Ask the Captain: How do planes communicate over ocean?

Question: When flying from the East Coast of the U.S. to Europe, how long are aircraft out of radar contact before reaching it in Europe?

— Submitted by reader T. Jones, Tennessee

Answer: Civilian radar ends about 200 miles from the coast. A New York-to-London flight is an average of seven hours, and the portion when it's over the ocean and out of radar contact is four hours. (These are very approximate figures and intended to show that more than half of the flight is out of radar.)

Q: How do aircraft crossing the ocean keep in contact with air-traffic control?

— John, Hawaii

A: Modern airplanes use satellite communication to talk with air-traffic control. There is an older technology, High Frequency Radio, that can be used, but it is not as reliable.

Q: Is radio/controller access limited during trans-Atlantic flight? What are the various options pilots have to make sure they fly a safe distance from other aircraft?

— Roshan S, South Brunswick, N.J.

A: Flights over the ocean (or remote parts of the jungle) are separated by time and altitude. When flying over specific latitude/longitude points, the pilots report their position to air-traffic control. The controllers know the estimated time of other airplanes in the area to the same point in the sky. Using these estimates, airplanes are kept miles apart and at least 1,000 feet vertically separated.

Most airliners have a Traffic Collision Avoidance System (TCAS) onboard that shows nearby traffic and will provide separation commands if there is a conflict.

Q: We were mid-ocean on a flight from Europe to NYC. I saw another big plane flying in the opposite direction — just below us. In all the vastness of the ocean, is it normal for two planes to pass each other so closely?

— Richard Guthrie, Albany, N.Y.

The routes are determined to take best advantage of the winds and minimize the distance; consequently, airplanes will often pass in close proximity. The vertical separation is always 1,000 feet or more.

John Cox is a retired airline captain with US Airways and runs his own aviation safety consulting company, Safety Operating Systems.