Fliegen über dem Atlantik

Crossing the Pond – Flying Over the Atlantic

Tim Takeoff
08.01.2019
5 minutes

Flying over the Atlantic could be so simple. Lots of water, just keep going straight ahead! Unfortunately, as always in surroundings which are inhospitable to humans, this comes with complex hurdles. Let’s start by using our imaginations.

Crossing the Atlantic was always a deep-seeded desire for early explorers and mariners. The stars were used for navigation, islands and continents were discovered. Today making a booking at the travel agent’s or online is enough to fly from Europe to North America, even on the same day. During the Concorde era the record for a crossing was under 3 hours.

No radar stations in the water

Nowadays aircraft are piloted using all kinds of navigation aids. Over land, permanently installed radar stations ensure that the air traffic controller has their eye on the situation at all times. As every aircraft is fitted with a transponder which relays its position and sends an identifier, it can always be clearly identified.

Over the Atlantic, we come up against the limitations of technology. Having no island groups or other structures, comprehensive radar monitoring cannot be guaranteed. The radar stations only have a range of a few hundred kilometres. How is it then possible to create a calculable flow of traffic over water?

NAT HLA

There is an organisation called ICAO which governs the international guiding principles of aviation. A system called “North Atlantic High Level Airspace”, NAT HLA for short, was introduced over the Atlantic many years ago. This system was designed to control the high volume of traffic between Europe and North America.

North Atlantic Tracks

This system consists of multiple sectors which are represented by the bordering countries. Whilst the east is primarily controlled by Shanwick in Ireland and the west from Gander in Canada or New York, Greenland and Iceland also feature. A special airway “track” system has been introduced for typical commercial aircraft cruising altitudes, from flight level 285 up to and including flight level 420 (a height of 8,700 to 12,800 meters). It resembles a parallel motorway system.

Time difference

Between five and eight “tracks”, or routes, between Europe and North America, all of which are clearly defined by a letter, are scheduled twice. Twice because the volume of traffic from east to west is tremendously high in the mornings at the moment. Due to the time difference, the aircraft return in the second half of the day. This means that you can fly out of Europe in the early hours of the morning and arrive in the States at dawn.

These tracks are approximately parallel with a gap of one degree. This corresponds to 60 nautical miles, or rather 111 kilometres. They all start with an entry point and end with an exit point just in front of the respective coast. The aircraft heights are staggered (gaps of 300 to 600 metres) between 1,000 and 2,000 feet.

How does this work exactly? The tunnel example

Every track can be imagined as a kind of tunnel. These tunnels are clearly defined using waypoints and the above-mentioned distances. If an aircraft wants to use one of these tunnels, this is recorded in the relevant flight plan which is available to the air traffic controller. When the jet is approaching the entry point, the “tunnel entrance”, it reports to the relevant air traffic control for the sector. They then award a so-called “oceanic clearance”, special clearance for crossing the ocean. The aircraft is then assigned one of the clearly defined tunnels (tracks). Furthermore, the pilots receive a fixed cruising altitude and are allocated a constant speed to which they must stick. The airborne computer is fed this information.

Separation

The aircraft enters the tunnel system with fixed values which are easily calculable for the air traffic controllers. The next aircraft will enter the same tunnel with the same values. Precise intervals, known as separation, are guaranteed because the intervals are absolutely exact due to the equal speeds. Whereas separation with radar control requires a minimum interval of five minutes between the jets, without radar, namely over the Atlantic, it is a cool 15 minutes. All aircraft fly above a certain height and with the same atmospheric pressure setting so that separation can also be easily achieved vertically.

You can see the reality of how separation like this can look in this video:

Wind

And what about the wind? Because the aircraft all move within one and the same air mass, and are therefore exposed to the same wind, superficially this plays an insignificant role. The pilots are required to report on their position at specific waypoints. Using these reports, the air traffic controller can estimate whether the distances between the aircraft have changed. If anything serious happens here, the pilots receive new instructions. A different speed or cruising altitude, for example.

However, the wind does play a very different role, namely in track selection. The flight from east to west usually lasts significantly longer than the return journey because there is often a strong jetstream from west to east. As all airlines have the same problem, the air traffic control units try to position the tracks as tactically as possible. The morning east to west wave of aircraft can circumnavigate the jetstream whereas the flow from west to east can mostly fly directly into the jetstream in order to harness as high a tailwind element as possible.

Random tracks

If none of the official tracks suit an airline, there is also the possibility of “random tracks”. Here the operator can post a specially tailored flight plan either without or with only partial track system use. The flight plan is checked by the air traffic controllers, adapted as required and released.

Radiotelephony and text messaging

For years people were dependent on using shortwave radio to ensure communication over water. This radio has very poor quality but works over large distances. Nowadays there is also the option for pilots and air traffic controllers to use a kind of text messaging system. This means that predefined or freely composed messages can be exchanged digitally. Essentially it works so that initial voice contact can be made on the shortwave radio. The text message system can then be tested using a kind of “bell”. If this works without fault, the pilots can switch off the shortwave radio’s noisy, crackling and unintelligible background noises. All position reports can then take place using the text messaging data system. If the air traffic controller wants to initiate voice contact with the pilots, calling using this “bell”, a so-called “selective call” or “SELCAL”, is sufficient. The pilots immediately tune in to the previously appointed shortwave radio frequency again and can establish contact with the air traffic controller.

Emergencies

There are also special procedures for emergencies so that aircraft in the different tracks do not get in each other’s way. For example, an aircraft with technical problems can be diverted to the “middle”, between the tracks, and a descent can take place to beneath the NAT HLA system height. Below this height, the course can be changed towards an alternative airport in consultation with the air traffic controller.

The future lies in outer space

In the future it will be possible to completely dispense with this old technology due to increasingly modern systems. Even now, the air traffic controller can view a display which is similar to radar using satellite contact. Aircraft can already be clearly identified without radar using systems such as ADS-B and ADS-C. As soon as this has been shown to be reliable in the long term, air transportation will have taken another step towards increased safety.

Click here to find out more about modern flight navigation. Do you want to follow all of the aircraft “crossing the pond” yourself? Then take a look at the “flight radar”.

In this (English language) video you can discover more about route planning for flying across the Atlantic:

by Tim Takeoff

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