How we fly by the minute: Highways at 30,000ft

It is a widely known fact that air travel is currently the safest mode of travel. This is due to the fundamental principles used in all modes of transportation: "Corridors". For instance, if you want to visit the shop down the road in your car, there are roads that will lead you there. Same for the railway industry. If you'd like to get to a certain destination, the appropriate train will take a specific route through the tracks. Similarly, for an airplane to get from its point of origin to its destination, there are 'corridors' or highways in the sky that it must follow. This ensures safety, efficiency and a strict structure each flight must follow, just like you in your car or the train or even a ship. Out on the road, they're called 'roadways', for trains they're called 'railways' & in Aviation they're called ... you guessed it .. 'Airways'. It is due to these carefully planned and organized airways in the sky that allow you to travel from your departure airport to your destination airport with the highest safety standard.

What is an airway?
According to the ICAO Annex 11 [1], an airway is a control area or portion thereof established in the form of a corridor. They are also referred to as "ATS Routes" in AIP (Aeronautical Information Publications).

To explain in simple words, Airway is an air route which starts from waypoint A and ends at waypoint B
For Eg: The Q1 Airway in India starts from the Mumbai VOR (BBB) and terminates at Delhi VOR (DPN).

Similar to how the Railway route from Mumbai to Delhi has several stations in between, an airway has several navaids or waypoints in a specific order which defines that route.
For Eg: Taking the previous example, the waypoints which define the Q1 Airway are :
  • BBB (Mumbai VOR) - Start
  • DPN (Delhi VOR) - End
Did you know, Mumbai - Delhi is the 3rd busiest air route in the world with 130+ daily flights!

As discussed before, an airway is defined by several waypoints in a specific order. These waypoints are nothing but a geographical location defined by latitudes and longitudes. A Waypoint can also be a geographical location of a navigational aid such as VOR or NDBs
Eg: For the Airway W141 is defined by
  • Waypoint BIA which has a geographical location of  131225N 0774356E 
  • Waypoint VEMBO which has a geographical location of  133530N 0785000E 
  • Waypoint TTP which has a geographical location of  133806N 0793349E 

Most of the modern airliners have a FMS/FMGS (Flight Management System/Guidance System) which store a database of these waypoints and airways. So , if the pilot enters W141 in the route section of the FMS , it will plot a route from location 131225N 0774356E to 1133530N 0785000E to 133806N 0793349E .

Now since the computers know the exact precise location of the planned route, pilots can fly the airplane to that exact location with help of autopilot. The computers are so advanced that they even give you the exact altitude and even the exact time at which you will cross the waypoint if you are climbing or descending.
Airways/ATS Routes has made flying from one airport to another airport very easy. Since there is a database of predefined airways and the waypoints, it makes it very easy to navigate from one airport to another. 

Advantages for the Air Traffic Controllers (ATC): 
In a busy airspace , most of the airplanes are modern jetliners which have a FMS and are capable of flying the ATS Routes very accurately. This helps the ATC to manage traffic as they are aware of the current position as well as the next intended location of the aircraft. So with the help of secondary radar systems , there is no ambiguity or confusion about the aircraft's location. Technology is so advance today that due to such sophistication , we can predict if there will a mid - air collision hours before it can actually occur.

Types of Airways/ATS Routes as per ICAO: 

1. RNAV5 : 
  • ± 5 NM for 95% of the flight time*
  • Route spacing – Low ATC intervention rate
    - 16.5 NM uni-directional
    - 18 NM bi-directional
  • Route spacing – High ATC intervention rate
    - 10 -15 NM
2. RNAV2 :
  •  ± 2 NM for 95% of total flight time*
  • Route spacing at least 8 NM
3. RNAV1
  •  ± 1 NM for 95% of total flight time*
* Tolerance in deviation from the airway. If its ± 5 NM that means that the airway has a width of 5nm which allows 2.5nm deviation from either side of the track.

New Day , New Tracks : 
There are few airway tracks in the world which change everyday. They are mostly situated over Oceans where is is limited radar coverage. They are designed in such a way that the aircraft have minimum headwinds and maximum tailwinds which increases the efficiency and reduces the flight time. Since the enroute weather cannot be same everyday , these kind of airway tracks are planned and published everyday. 2 of such Airway tracks are

  • NATS - OTS : North Atlantic Organised Track System.
    They connect the North America and the European Continent

  • PACOTS : Pacific Organised Track System
    They connect the Asia and the West Coast of North America

  • AUSOTS :  Australian Organised Track Structure
    They connect Australia with the Indian Ocean

References :
1. ICAO Annex 11 - Air Traffic Services
3. ICAO PBN Workshop

Picture Credits :
1. Wikimedia Commons
3. Flight Service Bureau®

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