Give Me the Clearance, Clarence

May 10, 2005 — -- How many times have you been tempted to throw a shoe at the screen because a TV show or movie includes a terribly inaccurate cinematic portrayal of your own job or profession?

Dramatic scenes of doctors using the wrong instruments in an operation, lawyers filing a petition that would get them laughed out of court, electricians doing something that would be inevitably fatal … The list is endless. And when it comes to inaccurate portrayals of aviation, no one fares worse than the poor air traffic controller.

No wonder we all get confused when an actor playing a pilot spends an entire (fictional) transoceanic flight talking to the same tower controller he left hours ago, thousands of miles back at his departure airport, using a radio that has a maximum range of 300 miles!

Because most folks don't know how air traffic controllers fit into the equation of an average airline flight -- and because too many Hollywood inaccuracies over the years have introduced myths and more confusion -- a little clarification is in order.

Who's Who

First, there are several basic divisions of ATC involved in every flight. One is the so-called control tower staffed by men and women who handle Ground Control, Tower Control and Clearance Delivery duties for a particular airport. They work in that glass fishbowl at the top of the tower structure where they can see what's happening.

Often in the same facility (but not in the glassed-in tower cab) are the controllers who guide airplanes into and out of the airport area using radar scopes instead of binoculars. They are usually called either Approach Control or Departure Control on the radio.

For the high-altitude monitoring as you fly across the country, there are 22 Air Route Traffic Control Centers such as Denver Center, Seattle Center, Fort Worth Center, etc. An ARTCC is a large, windowless building full of electronics, computers and controllers who we've all seen depicted sitting at rows of sophisticated computer-generated radar scopes and talking quietly to the pilots flying through their "sectors," and handing off those pilots to the next sector controller at the appropriate time.

And watching over all of it from Herndon, Va., is an amazing ATC System Command Center, a windowless mission control, that has been in operation now for 10 years. Its responsibility is to take a good view of the system and keep it running as smoothly as possible.

How It Works

Now, here's how it works.

First, your pilots need an ATC clearance, which is permission to fly from one city to another along a prearranged flight path, maintaining constant communication with ATC facilities and controllers all the way. Your crew will dial up a particular frequency on their radios in the cockpit (such as 121.75 MHz, a VHF frequency) and call "Clearance delivery" to have the clearance read to them.

Second, in order to taxi the airliner from the gate to the end of the runway, the pilots will dial up another frequency and obtain a taxi clearance from the ground controller (such as Denver Ground or DFW Ground). The ground controller will tell the pilots which runway to head for, and usually what route to use in getting there, and will keep taxiing airplanes from getting in each other's way.

When the plane is at the end of the runway and ready to depart, the crew will switch frequencies again and call the tower (for example: "Denver Tower, Quantum 23, ready to go 3-1"). The tower controller, when it's clear and safe to do so, issues the takeoff clearance, which may include specific turn and climb instructions (i.e., "Quantum 23 is cleared for takeoff runway 3-1, right turn after takeoff heading 3-5-zero, climb to 6,000").

So, Quantum 23 (Quantum is my fictional airline from "Pandora's Clock"), rumbles off Runway 31, turns right 40 degrees to a heading of 350, and climbs to 6,000 feet. As the aircraft climbs away from the airport, the tower controller says, "Quantum 23, contact Departure. Good day."

When the pilots have climbed to the vertical or horizontal edge of Departure Control's airspace, the departure controller will "hand off" the flight to the air route traffic controller watching over the sector that Quantum 23 is entering, and the call will be similar: "Quantum 23, Denver Center, good morning, climb to and maintain flight level 3-5-zero [35,000 feet]."

Nearing the Destination

When the flight is within a few hundred miles of the destination airport, the process reverses and the center controller hands the flight off to an approach controller, who gives vector orders and otherwise helps the crew guide themselves to the airport, at which time the pilots are once more told to change frequencies and contact the tower for landing clearance, and then, once on the ground, Ground Control for taxi clearance.

Controllers are by and large unsung heroes in our heavily used air traffic system, but the most amazing aspect is the teamwork and partnership between pilot and controller. These are all fallible human beings, but through checking and re-checking each other and working together in a collegial fashion of mutual respect, the team routinely catches each other's human errors long before they can become safety threats.

John J. Nance, ABC News' aviation analyst, is a veteran 13,000-flight-hour airline captain, a former U.S. Air Force pilot and a lieutenant colonel in the Air Force Reserves. He is also a New York Times best-selling author of 17 books, a licensed attorney, a professional speaker, and a founding board member of the National Patient Safety Foundation. A native Texan, he now lives in Tacoma, Wash.