Mankind's Dream of Flying
Man has always wanted to fly. It is believed since he saw the birds flying. Many attempts have been made and in many different ways, but all have failed.
From the 17th century until the 20th century much has been done. Imitations of birds attached by a cable, wings for men, similar to those of birds, to be flapped like birds. Balloons that later evolved into airships, gliders and small flying machines that would evolve to be airplanes. Up to the modern planes we have today. In the last decade, the UAV – Unmanned Aerial Vehicle is being developed very fast.
Many old and traditional applications are being substituted by the UAV; the electric power transmission line maintenance is one excellent example. There are many companies using UAVs for routine maintenance and repair of the electric power line transmission with lower cost and less human risk.
It is not my intention to show the History of Aviation here. I bring only a small timeline of Aviation for us to be in tune with some important things we will see in this blog.
The "Golden Age of Aviation" (1918 - 1939)
During the years between World War, I and World War II (interwar period), aircraft technology, in general, has developed a lot. In this period, rapid advances were made in the design of airplanes and airlines started to operate. It was also a time when airmen began to impress the world with their achievements and skills.
The existing aircraft had their main material, wood, replaced by aluminium. Aircraft engines have been greatly improved, with a noticeable increase in power compared to what engines at the time could generate.
This great series of technological advances, as well as the growing socio-economic impact that airplanes have had worldwide, makes this period the golden age of aviation.
The Future
Since the early 1990s, commercial aviation has developed technologies that have made the airplane increasingly automated, thus gradually reducing the importance of the pilot in the operation of the aircraft, with a view to reducing air accidents caused by human error.
Commercial aircraft manufacturers continue to research ways to improve airplanes, making them increasingly safe, efficient and quiet. At the same time, pilots, airspace controllers and mechanics have become increasingly well-trained, and aircraft are, more each time, being surveyed to avoid accidents caused by human or mechanical failure.
History: Foundation of the International Civil Aviation Organization (ICAO)
The consequence of the studies initiated by the US and subsequent consultations between the Major Allies was that the US government extended an invitation to 55 States or authorities to attend, in November 1944, an International Civil Aviation Conference in Chicago.
Fifty-four States attended this Conference, at the end of which a Convention on International Civil Aviation was signed by 32 States, setting up the permanent International Civil Aviation Organization (ICAO) to secure international co-operation and the highest possible degree of uniformity in regulations and standards, procedures and organisation regarding civil aviation matters.
At the same time, the International Services Transit Agreement and the International Air Transport Agreement were signed.
The most important work accomplished by the Chicago Conference was in the technical field because the Conference laid the foundation for a set of rules and regulations regarding air navigation as a whole, which brought safety in flying a great step forward and paved the way for the application of a common air navigation system throughout the world.
Since the beginning of aviation and commercial exploration, the world-class organizations have had one concern in mind: "How to fly safer". Several civil organizations all over the world were created to develop standardization and regulations for safety in aviation.
In addition, several local branches in every country were created to manage the investigations of aviation accidents and incidents. After many years of investigating several accidents, they concluded that an accident is a result of several errors and problems.
Today ICAO has several books, that are periodically revised, to be followed by anyone that wants to work in the Aviation market. Here are the items published by ICAO:
- Personnel Licensing
- Rules of the Air
- Meteorological Service
- Aeronautical Charts
- Units of Measurement to be used in Air and Ground Operations
- Operation of Aircraft
- Aircraft Nationality and Registration Marks
- Airworthiness of Aircraft
- Aeronautical Telecommunications
- Air Traffic Control Service, Flight Information Service and Alerting Service
- Aircraft Accident and Incident Investigation
- Aerodromes Design and Operations
- Aeronautical Information Services
- Security
- The Safe Transport of Dangerous Good by Air
If a new subject is created, ICAO will include wisely to the pertinent item or create a new one if necessary.
The CNS-ATM (Communication, Navigation, Surveillance, Air Traffic Management) has published the Book 9750_2ed_en containing the Global Air Navigation Plan for CNS/ATM Systems.
CNS-ATM
In the early 1980s, ICAO was monitoring the growth in the number of flights. In 1983 a special committee was created for Future Air Navigation Systems - FANS. Over the years this committee has established a modus operandi called CNS-ATM Communication Navigation Surveillance - Air Traffic Management.
The implementation of the CNS-ATM would be long, too long. As new standards were written, new systems were being developed and certified to be operational.
In addition to the growth of numbers of flights, there was the need of making the flights safer and with fewer risks, concerning the separation of the aircraft. So began the studies to make it possible with the CNS-ATM implementation.
During this blog, we will understand better and with certainty, it would be necessary to change the old ways of communication, navigation, surveillance and ATM to achieve this target. These are the basic requirements to increase the number of flights, reduce aircraft separation and have fewer risks and safer operations. Other reasons I will mention later when I explain about CNS-ATM.
The next figure will give us an idea of the several phases of a flight. I will show another figure, on the CNS-ATM part, to give us an idea of the future system.
The next figure illustrates the basic difference of the navigation based on conventional NAVAIDs, RNAV and RNP. The figure shows RNAV and RNP two navigation methods where the pilots set the destination and the departure points, different from the conventional flight plan route. This is part of Navigation of the CNS-ATM.
Surveillance - Automatic digital transmission of the aircraft's location by a data link, for example, ADS-B (Automatic Dependent Surveillance-Broadcast), ADS-C (Automatic Dependent Surveillance–Contract) and MLAT (Multilateration). ADS-B and MLAT need two blogs to explain how it works, coming next.
The last two figures gave us the idea that was about to change. From the conventional navigation based on ground equipment to the RNAV (ARea Navigation) and to RNP (Required Navigation Performance).
We can deduce that the flight from the departure to the destination place changed. RNAV reduced the duration flight, the consequence is less fuel. The RNP flights reduced the lateral separation of the aircraft. So now we may understand the need for new systems to reduce the risks and flying safer, all to be implemented on CNS-ATM.
The Need for CNS-ATM
The CNS-ATM should contemplate the solution of some issues such as traffic congestion, delays, absence of cover in oceanic areas and/or remote, more optimized routes, with more precision, better procedures, and failures in radio communications, all aiming at more efficiency and safety.
The next figure gives us some equipment used before the CNS-ATM concept. Some of the equipment still will be used on the new concept. Some equipment with upgrades of hardware, software and functionality.
Now it is time to know a little about the equipment in the figure above and some others.
Let´s explore it, the systems before the CNS-ATM.
Communications
VHF (Very High Frequency) and HF (High Frequency) radio. The VHF radio has a limited coverage area. For this reason, it is necessary to plan where it shall be implemented, that is, in the places where there are air routes and differences in the levels where there is an airway. This should be overcome in the new concept.
The HF radio signal is received in very distant places by the reflection of the signal in the ionosphere. The quality of the signal leaves something to be desired, suffering a lot of interference and the quality of the audio is very poor.
Navigation
Navaids is basically - VOR-DME (VHF Omnidirectional Radio Range - Distance Measuring Equipment), DVOR (Doppler VHF Omnidirectional Radio Range), ILS (Instrument Landing System) and MLS (Microwave Landing System).
I only mentioned MLS for us to know that ILS is not the only way of landing with all kinds of weather. As far as I know, MLS is no longer used.
Surveillance
The position of the aircraft informed by pilots, Primary Surveillance Radar (PSR) and Secondary Surveillance Radar (SSR).
The principle of operation of the PSR is very simple. A signal is transmitted in all directions and when the signal returns, after being reflected by an aircraft, the time between the aircraft and the radar is used to calculate its position. The radar is called primary radar. The aircraft do not need any equipment.
The SSR systems consist of two main elements, a ground-based interrogator/receiver and an aircraft transponder. The aircraft’s transponder responds to interrogations from the ground station, enabling the aircraft’s range and bearing from the ground station to be determined.
SSRs which relies on targets being equipped with a transponder also requests additional information from the aircraft - such as its identity and altitude. The code gives the plane's identity and radar stations go on to establish speed and direction by monitoring successive transmissions.
Both radars require installation, the SSR requires equipment embedded in the aircraft to exchange information with the SSR ground equipment.
Usually, the two systems are installed together on the terrestrial infrastructure.
ATM - Air Traffic Management
ATC - Air Traffic Control services on airways and terminals with limited data processing.
To ensure that we have the ability to monitor and control more air movements, the aircraft with reduced separation, with the same level security or even safer, we need new methods and new technologies.
Today we have the CNS-ATM system operational, but not fully implemented all around the world, only in some places are there still some features to be implemented.
CNS-ATM in More Detail
I would like to remind you that CNS-ATM is a complex subject. It took a lot of time and plenty of specialists all over the world to do it. It is still being upgraded - the conception. It was implemented in some countries but not with the full version, this is done as planned by ICAO.
We should understand that air traffic is not supposed to stop during implementation. The new system should operate in parallel as a test, during the implementation, and only begins full operation after a period of parallel testing.
Note: Considering the complexity of the CNS-ATM subject my wish is only to give an overview of it. Certainly, this Blog may not be complete to cover the entire CNS-ATM specification, but just introduce some essential changes and the new systems that were thought of to make it possible to be operational.
Now it is time to talk about CNS-ATM and the main differences compared to the old systems. Some of the equipment used will be a new concept, with upgrades of hardware, software and functionality. As I explained previously, not only the increasing numbers of flights were the only reasons to think about CNS-ATM, but to have skies without borders, direct routes, control flexibility, increased security and better use of the aircraft capacity.
The next figure we have seen before but only with the interest of understanding the several phases of flight. Here I will show the new ideas of the CNS-ATM.
- Take-off
- Moving Map, Ground Vehicles and Runway Incursion
- Departure
- RNAV
- Cruise
- RVSM, RNAV/RNP, SBAS (Satellite Based Augmentation System), CPDLC (Control Pilot Data Link Channel) and ADS
- Metering/ Descent and Approach
- Terminal Area, Convergent and ADS
- Landing and All-Weather Approaches
- Landing with all-weather
Summary of CNS-ATM Systems
First, I would like to say that the implementation should be very carefully planned, following the ICAO´s recommendations and according to the country. Some systems should require installation on the aircraft and others on the aerodromes.
Communication - Digital communication by data and voice link between aircraft and the flight controller at the ground station.
- CPDLC (Control Pilot Data Link Channel) is a way to eliminate the inconvenience of voice communication. There is an exchange of information that was pre-recorded and essential, avoiding misunderstandings. Other systems are being used
- ACARS (Aircraft Communications, Addressing and Reporting System)
- SATCOM (Airborne radiotelephone communication via a satellite)
- VDL (VHF Digital Link)
The next figure shows the basic difference considering the use of CPDLC and we may notice that HF Radio is not on the communications using satellite. The aircraft has the HF Radio and if a problem occurs with the satellite communications it will be used if the aircraft is out of the VHF cover range.
CPDLC has several pre-recorded messages to facilitate the communications between the ATC (Air Traffic Controllers) and the Pilots.
Communications before CNS-ATM then
Communications after CNS-ATM (CPDLC detailed)
Navigation - Air navigation, without a doubt, is the most innovative of CNS-ATM. It allows for a smaller distance between aircraft with all the required security, fuel economy by programming the destination and departure points.
GNSS (Global Navigation Satellite Systems) allows for a smaller distance between aircraft with all the required security. Greater fuel economy by programming the destination and departure points. The GNSS used here allows this.
I have written a Blog about GNSS. It is completely changing the Navigation systems. The advantage goes from programming the flight up to the precision of it. For us to understand this I think the best way is a specific blog about the subject.
RNAV (Area Navigation) is a method of navigation which permits the operation of an aircraft on any desired flight path; it allows its position to be continuously determined wherever it is rather than only along tracks between individual ground navigation aids.
RNP (Required Navigation Performance) is similar to Area Navigation (RNAV), but RNP requires on-board navigation performance monitoring and alerting capability to ensure that the aircraft stays within a specific containment area.
An illustrative example of an imaginary duct in which the aircraft ideally flies in the RNP.
RVSM (Reduced Vertical Separation Minima or Minimum) is the reduction to acceptable levels.
Note: the next figure gives us an idea of the vertical and in-trail separation yesterday and today. We may imagine that the new system should guarantee flights with fewer risks and with lower separation.
Surveillance
ADS - Automatic Dependent Surveillance allows the aircraft to transmit extremely relevant automatic flight data. Several surveillance equipment are used.
Mode S enhanced surveillance is a combined secondary surveillance radar (beacon) and ground-air-ground data link system. This technology can improve the quality of aircraft detection, identification and altitude reporting information.
A transponder (XPDR) is a receiver/transmitter which will generate a reply signal upon proper interrogation; the interrogation and reply being on different frequencies by ICAO.
ADS-B (Automatic Dependent Surveillance-Broadcast) - is a system that uses transmissions from aircraft to provide geographical position, pressure/altitude data, positional integrity measurements, flight identity, 24-bit aircraft address, velocity and other data which have been determined by airborne sensors. It should be equipped with aircraft avionics.
ADS-C (Automatic Dependent Surveillance – Contract) - is also known as Automatic Dependent Surveillance – Addressed (ADS-A) or simply Automatic Dependent Surveillance (ADS). With ADS-C the aircraft uses onboard navigation systems to determine its position, velocity, other data and reports this information to the responsible air traffic control centre.
Information that may be sent in ADS-C reports includes present position (latitude, longitude, altitude, timestamp and FOM - Flight Operations Manual), Predicted route in terms of next and (next + 1) waypoints, velocity (ground or air referenced) and meteorological data (wind speed, wind direction, and temperature).
The figure from the FAA site shows in a simple way the ADS-B way of working. What is not written is that there is no shadow anymore, concerning the mountains and oceanic travel.
ATM - Air Traffic Management
ATC - Air Traffic Control services on airways and terminals with limited data processing. There are limitations to the amount of traffic that ATC systems can handle, this includes the traffic on the aerodrome, without increasing levels of automation to assist with conflict detection and resolution.
For these reasons, aircraft must plan their flights along with ATS – Air Traffic Services routes and be channelled, to a certain degree, in order for ATC to keep aircraft safely separated from each other.
With new technologies that are being used in air navigation, new procedures, new routes, new charts SIDs (Standard Instrument Departure), STARs (Standard Terminal Arrival) and integrated aviation control systems, the ATM should be improved to support higher numbers of flights, with reduced separation and using fewer human resources in a safer way. ATM efficient and flexible air traffic management at all levels of flight, including in remote and ocean areas and with high data processing.
Final Considerations
CNS-ATM puts together satellite and digital communications, PBN and ADS-B.
The advantages of modern CNS-ATM systems are that they are global, high bandwidth and accurate.
The use of satellite navigation systems where the user performs on-board position determination from satellite information has been adopted as GNSS.
When CNS-ATM was being written there was an expectation that the landing will use GNSS, called GBAS – Ground-Based Augmentation Systems, would be used all over the world. But countries with the same location in relation to the equator cause delay of the GPS signal. The mitigation of this problem is being studied. Up to now, the GBAS systems are not allowed to be used for landings all over the world.
Note: As a GPS signal passes through the charged particles of the ionosphere and then through the water vapour in the troposphere, it gets slowed down a bit, and this creates the same kind of error as bad clocks. The ionosphere is the layer of the atmosphere ranging in altitude from 50 to 500 km.
There are several studies that converge for the solution to this problem using another fleet or more one frequency. But the GPS fleet does not implement, the second frequency in all satellites. But after the implementation, ICAO should validate it. I will explore this subject in more detail in my next blog.
The best benefit of the air traffic management of CNS-ATM is reduced aircraft separation in IFR - Instrument Flight Rules. Aircraft can now be operated closer together, with no compromise to safety.
CPDLC is used in several countries not only from today, the conversation between ATCs and Pilots using a data link instead of voice. Its three main advantages include reduced congestion of voice channels, fewer communication errors and reduced workload for pilots and controllers.
RNP equipment must have on-board performance monitoring and alerting systems to provide assurance the system is working properly.
ADS-B uses a network of ground stations to “pay attention” to these aircraft broadcasts and transmit information to ATC twice per second and, if they have ADS-B in equipment, to the aircraft.
CNS-ATM brought an economic way of flying and safely. The routine of ATCs and pilots has changed a lot. However, during the deployments and updates of the new systems, they require a change in routine until the fine approval of the new procedures to be adopted.
Conclusion
Considering the items mentioned in the ‘Final Considerations’, I can say that the main advantage of CNS-ATM is the economy of the terrestrial infrastructure and energy. The reduction of the numbers of equipment to be installed will need fewer logistics resources for preventative and corrective maintenance.
The ground equipment needs specific requirements for its installation, a technical inspection before buying and a specific project.
After doing all of this to buy, acceptance tests on the factory, delivery, installation, acceptance tests of the installation, training in all levels, experimental operation period, the final acceptance and to receive the equipment to be fully operational.
So, CNS-ATM came to be a new idea to support flying operations with less money spent and in a safer manner.
References and Figures
https://www.allweatherinc.com/programs/flexids/
aircraft journey – phases of flight
ICAO document - 9750_2ed_en
https://www.cad.gov.hk/english/cnsatmsys.html
https://www.casa.gov.au/book-page/chapter-1-overview-cnsatm
http://estudeaviacao.blogspot.com/2012/01/cnsatm.html
DECEA CNS-ATM Aeroespaço Magazine
BLOG WRITTEN BY GILBERTO FERNANDES
Gilberto is available immediately for opportunities in Brazil and worldwide - check his profile and experience on our 'Consultants' webpage on the SpaceSpecialists website here
https://spacespecialists.com/gilberto-fernandes/
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Gilberto Fernandes is an Electronic and Telecommunications Engineer with a solid commercial background in the satellite industry, telecommunications to support aviation and an emerging technology enthusiast.
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