10. INS & GPS - N2 Flashcards
What is INS?
Inertial Navigation system.
Using motion sensors and gyros
Dead reckoning
If you know where an aircraft starts from, and how far it has subsequently moved in any given direction, then you will also know its current position.
What can be displayed to a pilot from the INS? (8)
- TR/GS - Aircraft track and groundspeed
- HDG/DA - Heading and drift angle
- XTR/TRE - Dist. off track and track angle error
- POS - Current position
- WAY/PT - Waypoint insertion and viewing
- DIS/TIME - Distance and time to next waypoint
- WIND - Current wind velocity
- **DSRTR/STS - Desired track to next waypoint and system status
How does the INS start up?
Pilot inputs lat and long
Presses Align
Platform levels itself
INS aligns with true north
Select NAV
What is GNSS?
Global Navigation Satellite System (GNSS) refers
to a constellation of satellites providing signals
from space that transmit positioning and timing
data to GNSS receivers. The receivers then use
this data to determine location.
Examples of GNSS?
Europe’s Galileo.
USA’s NAVSTAR Global Positioning System (GPS).
Russia’s Global’naya Navigatsionnaya Sputnikovaya Sistema (GLONASS).
China’s BeiDou Navigation Satellite System.
GPS
The GPS satellites circle the earth every 12
hours in a very precise orbit and transmit signal
information to earth.
GPS receivers triangulate to calculate the user’s exact location.
Using time between satalite and receiver.
GPS is capable of Precision Approach Guidance
down to Cat 1 limits.
The more satellites in view, the more accurate
the position.
The performance of GNSS (4)
-
Accuracy: the difference between a receiver’s
measured and real position, speed or time. - Integrity: a system’s capacity to provide a threshold of confidence and, in the event of an anomaly in the positioning data, an alarm.
- Continuity: a system’s ability to function without interruption.
- Availability: the percentage of time a signal fulfils the above accuracy, integrity and continuity criteria.
Sources of error in GPS (5)
- Ionosphere and Troposphere Delays
- Orbital errors
- Satellite Geometry and shading - wide angle of SAT
- Receiver clock error
- signal multi path - reflections of buildings
How to correct errors in GPS?
ABAS - Airborne based Augmentation System. (RAIM)
GBAS - Ground Based (Differential GPS)
SBAS - Satellite Based (WAAS, EGNOS)
What is ABAS?
Aircraft Based Augmentation system
Augments and/or integrates the information
obtained from the GNSS elements with other
information available on board the aircraft (INS).
(RAIM - receiver based & AAIM - using on board systems INS)
What is GBAS?
Ground Based Augmentation System
Local Area Augmentation System is the ICAO
definition ground-based augmentation for
Satellite Navigation.
GBAS is the European application of LAAS.
Differential GPS is an Example.
What is DGPS?
Differential GPS
Accuracy can be improved by combining the GPS
receiver with a Differential GPS (or DGPS) receiver.
DGPS.
What is SBAS?
Satallite Based Augmentation System
SBAS is a generic term for GNSS augmentations,
which use geostationary satellites to broadcast
information to users over a large geographical area.
European EGNOS (European Geostationary
Navigation Overlay Service)
Similar to DGPS but uses two satellites to further
correct readings together with ground stations.
Future satallite systems
GALILEO (Operational circa 2020)
Japan’s Quasi-Zenith Satellite System (QZSS)
Indian Regional Navigation Satellite System
(IRNSS)
Space X Constellation
How is GNSS performance assessed?
using 4 criteria: Accuracy; Integrity; Continuity; Availability
