of ground reference stations measure variations in signal master stations send deviation corrections to SBAS satellites for broadcast to users high accuracy high integrity high availability
GBAS- ground bases augmentation
corrections over a small area allows precision GPS instrument approaches GLS which can be used in all weather conditions it is based on real-time differential correction of the GPS signal within a local area corrections are sent via VHF data link on ILS freq ~110MHz
Other GNSS
GLONASS - russian system GALILEO-European system planned for operation in 2020 low precision position for free high precision for commercial users with 1m precision transponder function to relay distress signals from emergency beacons
Autonomous nav aids
inertial navigation initialised with aircraft lat/long. coordinates / GPS position at parking position in departure airport inertial sensors accelerometer gyro measurements relative to the inertial frame
Rigid platform
IRS fixed to airframe, measurements from the body frame solid state components Ring laser gyro used increased accuracy and reliability compared to rotating gyro
Stable platform
gyros control gimbal servos platform axis remains fixed in space accelerometers and gyros mounted on the platform
INS characteristics
dead reckoning navigation autonomous and self contained high update rates 100MHz no external interference indirect position, velocity and altitude very accurate but accuracy drifts with time
GNSS characteristics
relies of satellite availability susceptible to jamming/RF interference accuracy
