NAV - INS & GPS Flashcards
What is INS? (4)
INS - Inertial Navigation System
- Uses Rotation sensors to continuously calculate by dead reckoning
- Dead reckoning the orientation, velocity, of a moving object without the need for external references
- Cannot be restarted once in-flight so triple systems for redundancy protection
What Axis’s are used for an INS? (3)
- Forwards = X
- Sideways = Y
- Vertically = Z
(acceleration = change of velocity)
How does an INS interpret movement? (3)
- Interprets Movement in relation to change of latitude and longitude
- Receives continuous input from the aircraft’s magnetic compass system
Also:
What can a triangle of velocity show?
show that INS instantaneously solves the navigation problem and presents the pilot with instant readings
What can the Pilot input and receive on the flight deck with INS? (8)
- Aircraft track and groundspeed (TR/GS)
- Heading and drift angle (HDG/DA)
- Dist. off track and track angle error (XTR/TRE)
- Current position (POS)
- Waypoint insertion and viewing (WAY/PT)
- Distance and time to next waypoint (DIS/TIME)
- Current wind velocity (WIND)
- Desired track to next waypoint and system status (DSRTR/STS)
Inertial Platform diagram
- The Mounting Board for the Accelerometers
- It contains gyroscopes that ensure it remains level with regard to the surface of the Earth
- Modern systems incorporate laser ring gyroscopes to eliminate the problem of drift
What type of North does the INS find during its alignment? (1)
True north
What does the system select when its alignment is completed? (1)
“Nav”
What will happen is an Aircraft is moving prior to alignment completion? (2)
- Invalidates the alignment prior to selecting Nav
- Sequence has to be repeated
INS is a stand-alone system using accelerometers on a gyroscopic platform to calculate movement in all 3 dimensions. True or False?
True
What is GNSS? (2)
GNSS - Global Navigation Satellite System
- Satellites providing signals from space that transmit positioning and timing data to GNSS receivers
What types of GNSS global coverage is available? (4)
- Galileo - Europe
- NAVSTAR - USA
- GLONASS - Russia
- BeiDou - China
How often do GPS satellites travel around the Earth? (1)
- Every 12 hours in a precise orbit
How does a GPS work? (4)
- Transmitting signal information to Earth
- Use triangulation to calculate the user’s exact location
- Compares time from signal transmission to when the signal is received
- Time difference tells the GPS receiver how far away the satellite is
What Category level is a GPS capable of being for a precision approach? (1)
Capable to Cat I limits
GPS operation diagram
The more satellites in view, the more accurate
the position
How is the performance of GNSS assessed? (4)
- Accuracy
- Availability
- Integrity
- Continuity
What errors do civilian GPS receivers encounter? (2)
- Ionosphere and Troposphere Delays
- Orbital errors
How do satellites work with their Geometry? (2)
- The wider the angle between the satellites, the better the accuracy of the measurement
- Poor geometry results when the satellites are located in a line or in a tight grouping
What types of geometry / shading error can occur for GPS? (3)
- Receiver clock errors
- Number of satellites visible
- Signal multi-path
How is satellite geometry / shading corrected? (3)
- ABAS - Airborne based Augmentation System. (RAIM)
- GBAS - Ground Based (Differential GPS)
- SBAS - Satellite Based (WAAS, EGNOS)
What is ABAS? (3)
ABAS - Airborne Based Augmentation System
- Augments and/or integrates the information obtained from the GNSS elements with other information available on board the aircraft INS
- Improves: Integrity, availability, accuracy
What 2 techniques does ABAS use? (2)
- RAIM - Receiver Autonomous Integrity System
- LAAS - Local Area Augmentation System
What is DGPS? (6)
DGPS - Differential GPS
- Works by placing a GPSreceiver (called a reference station) at a known location
- Can determine the errors in the satellite signals
- Measures ranges to each satellite
- The difference between the measured and calculated range becomes a “differential correction”
- Corrections are then applied to the GPS receiver’s calculations, removing many of the common errors and improving accuracy
What is SBAS? (3)
SBAS - Satellite Based Augmentation System
- A generic term for GNSS augmentations, which use geostationary satellites to broadcast information to users over a large geographical area
- Similar to DGPS but uses two satellites to further correct readings together with ground stations
