ATPL - 062.06 LO

062_06.txt

01.01 General
01 State that there are four main GNSSs. These are: USA NAVigation System with Timing and Ranging Global Positioning System (NAVSTAR GPS); Russian GLObal NAvigation Satellite System (GLONASS) ; European Galileo (under construction); Chinese BeiDou (under construction).
02 State that all four systems (will) consist of a constellation of satellites which can be used by a suitably equipped receiver to determine position.

01.02 Operation
01 State that there are currently two modes of operation: standard positioning service (SPS) for civilian users, and precise positioning service (PPS) for authorised users.
02 SPS was originally designed to provide civilian users with a less accurate positioning capability than PPS.
03 Name the three GNSS segments as follows: space segment; control segment; user segment.
04 State that each satellite broadcasts ranging signals on two UHF frequencies: L1 and L2.
05 State that SPS is a positioning and timing service provided on frequency L1.
06 State that PPS uses both frequencies L1 and L2.
07 State that the satellites transmit a coded signal used for ranging, identification (satellite individual PRN code), timing and navigation.
08 State that the navigation message contains: satellite clock correction parameters; Universal Time Coordinated (UTC) parameters ; an ionospheric model; satellite health data.
09 State that an ionospheric model is used to calculate the time delay of the signal travelling through the ionosphere.
10 State that two codes are transmitted on the L1 frequency, namely a coarse acquisition (C/A) code and a precision (P) code. The P code is not used for standard positioning service (SPS).
11 State that satellites are equipped with atomic clocks which allow the system to keep very accurate time reference.
12 State that the control segment comprises: - a master control station- a ground antenna - monitoring stations.
13 State that the control segment provides: monitoring of the constellation status - correction of orbital parameters- navigation data uploading.
14 State that GNSS supplies three-dimensional position fixes and speed data, plus a precise time reference.
15 State that a GNSS receiver is able to determine the distance to a satellite by determining the difference between the time of transmission by the satellite and the time of reception.
16 State that the initial distance calculated to the satellites is called pseudo-range because the difference between the GNSS receiver and the satellite time references initially creates an erroneous range.
17 State that each range defines a sphere with its centre at the satellite.
18 State that there are four unknown parameters (x, y, z and Δt) (receiver clock error) which require the measurement of ranges to four different satellites in order to get the position.
19 State that the GNSS receiver is able to synchronise to the correct time reference when receiving four satellites.
20 State that the receiver is able to calculate aircraft ground speed using the space vehicle (SV) Doppler frequency shift or the change in receiver position over time.
21 Define ‘receiver autonomous integrity monitoring (RAIM)’ as a technique that ensures the integrity of the provided data by redundant measurements.
22 State that RAIM is achieved by consistency checks among range measurements.
23 State that basic RAIM requires five satellites. A sixth one is for isolating a faulty satellite from the navigation solution.
24 State that agreements have been concluded between the appropriate agencies for the compatibility and interoperability by any approved user of NAVSTAR and GLONASS systems.
25 State that the different GNSSs use different data with respect to reference systems, orbital data, and navigation services.

01.03 Errors and Factors Affecting Accuracy
01 List the most significant factors that affect accuracy: ionospheric propagation delay; dilution of position; satellite clock error; satellite orbital variations; multipath.
02 State that a user equivalent range error (UERE) can be computed from all these factors.
03 State that the error from the ionospheric propagation delay (IPD) can be reduced by modelling, using a model of the ionosphere, or can almost be eliminated by using two frequencies.
04 State that ionospheric delay is the most significant error.
05 State that dilution of position arises from the geometry and number of satellites in view. It is called geometric dilution of precision (GDOP).
06 State that the UERE in combination with the geometric dilution of precision (GDOP) allows for an estimation of position accuracy.
07 State that errors in the satellite orbits are due to: solar winds; gravitation of the Sun and the Moon.

02.01 Ground-Based Augmentation Systems (GBASs)
01 Explain the principle of a GBAS: to measure on the ground the errors in the signals transmitted by GNSS satellites and relay the measured errors to the user for correction.
02 State that the ICAO GBAS standard is based on this technique through the use of a data link in the VHF band of ILS–VOR systems (108–118 MHz).
03 State that for a GBAS station the coverage is about 20 NM.
04 State that GBAS provides information for guidance in the terminal area, and for three-dimensional guidance in the final approach segment (FAS) by transmitting the FAS data block.
05 State that one ground station can support all the aircraft subsystems within its coverage providing the aircraft with approach data, corrections and integrity information for GNSS satellites in view via a VHF data broadcast (VDB).
06 State that the minimum software designed coverage area is 10° on either side of the final approach path to a distance between 15 and 20 NM, and 35° on either side of the final approach path up to a distance of 15 NM.
07 State that outside this area the FAS data of GBAS is not used.
08 State that GBAS based on GPS is sometimes called local area augmentation system (LAAS).
09 State that a GBAS-based approach is called GLS approach (GLS-GNSS landing system).

02.02 Satellite-Based Augmentation Systems (SBASs)
01 Explain the principle of an SBAS: to measure on the ground the errors in the signals received from the satellites and transmit differential corrections and integrity messages for navigation satellites.
02 State that the frequency band of the data link is identical to that of the GPS signals.
03 Explain that the use of geostationary satellites enables messages to be broadcast over very wide areas.
04 State that pseudo-range measurements to these geostationary satellites can also be made, as if they were GPS satellites.
05 State that SBAS consists of two elements: ground infrastructure (monitoring and processing stations); communication satellites.
06 State that SBAS allows the implementation of three- dimensional Type A and Type B approaches.
07 State the following examples of SBAS: European Geostationary Navigation Overlay Service (EGNOS) in western Europe and the Mediterranean; wide area augmentation system (WAAS) in the USA ; multi-functional transport satellite (MTSAT)-based augmentation system (MSAS) in Japan ; GPS and geostationary earth orbit augmented navigation (GAGAN) in India.
08 State that SBAS is designed to significantly improve accuracy and integrity.
09 Explain that integrity and safety are improved by alerting SBAS users within 6 seconds if a GPS malfunction occurs.

02.04 Airborne-Based Augmentation Systems (ABASs)
01 Explain the principle of ABAS: to use redundant elements within the GPS constellation (e.g. multiplicity of distance measurements to various satellites) or the combination of GNSS measurements with those of other navigation sensors (such as inertial systems) in order to develop integrity control.
02 State that the type of ABAS using only GNSS information is named receiver autonomous integrity monitoring (RAIM).
03 State that a system using information from additional onboard sensors is named aircraft autonomous integrity monitoring (AAIM).
04 Explain that the typical sensors used are barometric altimeter and inertial reference system (IRS).
05 Define ‘receiver autonomous integrity monitoring’ (RAIM) as a technique that ensures the integrity of the provided data by redundant measurements.
06 State that RAIM is achieved by consistency checks among range measurements.
07 State that basic RAIM requires five satellites. A sixth one is for isolating a faulty satellite from the navigation solution.