Slide Satellite-Based Navigation

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Satellite- Based

Navigation

Muhammad Kemal Aulia S.

Muhammad Arviano Y.

Muhammad Ghaffary A.

Jonwin Fidelis Fam

Hafizh Renanto Akhmad

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Group Members

Muhammad Kemal Aulia Sutadian | 13621016 Muhammad Ghaffary Adreviano | 13621032 Muhammad Arviono Yuono | 1362134

Jonwin Fidelis Fam | 13621051

Hafizh Renanto Akhmad | 13621060

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Introduction to Global Navigation Sys tems

GNSS (Global Navigation Satellite System) is a satellite-based navigation system. The most well-known GNSS is GPS (Global Positioning System), which is operated by the United States, and other GNSS include GLONASS (Russian Global Navigation Satellite System) and Galileo (European system).

GNSS works by measuring the distance between a receiver and multiple satellites, the receiver use the information to calculate its position on Earth.

GNSS is used in a variety of applications, including aircraft navigation and emerging

augmentation systems can be used to increase the accuracy, availability, and integrity of GPS for aircraft navigation.

Muhammad Kemal Sutadian

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18.1 GPS

Overview

GPS (Global Positioning System) is a satellite-based navigation system that was developed by the US military in 1973. The system became fully operational in 1994 and is now widely used for many applications, including aircraft navigation.

The GPS system consists of three segments:

Space segment: 24 satellites in orbit around the Earth

User segment: GPS receivers, such as those found in aircraft

Control segment: A network of ground stations that monitor and control the satellites

The principles of satellite navigation are based on radio wave propagation, precision timing and knowledge of each satellite’s position above the earth; this is all monitored and controlled by a network of stations

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18.2 Wave

Propagation Pr inciples

Satellite navigation works by measuring the time delay between when a radio signal is transmitted from a satellite and received by an observer on the Earth's surface and the time delay is used to calculate the distance between the satellite and the observer.

In the case of satellite navigation, the radio signals travel at the speed of light from the satellite to the observer. The observer can use the time delay to

calculate its distance from the satellite and measuring the time delay to multiple satellites, the observer can calculate its position on Earth.

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18.3 Satellite

Navigation Prin ciples

The property of wave propagation that can be used for satellite navigation purposes is the time delay between when a radio signal is transmitted from a satellite and received by an observer on the Earth's surface and the time delay is used to calculate the distance between the satellite and the observer.

To calculate a position on Earth using satellite navigation, the observer needs to measure the time delay between receiving radio signals from at least four satellites, due to each satellite can only provide a distance measurement,

which is not enough to uniquely identify a position on a sphere.

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By measuring the time delay to four satellites, the observer can calculate its position in three dimensions (latitude, longitude, and altitude) and the accuracy of the system

depends on having good visibility of the satellites.

Once the observer's position has been calculated, the GPS receiver can derive other useful navigation information, such as track, ground speed, and drift angle.

In short, the following are the steps in satellite navigation:

The observer measures the time delay between receiving radio signals from at least four satellites.

1.

The observer uses the time delay measurements to calculate its distance from each satellite.

2.

The observer uses the distances to the satellites to calculate its position in three dimensions.

3.

The GPS receiver uses the observer's position to calculate other useful navigation information.

4.

18.3 Satellite Navigation

Principles

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Muhammad Arviano Yuono

Muhammad Arviano Yuono | AE4020

S p a c e

G r o u n d ( C o n t r o l ) U s e r

18.4 GPS Segm ents

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17 ft (5.2 m)

2000 lb (907 kg)

~ 52000 km

18.4 GPS Segm ents

Space

segment

Orbit :

10,900 nm (approx. 20,200 km) above the earth.

optimum ground coverage, minimum amount of satellites.

Orbits the earth twice a day.

55° incline with respect to the equatorial plane.

Six orbits with 4 satellites each.

minimum of five satellites should be in view to a receiver located almost anywhere on the earth’s surface.

There are 24-29 satellites in use (operational and backups).

Installed with 4 atomic clocks (accuracy of 3 nanoseconds/day) with 4 back up clocks.

Solar powered with nickel cadmium battery as electrical power back up.

Operational life of 5-10 years.

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18.4 GPS Segm ents

Space

segment

Satellites also download almanac data, a set of orbital parameters status for all satellites in the constellation.

The receiver uses almanac data during initial acquisition of satellite signals.

Ephemerides/ ephemeris data is also downlinked by each satellite; this data contains current satellite position and timing information.

Almanac Data

Ephemeris Data

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Schriever Air Force Base,

Colorado Springs, USA.

Hawaii

Ascension

Diego Garcia

Kwajalein

Master Control Station (MCS) Monitoring Station

Ground Antennas

18.4 GPS Segm ents

Ground

segment

Monitor Station

The locations of the monitoring stations provide ground visibility for each satellite.

Tracks all satellites in view; ranging data and satellite health information is collected on a continuous basis.

Master Control Station

Monitors and mathematically synchronizes satellite clocks relative to Coordinated Universal Time (UTC).

Processes data from Monitor Station to establish precise orbits and update satellite ephemeris data.

Ground Antennas

Transmits updated data to each satellite.

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5'’

7'’

18.4 GPS Segm ents

User

segment

GPS

Satellites that are less than 5° from the horizon are rejected as an inherent feature of the antenna’s design. Other design features include the ability to reject signals that are reflected, e.g. from the sea by rejecting incorrectly polarised signals. The antennas receive signals directly from whichever GPS satellites are within line of sight. GPS Reciever contains RE filters, a quartz clock (to reduce equipment costs versus atomic clocks) and a processor.

How it works ?

The receiver and satellite generate identical pulse coded signals at precisely the same time (Figure 18.7); these signals are compared in the receiver to provide the basis of time delay (At) measurements. When the time delay from the satellite has been measured, it is compared with the known position and orbit ofthe satellite. This calculation provides a first line of position (LOP). Acquiring second and third satellites provides a unique position as previously described; however, the receiver needs to take into account its clock error (bias)

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Time Error

Since the receiver’s quartz clock is not as accurate as the each satellite’s atomic clock, the clock error (bias) can be anticipated in the range calculations from four satellites. The time bias error means that the first LOP is not the true range; the calculated range is therefore a pseudorange (Figure 18.8), defined as true range ± the range associated with clock error. (Every microsecond of clock error represents a range of 300 metres.) Since the individual receiver’s clock error is the same with respect to any satellite, using four satellites defines a precise and unique position as illustrated in Figure 18.9. Note that, since the satellites are in the order of 11,000 nm from the receiver, and are all in different orbits, we need to know the exact position of each satellite via its ephemeris data (transmitted as part of the message code).

18.4 GPS Segm ents

User

segment

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18.5 GPS Signa ls

GPS satellites transmit signals at low power using two carrier frequencies, L1 (1575.42 MHz) and L2

(1227.60 MHz). This dual-frequency transmission allows for the comparison of signal refraction through the ionosphere and the application of necessary corrections. The carrier frequencies are modulated with pseudorandom codes, which are complex digital codes resembling random electrical noise and are

essential components of GPS. There are three sets of data to be modulated on the L1 and L2 carrier waves:

Course acquisition (C/A) code Precise (or protected) P-code Navigation /system data

The coarse acquisition (C/A) code is a digital sequence used by commercial GPS receivers to determine satellite range. It modulates the carrier wave at 1.023 MHz and repeats every 1 ms. The P-code, available to the military, is modulated on both L1 and L2 carriers at 10.23 MHz and can be encrypted as a Y-code for

security. Data exchange between satellites and monitoring stations occurs using uplink and downlink frequencies in the S-band (2227.5 and 1783.74 MHz).

Muhammad Ghaffary Adreviano

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18.6 GNSS Operation

GNSS operation depends on the number of satellites in view. Three satellites provide a 2D position fix, while four or more are ideal for navigation. The receiver typically takes 15-45 seconds to acquire signals from at least four satellites for navigation. It can speed up the process with an initial position fix from the inertial reference system. In cases of poor satellite coverage for brief periods, other navigation sensors are used for dead reckoning. If satellite

reception remains poor for a while, the system re-enters the

acquisition mode.

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18.6 GNSS Operation

Selective

availability

Selective availability (SA) was a feature of GPS that intentionally introduced errors (typically 10 metres horizontally, and 30 metres vertically) into the publicly available L1 signals. This was a political strategy at the time that denied any advantage for

hostile forces acting against the USA.

The highest GPS accuracy was available (in an encrypted form) for the US military, its allies and US government users. During the 1990s, a number of political factors were mounting in the USA including a shortage of military standard GPS units

during the 1990s Gulf War; the widespread availability of civilian products; the FAA’s long-term desire to replace ground based radio navigation aids with GPS.

This led to a presidential decision in 2000 allowing all users access to the L1 signal

without the intentional errors.

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18.6 GNSS Operation

Vulnerability

GNSS signals are vulnerable to interference due to their weak reception, potentially affecting a wide area. While conventional radio navigation aids can also be

disrupted, GNSS serves more aircraft simultaneously, making interference a significant concern. Interference, including atmospheric effects, can lead to

navigation errors, especially when satellites are not well visible or have suboptimal geometry.

Accuracy depends on precise ephemeris data about each satellite's position.

Various external factors, such as multi-path errors from signal reflections, atmospheric conditions, and ionospheric effects, can introduce errors, but correction factors can be applied in some cases. The use of two transmitted

frequencies (L1 and L2) allows for the comparison of signal travel times, aiding in

error correction.

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18.6 GNSS Operation

Vulnerability

Calculating ranges accuracy, whether from satellites or ground navigation aids, depend on optimal

geometry. When the angle between two satellites viewed by the receiver is acute, it results in an inaccurate position fix. In satellite navigation, this situation is known as geometric dilution of precision (GDOP). The

GDOP is greater when two satellites are closer together from the perspective of the aircraft. This dilution of precision (DOP) can be broken down into specific components:

PDOP (position DOP based on geometry only) HDOP (horizontal contribution to PDOP)

VDOP (vertical contribution to DOP) TDOP (range equivalent of clock bias)

Receiver almanac data and satellite ephemeris data work together to help the receiver find specific satellites for the best geometry. The errors discussed so far are unintentional, but there is a continual

concern about deliberate interference called 'spoofing,' which is an intentional disruption of GNSS signals.

Aviation authorities are actively testing GNSS signal quality and developing strategies to counteract these threats.

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18.6 GNSS Ope ration

Jonwin Fidelis Fam

Integration

GNSS Equipment can be used in isolation or with other avionic systems to provide different levels of operation.

For example, in general aviation (GA), GNSS receivers are often integrated with ILS–VOR and VHF communication systems. This example is a self- contained, panel-mounted device. Graphics are used to provide a multifunction-type display; the text is displayed on the screen for selected frequencies, distances, bearings, etc.

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18.6 GNSS Ope ration

Jonwin Fidelis Fam

Integration

GNSS can also be integrated with INS to complement each other’s properties.

There are three techniques, those being loosely coupled, tightly coupled and deeply coupled.

Loosely coupled; the difference between position and velocity measurements obtained by GNSS and INS is used.

Tightly coupled; the difference between the pseudorange, carrier phase or Doppler Shift measurements

Deeply coupled; INS and GNSS are not independent

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EGNOS (European Geostationary Navigation Overlay Service)

Developed by the European Space Agency (ESA); precursor to Galileo

Currently supplements GPS on accuracy and reliability, will supplement Galileo in a future version

Consists of:

40 Ranging Integrity Monitoring Stations

2 Mission Control Centres

6 Navigation Land Earth Stations EGNOS Wide Area Network

3 geostationary satellites

18.7 GNSS Evol ution

Jonwin Fidelis Fam

European GNSS

Inmarsat 3 Satellite

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18.7 GNSS Evol ution

Jonwin Fidelis Fam

European GNSS

Galileo

European system created by European Space Agency (ESA), operated by the European Union Agency for the Space Programme (EUSPA)

Aims to provide an independent high-precision positioning system; do not have to rely US GPS or Russian GLONASS

Early Operational Capability (EOC) on 15 December 2016, Full Operational Capability (FOC) in 2020.

Providing

Open Service (OS); simple timing down to 1m

High Accuracy Service (HAS); up to 20cm free of charge

Public Regulated Service; anti-jamming and reliable problem detection (for government bodies)

Search and Rescue (SAR) function based on Cospas-Sarsat system.

Horizontal and vertical position measurements within 1m precision

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Galileo

Space Segment

30 in-orbit spacecraft (24 in full service, 6 spares) lifetime: >12 years

altitude: 23,222 km (MEO)

3 orbital planes (each 8 operational and 2 active spares)

Ground Segment

2 Ground Control centres for Satellite and Mission Control

7 Telemetry, tracking & control (TT&C) stations 10 mission data uplink station (ULS), 2 per site 1 service centre

several GSS (sensor stations) data dissemination network Signal

18.7 GNSS Evol ution

Jonwin Fidelis Fam

European

GNSS

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Jonwin Fidelis Fam

Russian GNSS

GLONASS

Russian system created by Soviet Union, operated by Roscosmos (Russia) Alternative of GPS

Began in 1976, completion in 1995, full coverage on Russia by 2010, and full global coverage by October 2011, GLONASS-K2 enter service in 2023 Providing

Open Service (OS); simple timing down to 1m

High Accuracy Service (HAS); up to 20cm free of charge

Public Regulated Service; anti-jamming and reliable problem detection (for government bodies)

Search and Rescue (SAR) function based on Cospas-Sarsat system.

Horizontal and vertical position measurements within 1m precision

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GLONASS

Space Segment

24 in-orbit spacecraft (18 for Russia) altitude: 19,100 km (MEO)

3 high latitude orbital planes (where GPS can be problematic)

Ground Segment

a system control centre

5 Telemetry, Tracking and Command Centres 2 Laser Ranging Stations

10 Monitoring and Measuring Stations Signal

open standard-precision signal L1OF/L2OF and obfuscated high precision signal L1SF/L2SF

18.7 GNSS Evol ution

Jonwin Fidelis Fam

Russian

GNSS

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Jonwin Fidelis Fam

Chinese GNSS

BeiDou

Created by China, operated by China National Space Administration (CNSA)

Alternative of GPS

BeiDou-1 in 2000 for limited coverage and navigation services, decommissioned at 2012, BeiDou-2 operational in December 2011, service to Asia-Pacific, BeiDou-3 for global coverage finished 2020

Providing

BeiDou-1 (disaster area [2008 Sichuan Earthquate] information and border guards)

BeiDou-2 (services to Asia-Pacific [55-180 E and 55 S to 55 N]) BeiDou-3 (global coverage)

BeiDou-2 is more accurate than GPS within the area, BeiDou-3 claim to reach mm-level accuracy

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BeiDou

Space Segment

(BeiDou-1) 4 geostationary orbit satellites

(BeiDou-2) 35 satellites (5 geostationary , 30 non- geostationary [27 MEO and 3 geosynchronous])

(BeiDou-3) 3 GEO satellites, 3 IGSO sattelite, 24 MEO satellites

Signal and Accuracy

(BeiDou-1) 2,491.75 MHz, accuracy 20m (100m uncalibrated) (BeiDou-2) 4 Bands [E1, E2, E5B, and E6], accuracy 10 m (free) and 10cm (military)

(BeiDou-3) B1C/B1I/B1A (1575.42 MHz), B2a/B2b (1191.79 MHz), B3I/B3Q/B3A (1268.52 MHz), and B test frequency (2492.02 MHz)

Jonwin Fidelis Fam

Chinese GNSS

Around the Earth, Polar view and Earth Fixed Frame - equatorial view front and side

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QZSS (Quazi-Zenith Satellite System)

Owned by the Japanese Aerospace Exploration Agency (JAXA)

Enhance GPS in the Asia-Oceania regions, especially in Japan

Consists of 4 satellites (1 November 2018) [1 geostationary and 3 Tundra-type]); 7 satellites (independent of GPS), 11 expansion in May 2023 Services:

PNT (Positioning, Navigation and Timing) SLAS (Sub-metre Level Augmentation) CLAS (cm Level Augmentation)

MADOCA-PPP (Multi-GNSS Advanced Orbit and Clock Augmentation - Precise Point Positioning)

DC Report (Disaster and Crisis Management) PTV (Positioning Technology Verification)

Q-ANPI (QZSS Safety Confirmation Service) - short message service

18.7 GNSS Evol ution

Jonwin Fidelis Fam

Other GNSS

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IRNSS (Indian Regional Navigation Satellite System)

Owned by the Indian Space Research Organization

Currently an RNSS, planning to be GNSS in the near future Accurate position information service in India

Consists of 7 satellites ( 3 GEO and 4 IGSO), expansion until 24 satellites TBD.

Services:

Standard Positioning Service (SPS) - all users Restricted Service - authorized users

Accuracy to 20m

Terrestrial, Aerial and Marine Navigation

Disaster Management; Vehicle tracking and fleet management; Integration with mobile phones; Precise Timing; Mapping and Geodetic data capture; Terrestrial navigation aid for hikers and travellers; Visual and voice navigation for drivers

18.7 GNSS Evol ution

Jonwin Fidelis Fam

Other GNSS

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18.8

GNSS Augment ation

To meet ICAO performance requirements for en route, terminal, approach, and landings, GNSS

constellations require augmention systems. These augmentations can be implemented in form of:

Aircraft-based augmentation system (ABAS), 1.

Satellite-based augmentation system (SBAS), and 2.

Ground-based augmentation system (GBAS).

3.

ABAS

on-board avionics implementation

processes GNSS signals to achieve the accuracy and integrity required to support en route, terminal, and non-precision approach (NPA) operations.

SBAS

uses a network of ground reference stations and geostationary earth orbit (GEO) satellites used to augment en route navigation and approaches with vertical guidance

Hafizh Renanto Akhmad | AE4020

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18.8

GNSS Augment ation

(condt’) SBAS

in geograhic regions has the potential to support seamless guidance where their service areas overlap:

WAAS: USA Wide Area Augmentation System

EGNOS: European Geostationary Navigation Overlay Service MTSAT: Japan MTSAT Satellite Augmenatation System

GAGAN: GPS and GEO Augmented Navigation System

SDCM: Russia System for Differential Correction and Monitoring

GBAS

uses airport monitoring stations to process signals fom GNSS constellations and broadcast corrections and approach path data

used to support precision approach and landing operations

also has the potential to support surface movement operations.

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18.8.1

Error Detection

A GNSS receiver can be installed with error detection software, known as receiver autonomous integrity monitoring (RAIM).

The monitoring process is achieved by comparing the range estimates made from five satellites.

RAIM

performs a consistensy check on all tracked satellites.

ennsures that the available satellite geometry allows the receiver to calculate a position within a protection limit:

Oceanic: 4 nm En route: 2nm Terminal: 1 nm

Non-precision approaches: 0.3 nm

During oceanic, en route, and terminal phases, RAIm is avaiable nearly 100% of the time.

RAIM

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18.8.1

Error Detection

(condt’) RAIM

The predictions function indicates whether RAIM is available at a specific date and time.

Computations predict satellite coverage within ±15 minutes of the specified arrival date and time.

As approaches has a tighter protection limit, there may be times when RAIM is not available.

RAIM prediction must be initiated manually if there is a concern over SBAS/WAAS coverage at the destination or some other reason that compromises navigation precision.

If RAIM is not predicted to be available for the final approach course, the approach does not become active.

If RAIM is not available when crossing the final approach fix (FAF), the missed approach procedure must be flown.

RAIM

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Barometric aiding (‘baro-aiding’)

an integrity augmentation process whereby the GPS uses a non- satellite input source (e.g. the aircraft’s pitotstatic system) to provide vertical reference, thereby reducing the number of required satellites from five to four.

requires four satellites and a barometric altimeter input to detect an integrity anomaly.

Barometric vertical navigation (‘baro-VNAV’) uses barometric altitude information from the aircraft’s pitot-static system and air data computer to compute vertical guidance for the pilot. The specified vertical path is typically computed between two waypoints or an angle from a single waypoint.

18.8.1 Error Detection

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Failed satellite(s) can be dealt with fault detection and exclusion (FDE): failed satellite(s) can be excluded from the GPS range estimates by comparing the data from six satellites.

Aircraft typically carry dual systems:

operators perform pre-flight predictions to ensure that there will be enough satellites in view to support the planned flight.

This provides operators with a cost-effective alternative to inertial navigation systems in oceanic and remote airspace.

18.8.1 Error Detection

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LPV (Localizer Performance with Vertical guidance) approaches in Europe utilise SBAS/EGNOS for improved accuracy, integrity, continuity and availability.

This is achieved by measurements from reference stations; errors are then transferred to a computing centre, which calculates differential corrections and integrity messages.

These messages are broadcast via geostationary satellites as an augmentation or overlay of the original GNSS message.

LPV provides lateral and vertical guidance to provide an approach very similar to a Category I ILS. Also, same with ILS, LPV has vertical guidance and is flown to a Decision Altitude (DA).

18.8.2 Augmented

Approaches

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The standard 3° glide slope of ILS can’t always be used for airports surrounded by mountains. Certain airports are approved for ‘steep approach’, using 4.5°-5.5° degrees pesudo glide slope based on GPD coordinates

18.8.3 Steep

Approach

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PinS are an approach procedure that includes both an instrument and a visual segment. PinS are being developed and introduced for helicopters.

18.8.4 Point in Space

(PinS)

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18.8.4 Point in Space (PinS)

Approaches are flown from the final approach fix (FAF) up to the PiNS PinS also serves as missed approach point (MAPt)

From the point, pilot can elect fo fly to the final segment (tujuan akhir), e.g., to a helipad on a roof of a bulding, or initiate a missed approach.

PinS approach’s main benefit is the flexibility of selecting the MAPt.

PinS Approach

MAPt

That point in an instrument approach procedure at or before which the prescribed missed approach procedure must be initiated in order to ensure that the minimum obstacle clearance is not

infringed

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18.9

Future of GNSS

There’s a long-term (about 10 years) intention of the aviation community to rationalise the air traffic management through increased use of GNSS.

will be realised with the various augmentation systems discussed earlier and additional GNSS constellations.

What will happen to other navigation aids?

There are programmes in place to eventually replace ADF and VOR.

DME aids will be retained for a longer period to optimis the existing network in support of PBN.

ILS/MLS will still be used for automatic approach and landing with GNSS to mitigate for satellite outage or disruption.