Each day, over 2000 aircraft travel across the Atlantic Ocean bound for North America or Europe on the North Atlantic Organized Track System. Have you ever wondered how pilots navigate and communicate during the journey? Communication over the Atlantic is an interesting combination of modern digital messaging, satellite communication, and early 1900′s low-tech!
A note from the AeroSavvy Barrister (Not to be confused with the AeroSavvy Barista).
This article has been written to give the reader a general idea of the procedures used on a trans-Atlantic flight. Actual procedures, messages, and radio contacts will vary based on aircraft equipment, airline, and the route flown. For heaven’s sake, don’t try flying an airplane over the Atlantic using this as your guide!
AeroSavvy 105 flight crew: Preflight Briefing
To see how it all works, we’ll ride along with AeroSavvy Airlines flight 105 from New York JFK to London Heathrow.
AeroSavvy 105 will depart JFK around 7:00PM EST. The flight is one of several hundred aircraft, all heading the same direction across the Atlantic.
North Atlantic Track system (NATs) – Routes across the pond
Before we can fly across the Atlantic, we need to select a track (or route).
Every day, from 0100z – 0800z (8 pm – 3 am EST) hundreds of airliners fly eastbound from North America to Europe. From 1130z – 1900z all that traffic flies back to North America. Why those times? Because that’s when most passengers want to fly these routes.
Several hundred aircraft converge on the North Atlantic tracks twice a day. Photo: Gopal Vijayaraghavan
To accommodate the twice-daily stampede, air traffic planners in Gander, Newfoundland and Prestwick, Scotland create weather optimized routes across the Atlantic, called the North Atlantic Organized Track system (NATs). NATs are like a multi-lane, one-way highway in the sky. The tracks change each day to provide the most efficient routes for the airlines. A track NOTAM (Notice to Airmen), also called a “track message,” that defines each day’s tracks is published online.
Airline dispatchers and pilots use the published tracks to plan the day’s flights. Each track is labeled by a letter to make it easy to reference on a flight plan. Westbound tracks are labeled A, B, C, D, etc. Eastbound track labels are at the end of the alphabet (W, X, Y, Z). Click on the track message image to see how it looks. The chart below can be used to help decode the information.
North Atlantic organized tracks were first used in 1898 for commercial shipping! Daily publication of tracks for aircraft use began in 1965.
Each airline requests a track that will give their flight the best fuel efficiency. For our flight to London, AeroSavvy 105′s dispatcher requests track “Uniform” in our flight plan.
Using the track message above, I highlighted and labeled the day’s tracks on a North Atlantic plotting chart. The next image shows our requested track Uniform by itself to better display the geography.
The air traffic controllers in Gander, Newfoundland will assign us our actual track as we approach their airspace. Sometimes, due to traffic congestion, we’ll be assigned a different track than we requested. If that happens, we’ll reprogram our navigation system with the new route and be on our way.
Eastbound Track Uniform for 09-Feb-2016
Time to Get a (Partial) Route Clearance
About 30 minutes before a flight departs, the crew contacts air traffic control to receive a route clearance. For most domestic and trans-Pacific flights, ATC issues the crew a complete route from start to finish. For Atlantic crossings, the route clearance covers the beginning and ending domestic portions of the flight. We won’t find out which track we are assigned until we are airborne and approaching the track system. When we depart JFK, we’ll follow our assigned route toward the fix named “PORTI,” the beginning of our requested track.
The Flight Management Computer’s Control Display Unit (CDU) manages our digital communications.
On our way!
AeroSavvy 105 is off the ground and heading northeast toward Nova Scotia. About an hour after departure it’s time to start thinking about our oceanic clearance. A few years ago, all the clearances were issued by voice over the radio. Digital communications have made it much easier. We’ll get our oceanic clearance and track assignment by ACARS, a type of data and text messaging system. With a few button presses, we send the request about 90 minutes before reaching our oceanic entry point.
It can take anywhere from a few minutes to an hour to receive an oceanic clearance from Gander. The controllers must take all the requests and make sure aircraft are appropriately spaced along the tracks. After a short wait, our cockpit chime rings and our oceanic clearance is ready to view. Today, we have been cleared across the Atlantic on Track Uniform as we requested.
AeroSavvy Flight 105′s Oceanic Clearance
Printing out the clearance.
A little in-flight record keeping:
Whenever we receive a clearance via ACARS or CPDLC, we print it out. It’s nice to have a hard copy to reference. The printer uses a thermal print head and rolls of heat sensitive paper. It’s easy to use and looks like a paper tower dispenser!
No Radar? How Will Air Traffic Control “See” Us?
There’s no radar over the ocean, but oceanic controllers must still make sure all the aircraft are safely separated by distance and altitude. Since they can’t “see” the aircraft, controllers rely on pilots to report their position at regular intervals. A position report provides an aircraft’s location, speed, and altitude so the controller can build a 3D picture of all the traffic. In the old days, pilots reported their position by HF radio every 10° longitude. Now it’s digital (and much easier).
As we get closer to PORTI, our oceanic entry point, the flight 105 crew will do an ADS/CPDLC logon to Gander Center. ADS (Automatic Dependent Surveillance) is the system that makes our position reports for us. It allows controllers to request and receive digital reports from the aircraft’s navigation system without bothering the crew.
CPDLC stands for Controller Pilot Data Link Communications. It allows pilots and controllers to send requests and clearances back and forth via text. Aviation text messaging without the LOLz & . ADS and CPDLC can send data over SatCom (satellite), VHF, and HF radio so they work great over the ocean.
As we approach PORTI, our track entry point, we need to logon to Gander’s CPDLC and ADS systems.
Logging on to CPDLC and ADS is a super easy. We fill in three blanks and click SEND:
- Facility: CZQX (Gander Center)
- Flight number: ASV105 (AeroSavvy 105)
- Aircraft tail number: N10ASV (the pride of the fleet!)
A few seconds later, an “ATC COMM ESTABLISHED” message appears. This means that our computer is talking to the air traffic control computer. It’s easier than posting a Facebook status!
Connecting to CPDLC and ADS is easy. Both systems use the same logon.
HF Communications Check
Fancy digital communication is awesome, but we still need a backup in case the technology fails (that could never happen, right?).
Aircraft VHF radios have a very short range, so they are of little use over the ocean. For backup communications, we use old-school HF (high frequency) radios. HF has been used in aviation since the 1920s. It’s reliable and the signals can easily reach across the ocean. The downside is that transmissions are sometimes difficult to hear. It’s like listening to a distant AM radio station at night; lots of static.
As we approach our track entry point, Gander Center will give us the HF frequencies for Gander Radio and the next frequencies we’ll need halfway across the Atlantic. The controller then bids us farewell: “radar services terminated, have a nice day!”
Time to contact Gander Radio on HF…
Gander Center (VHF) vs. Gander Radio (HF)
Facilities with a call sign suffix of “Center” (Gander Center), usually transmit on VHF radios. The pilots talk directly to the air traffic controllers.
Facilities with a call sign suffix of “Radio” (like Gander Radio) are typically HF radio services staffed by professional operators. The operators relay information between air traffic controllers and pilots.
After saying hello to Gander Radio, we’ll need to monitor their HF frequency in case the operator needs to talk to us. Listening to HF static for hours is miserable. Fortunately, we can use a system that was introduced in 1956 called SelCal (Selective-Calling) to monitor the radio for us. Each aircraft with HF has its own SelCal code assigned to it. The codes are two pairs of letters (like CG-MS). Each letter corresponds to an audio tone frequency. When radio operators need to contact an aircraft, they transmit the aircraft’s SelCal tones (they sound like telephone touch-tones). The tones trigger a chime in the cockpit to alert the crew they are needed on the frequency.
Here’s an audio clip of AeroSavvy 105 making its initial contact with Gander Radio. The operator will give us a quick SelCal check to make sure our chime rings in the cockpit:
Here’s the transcript of the audio clip: [Text in brackets added for clarification]
[Tone generated as HF radio tunes the selected frequency]
Gander Radio, Gander Radio, AeroSavvy 105 on five-six [five-six is the first two digits of the frequency we are using (they monitor several frequencies)]
AeroSavvy 105, Gander, good morning, go ahead.
Gander Radio, AeroSavvy 105, SelCal Charlie Golf – Mike Sierra, Shanwick next, over. [Our SelCal code is CG-MS and we are heading towards Shanwick Oceanic Control]
AeroSavvy 105, here’s your SelCal. <SelCal tones> <Cockpit chime> [Our system recognizes the SelCal tones and rings the chime in the cockpit.]
Gander, AeroSavvy 105, SelCal OK, over. [Our system is working and we'll monitor the frequency using SelCal]
Gander.[Short reply meaning: "Nice talking to you, fly safe, say hello to the family!"]
It’s been a busy few hours, but AeroSavvy 105 is now headed out to sea. Gander Center will use ADS to periodically check our position to assure adequate spacing with other traffic on the track. On a typical flight, we won’t need to talk to anyone again until we approach 30 west longitude. At 30 West, we’ll switch over to Shanwick Oceanic Control, which raises the question: Where the heck is Shanwick? Don’t bother checking a map of Ireland or Scotland; you won’t find it.
Shanwick Oceanic Control at 30 West
The east Atlantic region that AeroSavvy 105 will overfly is called the Shanwick Oceanic Control Area. Administration of the area is a joint venture that began in 1966: HF communications are based in Shannon, Ireland, and the air traffic controllers are located in Prestwick, Scotland. The city names were combined to create Shanwick.
Approaching 30 west longitude. The border between Gander and Shanwick Oceanic Control
Just before reaching 30 West, the AeroSavvy 105 flight crew finishes breakfast, turns up the HF radio volume, and contacts Shanwick Radio on the HF frequency provided by Gander a few hours earlier. The radio call is similar to the previous one, except the operator won’t have a Canadian accent. After another SelCal check, the crew will have an hour of peace and quiet before things get busy approaching London. Our CPDLC and ADS will automatically log off Gander’s system and logon to Shanwick like magic!
Beer drinking aviation fans sometimes refer to 30 west longitude as the “Molson/Guinness Line.”
If you’re crossing the Atlantic (as a passenger), celebrate the halfway point with a mug of suds. Cheers!
Exiting Oceanic Airspace
The final (and easiest) part of flying a North Atlantic Track is leaving it!
As our flight approaches LIMRI, we’ll contact Shannon Control on VHF.
A few minutes before reaching LIMRI and XETBO, our oceanic exit points, AeroSavvy 105 will receive a CPDLC message like the one below. At 0520z (about the time we are over LIMRI) the crew contacts Shannon Control on VHF to receive a warm welcome, a new transponder code, and any updates to the route into London. This completes the oceanic portion of AeroSavvy 105. We made across the pond!
Time to contact Shannon Control as we enter domestic airspace!
North Atlantic Tracks Q&A
A westbound random route clearance issued while eastbound tracks are active.
Q. What if a flight needs to go the opposite direction of the track system?A. If a flight can’t utilize the tracks, it can fly a “Random Route.” Random routes are carefully planned by dispatchers or pilots and must be approved by air traffic control. The routes are required to stay away from the NATs (or fly under them) to avoid interfering with traffic. Random route clearances are issued the same way as track clearances.
Cargo flights often fly across the Atlantic at times when the tracks are flowing in the opposite direction, so they fly random routes.
Q. Just how busy are the NATs?
A. Check out this amazing visualization produced by NATS (National Air Traffic Services), the main air traffic control provider in the UK. It covers a 24 hour period over the North Atlantic. Watch carefully to see “random route” flights flying opposite to the direction of the tracks (full screen and audio highly recommended!):
AeroSavvy knows a lot about flying, but not everything! I’d like to thank three fellow professional aviators (and Twitter celebs) for helping me improve this article. If you’re on Twitter, be sure to follow them!
Ken Hoke has been flying for over 30 years. He’s currently a Boeing 757 & 767 captain flying international routes for a package express airline. In his spare time, he writes AeroSavvy. Follow Ken on Twitter, Facebook,Instagram or YouTube.
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