There are huge gaps in the radar coverage. The trans-oceanic flights will follow set routes (tracks) at set altitudes.

The NATs (North Atlantic Tracks) are from North America to western Europe, ranging from 29-41,000 feet in altitude. The actual tracks vary from day-to-day to compensate for wind and weather.

Oceanic Center Controllers will approve/assign the track to the flight and calculate separations and estimated ToA (time of arrival).

The crew report back to the controllers as they cross waypoints in the track. If the flight cannot meet the waypoints (speed, weather, etc.) the controller will adjust other flights or call in a contingency plan.

Air Traffic Control is handled by spacing departures at least 80 miles or 20 minutes apart. Pilots give position reports at predefined check-in areas and controllers are blind when pilots are not in radar coverage. Pilots are not without radio contact, but often without radar coverage, which extends no more than a couple of hundred miles out to sea. Pilots fly specific routes determined by ATC called NATs or flight tracks that are based on weather aloft and winds.

Radar is a WWII era technology and is actually becoming unnecessary in part to a new system called ADS-B. This technology of the future is known as Automatic Dependent Surveillance Broadcast. It takes highly accurate position reports broadcast automatically by airplanes and it creates a radar-like display for air traffic controllers. It is far more accurate and faster than radar and it will allow planes to fly more closely together. It will also help keep tabs on airplanes across oceans, where airplanes must fly at least 80 miles behind each other for spacing. Canada and Greenland have launched this system.