Within the FIR / UIRs, different types of airspace are classified internationally by ICAO so that it is perfectly clear to pilots from anywhere in the world which rules apply and which air traffic services they can expect inside a particular area.
There are two categories of airspace: con-trolled airspace and uncontrolled airspace. Within these two categories, various ‘Classes’ have been allocated in different parts, in line with a classifica-tion system for civil airspace recently introduced by the International Civil Aviation Organization (ICAO). This new system is designed to both simplify airspace structure and establish more commonality between countries.
The ICAO system grades airspace from A to G in order of importance. It begins with Class A, the highest status, which is allocated to the busiest controlled airspace.
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Controlled airspace
When, in further development, it is de-cided that an aerodrome should handle IFR traffic, it becomes necessary to protect such traffic by extending control to IFR flights and by placing additional restrictions on VFR flights. To accomplish this, controlled airspace should be established to protect the arrival, departure, and holding paths of the IFR flights.
In controlled airspace Air Traffic Con-trol is provided to all flights. It is made up of various aerodrome Control Zones (CTR), Terminal Control Areas (TMA), Control Areas (CTA) and Airways.
A Control Zone (CTR ) – is airspace around certain aerodromes in which Air Traf-fic Control (ATC) is provided to all flights.
A Control Zone extends from ground level to a specified altitude or a specified flight level (FL), de-pending on the height.
A Terminal Control Area (TMA) – is a Control Area established at the confluence of controlled airspace routes in the vicinity of one or more major aerodromes. Terminal Control Area is sometimes abbreviated as TCA, but more com-monly as TMA (from the earlier designation Ter-minal Manoeuvring Area).
A Control Area (CTA) – is a portion of airspace in which Air Traffic Control is pro-vided, and which extends upwards from a specified base altitude or flight level to an upper limit expressed as a flight level.
An Airway is a Control Area in the form of a corridor and is marked by radio na-vigation aids. Each airway has an identification code (e.g. A25 or Alpha Two Five, R8 or Romeo Eight), and extends 5 nm each side of a straight line joining certain places, with speci-fied vertical limits. All airways are Class A ex-cept where they pass through a TMA, CTA or CTR of lower status. They are used by airliners (and other Instrument Flight Rules traffic) tra-velling between the principal aerodromes. As it approaches an aerodrome, the lower level of an Airway is usually stepped down to provide controlled airspace protection for air traffic on climb and descent.
Some major trunk routes extend for thousands of miles, others are short regional links. Until 1987 they were named after
colours followed by a number between one and 999 - Amber, Red, Blue and Green, plus White for Advisory Routes - but the system became in-adequate to cater for specialized applications such as Area Navigation and Supersonic Routes. The initial letters of the five colours already in use were adopted phonetically as the basis of the new system, Amber One becoming Alpha One, Blue One - Bravo One and so on. The allocations are as follows:
a) A, B, G, R - for routes which form part of regional networks of ATC routes:
b) L, M, N, P - for area navigation routes which form part of the regional networks of ATS routes:
c) H, J, V, W - for routes which do not form part of the regional networks of ATS routes and are not area navigation routes;
d) Q, T, Y, Z - for area navigation routes which do not form part of the regional networks of ATS routes.
Where applicable, one supplementary letter is added as a prefix to the basic designator in ac-cordance with the following:
a) K (spoken as ‘Kopter’) to indicate a low level route established for use primarily by heli-copters;
b) U (spoken as ‘Upper’) to indicate that the route or its portion is in the upper space;
c) S (spoken as ‘Supersonic’) to indicate a route established exclusively for use by supersonic aircraft during acceleration/deceleration, and while in supersonic flight.
Where Advisory Service only is provided a supplementary letter D is added to the end of the designator. A supplementary letter F indicates that flight information service only is provided on the route. It should be noted that some trunk routes have common segments with dual or even triple designators. An example is G472/G463 over western Thailand. The ‘Victor’ or VOR air-way designator is peculiar to the USA and a few other countries including Japan, Turkey, and Sau-di Arabia.
Each class of airspace available to VFR op-erations has specific Visual Meteorological Condi-tions (VMC) criteria, which are expressed in terms of minimum flight visibility and distance from cloud.
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Uncontrolled airspace
Normally, uncontrolled airspace consists of Advisory Routes and Open-FIR. Open-FIR includes various areas and zones.
Advisory routes
Advisory Routes are allocated Class F. VFR operations on an Advisory Route require a flight plan to be compiled. En route, these flights then receive an Air Traffic Advisory Service from the Air Traffic Service Unit (ATSU), responsible for the route.
Advisory routes may be established in-stead of an airway in some less developed parts of the world where traffic is relatively light. It is still a narrow corridor but positive control is not imposed.
Controllers just pass information to help pilots maintain their own separation. Airways and Advisory Routes, as well as Arrival and Departure routes, are known as Air Traffic Services (ATS) Routes and each is identified by a unique designator allocated by ICAO.
Open - FIR
Open-FIR is a Class G airspace. Air Traffic services provided to flights in Open- FIR include:
„information and warnings on meteoro-logical conditions;
„changes of serviceability in navigation-al and approach aids;
„condition of aerodrome facilities; „aircraft proximity warnings;
„other information pertinent to the safety of air navigation.
Special use airspace
Aeronautical charts also depict Airspace Restrictions and Hazards. This include Danger Areas such as military weapons ranges, Prohibited Areas around critical installations, Restricted Areas for various defence purposes, Military Training Areas, and Air Defence Identification Zones.
- A Danger Area is defined airspace in which activities dangerous to flight may occur;
- A Restricted Area is defined airspace in which flight is restricted according to certain conditions;
- A Prohibited Area is defined airspace in which flight is prohibited.
Ex. 154. Comprehension check:
1. Why was controlled airspace established?
2. ATC isn’t provided to all flights in controlled airspace, is it? 3. What is controlled airspace made up of?
4. What is an airway? Give its dimensions. 5. How are VMC criteria expressed?
6. What is the special VFR clearance? How does it facilitate flights? 7. What is the procedure for penetrating an airway?
8. What does uncontrolled airspace consist of? 9. Where may advisory routes be established?
10. How do ATC controllers help pilots flying via advisory routes? 11. How are airways designated now?
12. Which supplementary letter is added to the end of an advisory route designator? 13. What does Open-FIR include?
14. Name Air Traffic Services in Open-FIR.
15. Name standard dimensions of an Aerodrome Traffic Zone. 16. How is Special Use Airspace subdivided?
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Vocabulary Practice