Flying the Atlantic
Everyday hundreds of aircraft fly over the North Atlantic without colliding with each other. Not bad you say except for one thing. There is no Radar Service by Air Traffic Control to help the pilots in the Atlantic. So how is the system operated that prevents collisions ?
Firstly the Atlantic traffic flows are Eastbound overnight and Westbound during the day. Aircraft must be fitted with modern day navigation equipment. Each day tracks are drawn up avoiding bad weather and headwinds where possible. (Tracks making use of tailwinds if possible.) These winds are sometimes known as Jet Streams. They are very strong.
Each day the tracks are published and given a letter. Westbound tracks start with the letter A. A being the most Northern. Eastbound tracks start with the letter Z. Z being the most Southern Track. Tracks always start and finish in the same place. The middle part alters daily. The Start and End points are the junction of the European and North American Airways Radar Service Area. The remainder of the flight is then done under the radar service of ATC using the airway system.
Between start and finish points Waypoints are created using longitude and latitude coordinates. Each time the aircraft passes a waypoint the pilot will report this to Air Traffic Control giving callsign, the waypoint at, time at the waypoint height and estimate for the next point. The system is designed so on the same track at the same height a ten minute flight interval applies at all times. The tracks are 60 miles apart on either side of the aircraft.
Separation
Aircraft on the same track at the same height to the front and rear must be separated by 10 minutes time interval .To the left and right the track separation is 60 miles. Use track C for reference in the diagram below. this view is looking down from space. A set of tracks is linked below with waypoints on.
Above and below the aircraft Vertical Seperation of 1000 ft applies at 1000 Ft Flight levels
At any one time 200 aircraft may be flying across the Atlantic at the same time. They will all be flying at different heights and speeds . It is not uncommon to be flying at 35000 ft at Mach. 80 to see an aircraft above or below passing you traveling at Mach .84
Rules for Pilots
Aircraft are not allowed into the Oceanic Airspace without a clearance. Taking off from Ireland or Scottish Airports, the clearance will be obtained by telephone before start up, as the flying time is insufficient to the start point for ATC to approve the clearance. For UK and European airport departures the pilots will call the Oceanic Centre when airborne with a request for the track they want. &The height they want to fly at, & the speed and the time at the start point. This is worked out before they take off in the preflight briefing. They will also work out other alternative heights or track suitable in case the preferred track is not available. It is very much a first come first serve basis, as most aircraft want the same tracks at the same height and speed.
ATC will then check that the track and height is available, bearing in mind the separation standard described above. If it is not available then perhaps another height maybe available or another track with the height requested. So negotiation goes on until the Captain is happy with his clearance or a compromise is reached with Oceanic Air Traffic Control. Many of these clearances are obtained by Datalink from the Flight Deck FMC computer. Less radio requests are made on VHF talk radio now. It maybe that the aircraft may hold on route at the start point or adjust speed so as to enter the start point at the correct time. Depending where the flight is going the pilots decide which track is best for them.
The North Atlantic is Controlled from Prestwick in Scotland callsign SHANWICK or Gander in Canada. Iceland borders the area to the North at Reykjavik . To the South Santa Maria and New York Control the Atlantic.
Many Twin Engine aircraft cross the Atlantic they are governed by ETOPS procedure. a seperate article has been made on this so you understand the considerations the pilots have to make.
Below are some illustrations of what I discussed above so you can understand what it is about. One of the most important checks the pilot makes is to ensure the aircraft clock is set correctly to UTC time. As all reports are done using ATC time. (UTC is also known as GMT).
VHF Radio is no use in the Atlantic as it is out of range. Communication is by High Frequency Radio. The system is called SELCAL. It works a bit like a mobile phone. Each aircraft has its own id number. If ATC want to talk to them they will selcal the aircraft by dialling the Selcal number. many positions reports or conversation are now done by Datalink.
I hope this gives you a basic idea on how the Atlantic system works. Please now read the ETOPS operation. Non ETOPS aircraft cannot use all the tracks in the Atlantic and will route via ICELAND.
Each time the pilot gets to a waypoint he notifies ATC and gives an estimate for the next one. This in then monitored by ATC to ensure the seperation time is ok.
Point of Interest
(Pilots in Africa and other parts of the world monitor a frequency and give each other positions reports as in some areas no ATC radar coverage is available. TCAS is on most flight decks so pilots can monitor other aircraft in the area.) Pilots make position reports 5 minutes normally before each beacon or fix.
I have put up some maps on my Virtual Airline giving a set of tracks in both directions. These are based on the real world track system on a given day. To complete this lesson you may like to look at them and perhaps use them for your flightsimming. The maps will take a time to load. You may also want to look at ETOPS which relates to Twin Engine Operations over the Atlantic