Navigation Aids: GNSS

Question 1

What does the GNSS system include?

Answer 1

1) One or more satellite constellations
2) Aircraft Receivers
3) System integrity monitoring
4) Augmentation (error correction for improved accuracy)

Question 2

What are the four major GNSS systems?

Answer 2

1) GPS (for the USA)
2) GLONASS (for Russia)
3) Galileo (EU)
4) BeiDou (Chinese)

Question 3

What is the only permitted GNSS for IFR flights in Australia?

Answer 3

GPS (USA) system

Question 4

What do GNSS satellites and other system components do?

Answer 4

• Broadcast signals that A/C receivers can interrogate in order to establish accurate position and time references.

Question 5

What frequency does GNSS use?

Answer 5

UHF transmissions.

Question 6

What are the two levels of service that the USA’s GPS provides?

Answer 6

1) Standard positioning

2) Precise positioning

Question 7

Who can use precise positioning GPS satellites?

Answer 7

US military and approved foreign powers.

Question 8

How many satellites are required for A/C navigation?

Answer 8

4

Question 9

What are the three elements of the GPS system?

Answer 9

1) Space Segment
2) Control Segment
3) User Segment

Question 10

What are the GPS errors and limitations?

Answer 10

1) Ephemeris error - An error inherent in the data that defines the satellites current position
2) Ionospheric errors occur due to the change of the speed of light and therefore the ionosphere refract and reflect the signal, especially for an observer with a GPS satellite closer to the horizon.
3) Tropospheric Propagation effect - water vapor in the troposphere delays the satellite signal propagation, inducing ranging errors.
4) Multipath error - occurs when GPS signal bounces off multiple surfaces before arriving at the receiver
5) Clock error- Occurs when satellite’s atomic clock becomes out of alignment with the reference clock.
6) Receiver noise - Unwanted disturbances superimposed on a signal that obscures the signal’s usefulness.

Question 11

What does the GNSS receiver do?

Answer 11

Uses the signals of at least 4 of the best-positioned satellites to yield a 3-d fix (lat, long, altitude).

Question 12

What can be used to improve the integrity of the data?

Answer 12

Ground, air based augmentation systems.

Question 13

What are the two current Aircraft Based Augmentation Systems (ABAS) currently in use?

Answer 13

1) Receiver Autonomous Integrity Monitoring (RAIM) - used to determine if a satellite is providing corrupted information. (5 satellites required)
2) Aircraft Autonomous Integrity Monitor (AAIM) - use the position from the aircraft’s inertial navigation system and other sensors as an integrity check of the GNSS solution, when RAIM is unavailable.

Question 14

How many Global Landing System Sensor Units (GLSSU) are installed on the PC-21?

Answer 14

2

Question 15

What are the GLSSU system components?

Answer 15

• 2 GLSSU units

- 2 GLSSU antennas

Question 16

What are the primary functions of the GLSSU?

Answer 16

1) Receiver the radio frequency signals from each satellite through the antennas
2) Compare received and transmitted coded signals and calculate a range to each satellite
3) Calculate aircraft position through triangulation of multiple satellite ranges.

Question 17

What should always be done to minimize human error?

Answer 17

1) Always cross checking manually entered data against relevant and current nav charts
2) Using data from a valid and current database
3) Cross checking nav info with other radio nav aids.