PBN.3.3 PBN Components – Navigation Infrastructure Flashcards
What’s NAVAID infrastructure?
One of the three components of PBN
Refers to Ground and Space-based NAVAIDs
What does it provide?
Positioning capability
What functionality may acft include that can also provide positioning capability?
INS
Which institution sets out performance requirements for nav systems to support the different phases of flight?
ICAO
Where can you find these performance standards?
Annex 10, Volume 1 of the Chicago Convention
What do the navigation aids (NAVAIDs) primarily provide?
Range or bearing information which is received by the acft’s sensors
For what objective is this information used?
To estimate a position
How is this estimate used?
It is compared to a defined flight path by a navigation computer
What are the primary sensors used for Area NAvigation (laterally)
GROUND BASED
VOR/VOR (Bearing/Bearing)
- Requires 2 stations to estimate a position
- Poor accuracy means that it is not used by RNAV systems
VOR/DME (Bearing/Range)
- Angular error from the VOR limits the maximum range for some
navigation applications
DME/DME (Range/Range)
- Requires a minimum of 2 DMEs to estimate a position
- Computer must resolve point of ambiguity (the other point where
the two circles intersect) - Supports all navigation applicaitions down to the Final Approach Fix
(FAF)
SPACE-BASED
- GPS + acft or satellite-based augmentation systems (GNSS)
- 3D position is calculate by estimating range from 4 satellites
What are the systems that support vertical navigation?
(VERTICAL POSITIONING)
- Barometric Altimetry (BARO VNAV)
- Provides readings based on atmospheric pressure (temperature
dependant) - Approach path will become shallower in colder temperatures and
steeper in higher temperatures
- Provides readings based on atmospheric pressure (temperature
- Geometric Altimetry:
- Part of the 3D solution provided by GNSS. Its vertical accuracy is quite good but the integrity of GPS constellation alone is insufficient for aviation approach applications.
What are the systems developed to increase the integrity of the GPS constellation?
- Space Based Augmentation System (SBAS): provides lateral and vertical position accuracy with integrity
- EGNOS - EUROPE
- WAAS - United States
- MSAS - Japan
- GAGAN - India
- SDCM - Russia
- SACCSA South America
- Ground Based Augmentaion Systems (GBAS):
- Supports precision approaches down to CAT I. Could be used by suitably equipped RNAV systems
- Precision Approach is not part of PBN
What are the implications for PBN?
LNAV/VNAV
- Estimated horizontal and vertical position is compared against the defined path created by the nav computer
- Waypoints dfining the path are normally extracted from the nav database
- Lateral and Vertical guidance from the estimated position onto the defined path is called, LNAV and VNAV, respectively
Positioning Accuracy
- Related to the type of navigation sensor used.
- Each sensor has its own error value: Navigation Sensor Error (NSE)
- Also called Dilution of precision (DOP)
What’s DOP dependent on? What is it used for?
Relative angle the signals subtend at the aircraft (angle of cut)
Used by navigation computer to calculate the level of uncertainty in position estimation
Sensors and PBN:
NDB
- Not considered PBN as it is not accurate enough for position estimation
VOR
- The least accurate at long range of the ground-based NAvaids used in PBN
- Too inacurate for the more demaing lateral track accuracy requirements
- VOR only supports RNAV 5
DME
- Supports a navigational performance down to 1NM, providing there are sufficient stations with appropriate geometry
- accuracy of a DME/DME position estimation is too poor when the subtended angles (due to DOP) of the signals from a pair of stations are less than 30º and more than 150º
- DME positions cannot support RNP APCH
GNSS
- Smallest error
- With augmentation (integrity checking) provides a navigation solution for every NAvigation Application
Who decides which sensors are fitted to the aircraft?
The aircraft manufacturers and AOs
On-Board Autonomous Navigation Capability
How can the position information of an aircraft be given by other means than a sensor?
Inertial Platforms
What are the two types of inertial platforms?
Inertial Reference Systems (IRS) & Inertial Navigation Systems (INS)
When is inertial capability required?
Only for the most demanding Navigation Specification - RNP (AR) APCH
Inertial Reference Systems (IRS)
- Positional info derived autonomously, without reference to any external systems and can be used when no other position information is available
- It can provide short term accurate information that can be used with ground or space-based navigation systems to enhance the position estimation.
- It can also be used to replace external sensors to cover short term outages
Where are the limits of IRS prescribed?
In the Navigation Specification, for example:
RNAV 5 - an Inertial platform can be used for 2 hours with no updating, bot for an RNP approach only for 40 seconds
What’s an INS?
A standalone independent systems
From where does it get its inputs?
It is fed from the Inertial Reference Unit (IRU)
Waypoints can be manually entered through the Inertial Navigation Control display (INCDU)
What’s PBN integrity?
Degree of confidence that can be placed on the position estimation by the RNAV system
What will hapen if a flight application using RNP systems fails to meet the integrity requirement?
It will show an alert to the pilot
This will also happen to some RNAV systems including all those using GPS
Why doesn’t the GPS constellation meet the civil aviation integrity requirements?
Because there is the posibility of an undetected satellite failure every 10.000 hours of operation (10^-4)
What’s the civil aviation requirement for integrity and the name of the system developed for this purpose?
One missed detection in 10.000.000 (10^-7) per flight hour aircraft-based augmentation systems
How does ABAS provide integrity monitoring?
Aircraft Autonomous Integrity Monitoring (AAIM) links the GPS receiver to other aircraft systems
- GPS & BARO
- GPS + INS
Receiver Autonomous Integrity Monitoring (RAIM), which compares a series of position estimations within the GPS unit using redundant (extra) satellite signals)
- 4 satellites = 3D position estimate
- 5 satellites = FD
- 6 satellites = FDE
What receivers are capable of Fault Detection (FD)
TSO 129A
What about newer generation receivers?
TSO 196A are able to perform Fault Detection and Exclusion (FDE)
What’s a TSO?
Technical Standard Order, issued by the FAA and stipulates the minimum performance standard for specified materials, parts and appliances used on civil aircraft
What’s the European equivalent?
ETSO (European Technical Standard Order), which is issuedby EASA
How does RAIM provide integrity monitoring?
It is an algorithm integrated in the GPS receiver which compares a series of position estimations for internal consistency
It is based on the availability of additional satellites in view
Using the extra satellite signals, the RAIM algorithm should detect a faulty satellite, known as FD.
If the receiver has extra functionality, it may be able to perform FDE
On what is the availability of integrity monitoring and FDE by RAIM based?
Number of visible, operational satellites
What does FD require?
At least 5 satellites
- If estimated position start to spread out and exceed a preset value, then a fault is declared
What’s the requirement of FDE?
At least 6 satellites
The receiver can detect which satellite is faulty and exclude any positional data received from it
How many satellites most RAIM algorithms assume faulty?
Only one faulty satellite
What’s the probability of the RAIM algorithm failing to detect a faulty satellite?
One time in 1000 (10^-3)
How many seconds can the Use/Don’t use flag take to be received by an aircraft in an SBAS system?
6 seconds
What’s the difference between ABAS and SBAS?
ABAS provide a level of integrity monitoring on board the aircraft
SBAS provide a higher level of integrity by monitoring the GPS constellation and providing use/do not use messages for each satellite in view of the ground system
What’s the greatest use of SBAS?
The provision of a series of correctoins to improve the lateral and vertical accuracy of the position solution
With what specific type of receiver must an aircraft need be fitted?
Aviation certified SBAS receivers to conform with TSO 145A/146A
Within where can the integrity of the GPS signal from monitored satellites be received?
Within the footprint of the Geostationary satellite’s transmission
What does the Geostationary satellite’s transmission cover?
Thewhole of ECAC and beyond
What must the signals-in-space and the aircraft systems meet to meet a specific navigation application?
The required accuracy, integrity and continuity for that operation
What does PBN require aircraft and its systems to be able to do?
Perform for the whole defined operation, as long as it was operating correctly at the start of thath operation
What about the signals from the NAVAIDs?
They should also be available for the required operation and once the particular phase of flight has begun, continue to functoin for the period of that operation
What will the Service Provider need to consider?
How to meet the appropriate requirement for signal availability and continuity.
How is this achieved?
Through redundancy (additional capability to handle failures)
Or by the requirement for the aircraft to carry additional systems (for example, carriage of IRS/IRU)
How must the probability of failure and therefore the unability to complete an operation be?
Acceptably Low
