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  • Raghav Sand

How Air Traffic Works

Air traffic control aims to move aircraft safely and efficiently through the airspace system. Controllers keep aircraft set distances apart while moving them from airport to airport using set routes. It is a complex and labour-intensive operation. Wind direction and velocity of the aircraft determine flight operations. Aircrafts land into the wind and during take off after the initial heading, they fan out to the designated route. There are separate routes for departures and arrivals.

Mid-air, aircrafts must keep a lateral gap of five kilometres and eight kilometres in low and high altitude, respectively. Vertically they must be at least thousand feet apart below 41000 feet. Global positioning system has made flights shorter, cheaper and precise. Time-based metering – delivering aircraft to a specific place at a specific time – allows air traffic controllers and managers to manage aircraft in congested airspace more efficiently by smoothing out irregularities and delivering a more consistent flow of traffic down to the runway. It also enables an aircraft to join other aircrafts on the similar route without disrupting air traffic.

An illustration of Time-based metering Image Courtesy: Federal Aviation Administration

From the time you as a passenger board the plane, your flight is already being handled by air traffic controllers in the airline’s dispatch office. What most people don’t realize is that while your flight is still at the departure gate, there’s all sorts of planning going on that dictates when the plane pushes back and begins its taxi route out to the runway. Of course, changes in weather even hundreds of kilometres away, can affect your flights.

Before Take off

Airlines file a flight plan with air traffic control. Every controller who deals with the flight on its journey is aware of its details and route. When an aircraft is at an airport, the pilots on board will be in contact with controllers in the airports control tower. Air traffic controllers will look after the aircraft while it is on the ground and give it permission to take off.

In the Air

Once airborne, the pilot will then normally talk to another controller using a radar screen to track the aircraft’s progress through the airways system (equivalent to highways in the sky). Each air traffic controller is responsible for the aircraft in a set piece of airspace. When an aircraft is nearing the edge of their sector they will coordinate its handover to the next controller. This will continue through the aircraft’s journey until it is handed over to the controller at the destination airport.

Most airliners are monitored by controllers using radar in airways and routes known as ‘controlled airspace’. The majority of airspace that is left is known as ‘uncontrolled’ and this is used by the military and recreational pilots. In this airspace some air traffic control services are provided, especially near airfields, but in much of the airspace it is the pilots’ responsibility to see and avoid each other. Some areas may have a temporary flight restriction. Such constraints are placed where heads of state are on tour or important public events are taking place.

What’s a TRACON?

It stands for Terminal Radar Approach Control Facility. That’s the air traffic facility where controllers handle the communications and surveillance of traffic departing from or arriving to an airport. It’s one leg of the three-legged stool for air traffic — towers, TRACONs and air route traffic control centres. And, they are the facilities and controllers that handle the cruise portion of a flight.

What is VFR, and what’s IFR?

VFR or Visual Flight Rules, means pilots may or may not have to talk to air traffic control, depending on where they’re flying, of course. VFRs typically the choice for light general aviation pilots, especially those who fly in good weather conditions. Airlines on the other hand are almost always operating on IFR or Instrument Flight Rules flight plans. For IFR, the pilot or the airline files the flight plans, which are entered into the air traffic control automation systems.

An IFR flight has rigorous communications, navigations and surveillance requirements that, when combined with Air Traffic Control procedures, and professional pilots, controllers and dispatchers, make sure aircraft are safely separated and on track to reach their destinations on time, even when bad weather or other issues crop up.

There’s only about eight – ten kilometres around the tower, generally, that a pilot is actually talking to a tower controller. And then they will do a radar handoff, which is flashing from one sector to the other that has the flight number on it, to the TRACON, which may have anywhere from 30 to 60 kilometres away from the airport up to about anywhere from 15,000 to 23,000 feet.

The Descend and Landing

Traditionally, the descending aircraft followed a falling down the flight of stairs approach. It involved descend, applying speed brakes, levelling off and powering the engine. This procedure was repeated till the time an aircraft was ready to make its final approach towards runway.

Optimised Profile Descend Image Courtesy: Federal Aviation Administration

In contrast, the modern descend operations follow optimised profile descend (OPD). Here, the speed and altitude at various points of the route are fed to the flight computer. OPD enables less interaction between the pilot and the controller. The aircraft glides on idle power and reduced use of speed brake produces less noise and emissions.

Whenever you take the next flight, try to visualize and familiarize yourself with some of the behind the scenes action. Air traffic operations may seem simple and routine, but in reality its like an orchestra where various instruments and musicians are trying to produce flawless symphony.

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