RAD 19 - GNSS - Pilotexam.in

📄 Detailed Notes ⚡ Cheat Sheet

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📄 Notes ⚡ Cheat Sheet

Q1. In Satellite navigation PRN stands for:

Pseudo Random Noise

Precise Navigation Noise

Pseudo Radio Navigation

Pseudo Navigation Range

[Pseudo Random Noise] –

Step 1: Identify the acronym used for GPS signal coding.
Step 2: PRN (Pseudo-Random Noise) is a binary code unique to each satellite.
Step 3: It allows the receiver to identify the satellite and calculate signal travel time.

Q2. Which GPS frequencies are available for commercial air transport?

1575.42 MHz only

1227.6 MHz only

1227.6 MHz or 1575.42 MHz

1227.6 MHz and 1575.42 MHz

[1575.42 MHz only] –

Step 1: GPS transmits on two primary L-band frequencies: L1 and L2.

Step 2: L1 (1575.42 MHz) carries the C/A code for civilian use.

Step 3: L2 (1227.6 MHz) is primarily used for military P(Y) code and ionospheric correction.

Q3. The orbital height and inclination of the NAVSTAR/GPS constellation are:

19 099 km, 65 deg

19 099 km, 55 deg

20 180 km, 55 deg

20 180 km, 65 deg

[20 180 km, 55 deg] –

Step 1: Recall the MEO (Medium Earth Orbit) parameters for NAVSTAR.

Step 2: The standard altitude is approximately 20,180 km (approx. 10,900 NM).

Step 3: The orbital planes are inclined at 55 deg to the equator.

Q4. The orbital planes of the satellite navigation system NAVSTAR/GPS are:

inclined 55 deg to the equatorial plane

inclined 55 deg to the earth axis

inclined 90 deg to the equatorial plane

parallel to the equatorial plane

[inclined 55 deg to the equatorial plane] –

Step 1: Define the reference for orbital inclination.

Step 2: NAVSTAR uses 6 orbital planes.

Step 3: Each plane is inclined 55 degrees relative to the Earth’s equator to provide global coverage.

Q5. The NAVSTAR/GPS operational constellation comprises how many satellites?

[24] –

Step 1: Identify the baseline operational design of NAVSTAR.

Step 2: The system is designed with 24 satellites (21 active + 3 spares).

Step 3: This ensures at least 4-6 satellites are in view from any point on Earth.

Q6. The model of the earth used for NAVSTAR/GPS is:

PZ84

PZ90

WGS90

WGS84

[WGS84] –

Step 1: Identify the geodetic datum used by GPS.

Step 2: World Geodetic System 1984 (WGS84) is the standard ellipsoid model.

Step 3: All GPS coordinates and altitudes are referenced to this mathematical model.

Q7. The NAVSTAR/GPS reference system is:

A geo-centred 3D Cartesian coordinate system fixed with reference to space

A geo-centred 3D system based on latitude, longitude and altitude

A geo-centred 3D Cartesian coordinate system fixed with reference to the sun

A geo-centred 3D Cartesian coordinate system fixed with reference to the prime meridian, equator and pole

[A geo-centred 3D Cartesian coordinate system fixed with reference to the prime meridian, equator and pole] –

Step 1: Describe the Earth-Centered, Earth-Fixed (ECEF) system.

Step 2: It is a 3D Cartesian (X, Y, Z) system.

Step 3: It rotates with the Earth, using the equator, prime meridian, and poles as axes.

Q8. The number of satellites required to provide a 3D fix without RAIM is:

3D fix – without RAM — 4SV
3D fix with RAIM — 5SV
3D fix with RAIM, allow loss of one — 6SV

To keep RAIM you need 5/6 satellite.

Q9. The NAVSTAR/GPS segments are:

space, control, ground

space, control, user

space, control, air

space, ground, air

[space, control, user] –

Step 1: Identify the three functional divisions of the system.

Step 2: Space Segment (Satellites), Control Segment (Ground stations), User Segment (Receivers).

Q10. The minimum number of satellites required for receiver autonomous integrity monitoring (RAIM) is:

[5] –

Step 1: Define RAIM function for fault detection.

Step 2: 4 satellites are needed for a 3D fix.

Step 3: A 5th satellite is required to detect an inconsistency (fault) among the signals.

Q11. The most accurate fixing information will be obtained from:

four satellites spaced 90 deg apart at 30 deg above the visual horizon

one satellite directly overhead and 3 spaced 120 deg apart close to the horizon

one satellite directly overhead and 3 equally spaced at 60 deg above the horizon

one satellite close to the horizon and 3 equally at 60 deg above the horizon

[one satellite directly overhead and 3 spaced 120 deg apart close to the horizon] –

Step 1: Identify the geometry that minimizes DOP (Dilution of Precision).

Step 2: High accuracy requires large angular separation between satellites.

Step 3: One overhead and three spread around the horizon provides the best geometric volume.

Q12. An all-in view receiver:

checks all the satellites in view and selects the 4 with the best geometry for fixing

uses all the satellites in view for fixing

informs the operator that all the satellites required for fixing and RAIM are in available

requires 5 satellites to produce a 4D fix

[checks all the satellites in view and selects the 4 with the best geometry for fixing] –

Step 1: Explain “all-in-view” capability.

Step 2: The receiver tracks every visible satellite.

Step 3: It then mathematically selects the combination that yields the lowest PDOP.

Q13. Unauthorized’ civilian users of NAVSTAR/GPS can access:

the C/A and P codes

the P code

the P and Y codes

the C/A code

[the C/A code] –

Step 1: Distinguish between PPS and SPS.

Step 2: Standard Positioning Service (SPS) for civilians uses the Coarse/Acquisition (C/A) code.

Step 3: The Precision (P) and encrypted (Y) codes are reserved for authorized/military use.

Q14. To provide 3D fixing with RAIM and allowing for the loss of one satellite requires …………. SVs:

[6] –

Step 1: Calculate the redundancy needed for Fault Detection and Exclusion (FDE).

Step 2: 5 satellites are needed for RAIM (detection).

Step 3: A 6th is needed to exclude a faulty satellite and maintain a 3D fix without interruption.

Q15. When using GNSS to carry out a non-precision approach the MDA will be determined using:

GPS altitude

radio altimeter height

either barometric or radio altimeter altitude

barometric altitude

[barometric altitude] –

Step 1: Identify the vertical reference for Non-Precision Approaches (NPA).

Step 2: GPS vertical accuracy is generally lower than lateral accuracy.

Step 3: Per regulation, the MDA must be flown using the pressure (barometric) altimeter.

Q16. The most significant error of GNSS is:

ephemeris

receiver clock

ionospheric propagation

PDOP

[ionospheric propagation] –

Step 1: Identify the largest source of signal delay.

Step 2: Radio waves slow down when passing through the ionosphere.

Step 3: This variable delay causes the most significant distance error in single-frequency receivers.

Q17. The position derived from NAVSTAR/GPS satellites may be subject to the following errors:

ephemeris, PDOP, siting

PDOP, static interference, instrument

propagation, selective availability, ephemeris

selective availability, sky wave interference, PDOP

[propagation, selective availability, ephemeris] –

Step 1: List standard GPS error sources.

Step 2: Includes ionospheric delay (propagation), orbital data errors (ephemeris), and intentional degradation (SA).

Step 3: PDOP is a geometry factor, not an inherent signal error.

Q18. The availability of two frequencies in GNSS:

reduces propagation errors

reduces errors caused by PDOP

removes SV ephemeris and clock errors

removes receiver clock errors

[reduces propagation errors] –

Step 1: Explain dual-frequency (L1/L2) benefits.

Step 2: Ionospheric delay is frequency-dependent.

Step 3: Comparing the arrival times of two frequencies allows the receiver to calculate and subtract the delay.

Q19. An aircraft GNSS receiver is using 5 satellites for RAIM. If the receiver deselects one satellite then the flight should be continued:

using inertial reference systems only

using 4 satellites with the pilot monitoring the receiver output

using alternative radio navigation systems only

using alternative navigation systems

[using alternative navigation systems] –

Step 1: Assess RAIM status with 4 satellites.

Step 2: With 4 satellites, you have a fix but no integrity monitoring.

Step 3: Pilot must revert to or cross-check with alternative aids (VOR, DME, etc.).

Q20. The positioning of a GNSS aerial on an aircraft is:

under the fuselage

on top of the fuselage close to the centre of gravity

on the fuselage as close as possible to the receiver

in the fin

[on top of the fuselage close to the centre of gravity] –

Step 1: Determine antenna visibility requirements.

Step 2: The antenna requires a clear sky view for satellite line-of-sight.

Step 3: Placement on top of the fuselage, typically near the CG, minimizes shadowing during maneuvers.

Q21. If a receiver has to download the almanac, the time to do this will be:

2.5 minutes

12.5 minutes

25 minutes

15 minutes

[12.5 minutes] –

Step 1: Recall the GPS data frame structure.

Step 2: The full almanac is sent in 25 subframes.

Step 3: At a data rate of 50 bps, it takes exactly 12.5 minutes to receive the entire set.

Q22. If an aircraft manoeuvre puts a satellite being used for fixing into the wing shadow then:

the accuracy will be temporarily downgraded

the receiver will automatically select another satellite with no degradation in positional accuracy

the accuracy will be unaffected

the receiver will maintain lock using signals reflected from other parts of the aircraft with a small degrading of positional accuracy

[the accuracy will be temporarily downgraded] –

Step 1: Define signal shadowing.

Step 2: GPS requires line-of-sight; physical blockage (wing/fin) stops the signal.

Step 3: Losing a satellite degrades geometry (higher PDOP), thus downgrading accuracy until a new lock is established.

Q23. In civil aviation, the height value computed by the receiver of the satellite navigation system NAVSTAR/GPS is the:

height above Mean Sea Level (MSL)

geometric height above ground

height above the WGS-84 ellipsoid

flight level

[height above the WGS-84 ellipsoid] –

Step 1: Identify the vertical reference of the GPS coordinate system.

Step 2: GPS computes “geometric height” based on the WGS-84 model.

Step 3: This differs from MSL (Geoid) by a value known as geoid undulation.

Q24. NAVSTAR/GPS operates in the ……. band and the receiver determines position by ……….:

UHF; range position lines

UHF; secondary radar principles

SHF; range position lines

SHF; secondary radar principles

[UHF; range position lines] –

Step 1: Classify GPS frequencies (approx. 1.2-1.5 GHz).

Step 2: 300 MHz to 3 GHz is the UHF (Ultra High Frequency) band.

Step 3: Position is found by measuring distance (range) from multiple satellites to find an intersection.

Q25. The NAVSTAR/ GPS control segment comprises:

a ground segment and the INMARSAT geostationary satellites

the space segment, the user segment and the ground segment

a master control station, a back-up control station, five monitoring stations and the INMARSAT geostationary satellites

a master control station, a back-up control station and five monitoring stations

[a master control station, a back-up control station and five monitoring stations] –

Step 1: Identify the ground infrastructure.

Step 2: The MCS (Colorado Springs) manages the system.

Step 3: Monitoring stations around the globe track satellites and send data back to the MCS.

Q26. The purpose of the pseudo-random noise codes in NAVSTAR/GPS is to:

pass the navigation and system data

pass the almanac data

pass the ephemeris and time information

identify the satellites

[identify the satellites] –

Step 1: Define the function of the PRN code.

Step 2: Every GPS satellite uses the same frequency but different PRN codes (CDMA).

Step 3: The unique PRN allows the receiver to distinguish one satellite’s signal from another.

Q27. The use of LAAS and WAAS remove the errors caused by:

selective availability, satellite ephemeris and clock

receiver clock, PDOP, satellite ephemeris and clock

propagation, selective availability, satellite ephemeris and clock

PDOP, selective availability and propagation

[selective availability, satellite ephemeris and clock] –

Step 1: Identify errors corrected by Differential GPS (DGPS).

Step 2: Reference stations know their exact position and calculate errors in satellite timing/orbit.

Step 3: These systems correct common-mode errors like SA, ephemeris, and satellite clock bias.

Q28. A LAAS requires:

an accurately surveyed site on the aerodrome and a link through the INMARSAT geostationary satellites to pass satellite range corrections to aircraft

an accurately surveyed site on the aerodrome and system known as a pseudolite to pass corrections to X, Y & Z coordinates to aircraft

an accurately surveyed site on the aerodrome and a link through the INMARSAT geostationary satellites to pass corrections to X, Y & Z coordinates to aircraft

an accurately surveyed site on the aerodrome and a system known as a pseudolite to pass satellite range corrections to aircraft

[an accurately surveyed site on the aerodrome and system known as a pseudolite to pass corrections to X, Y & Z coordinates to aircraft] –

Step 1: Define Local Area Augmentation System (LAAS).

Step 2: It is a ground-based system focused on a single airport.

Step 3: It uses local reference receivers and a transmitter (pseudolite) to provide high-precision 3D corrections.

Q29. EGNOS is:

a WAAS

the proposed European satellite navigation system

a LAAS

a system to remove errors caused by the difference between the model of the earth and the actual shape of the earth

[a WAAS] –

Step 1: Classify the European Geostationary Navigation Overlay Service.

Step 2: EGNOS uses geostationary satellites to provide wide-area corrections.

Step 3: It is the European equivalent of the US WAAS (Wide Area Augmentation System).

Q30. The PRN codes are used to:

determine the time interval between the satellite transmission and receipt of the signal at the receiver

pass ephemeris and clock data to the receivers

synchronize the receiver clocks with the satellites clocks

determine the range of the satellites from the receiver

[determine the time interval between the satellite transmission and receipt of the signal at the receiver] –

Step 1: Explain “ranging” via PRN.
Step 2: The receiver generates an identical code and shifts it to match the incoming signal.
Step 3: The amount of “shift” needed tells the receiver exactly how long the signal took to arrive.

Q31. The initial range calculation at the receiver is known as a pseudo-range because it is NOT yet corrected for:

receiver clock errors

receiver and satellite clock errors

receiver and satellite clock errors and ephemeris errors

receiver and satellite clock errors and propagation errors

[receiver clock errors] –

Step 1: Define “Pseudo-range.”

Step 2: It is a raw distance measurement based on the receiver’s internal (non-atomic) clock.

Step 3: Until the time offset (clock error) is solved using a 4th satellite, it is not a true range.

Q32. Which of the following statements concerning NAVSTAR/GPS time is correct?

Satellite time is based on sidereal time

The satellite runs its own time based on seconds and weeks which is correlated with UTC

Satellite time is the same as UTC

The satellite runs its own time based on seconds and weeks which is independent of UTC

[The satellite runs its own time based on seconds and weeks which is correlated with UTC] –

Step 1: Identify the GPS time standard.

Step 2: GPS time counts weeks and seconds since Jan 6, 1980.

Step 3: It is kept very close to UTC but does not include leap seconds.

Q33. Concerning NAVSTAR/GPS orbits, which of the following statements is correct?

The orbits are inclined at 65 deg with an orbital period of 11 hours 15 minutes

The orbits are geostationary to provide global coverage

The inclination of the orbits is 55 deg with an orbital period of 12 hours

The inclination of the orbits is 55 deg with an orbital period of 24 hours

[The inclination of the orbits is 55 deg with an orbital period of 12 hours] –

Step 1: Identify the MEO orbital period.

Step 2: GPS satellites complete one orbit every 11 hours and 58 minutes (approx. 12 hours).

Step 3: The inclination is 55 degrees to the equator.

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