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Part Three
Planning and control
Case study
Air traffic control – a world-class juggling act
Air traffic controllers have one of the most stressful jobs in
the world. They are responsible for the lives of thousands
of passengers who fly every day in and out of the world’s
airports. Over the last 15 years, the number of planes in the
sky has doubled, leading to congestion at many airports
and putting air traffic controllers under increasing pressure.
The controllers battle to maintain ‘separation standards’
that set the distance between planes as they land and take
off. Sheer volume pushes the air traffic controllers’ skills to
the limit. Jim Courtney, an air traffic controller at LaGuardia
airport in New York, says: ‘There are half a dozen moments
of sheer terror in each year when you wish you did something
else for a living.’
New York – the world’s busiest airspace
The busiest airspace in the world is above New York.
Around 7,500 planes arrive and depart each day at New
York’s three airports, John F. Kennedy, LaGuardia and
Newark. The three airports form a triangle around New York
and are just 15 miles from each other. This requires careful
coordination of traffic patterns, approach and take-off routes,
using predetermined invisible corridors in the sky to keep
the planes away from each other. If the wind changes, all
three airports work together to change the flight paths.
Sophisticated technology fitted to most of the bigger
planes creates a safety zone around the aircraft so that
when two aircraft get near to each other their computers
negotiate which is going to take action to avoid the other
and then alerts the pilot who changes course. Smaller
aircraft, without radar, rely upon vision and the notion of
‘little plane, big sky’.
During its passage into or out of an airport, each plane
will pass through the hands of about eight different controllers.
The airspace is divided into sectors controlled by
different teams of air traffic controllers. Tower controllers at
each airport control planes landing and taking off together
with ground controllers who manage the movement of
the planes on the ground around the airport. The TRACON
(Terminal Radar Approach Control) controllers oversee the
surrounding airspace. Each New York air traffic controller
handles about 100 landings and take-offs an hour, about
one every 45 seconds.
TRACON controllers
The 60 TRACON controllers manage different sectors of
airspace, with planes being handed over from one controller
to the next. Each controller handles about 15 planes
at a time, yet they never see them. All they see is a blip on
a two-dimensional radar screen, which shows their aircraft
type, altitude, speed and destination. The aircraft, however,
Error-free control is particularly important where people
are being processed, as is the case for these air traffic
controllers
are in three-dimensional airspace, flying at different altitudes
and in various directions. The job of the approach controllers
is to funnel planes from different directions into an
orderly queue before handing each one over to the tower
controllers for landing.
Tower controllers
The tower controllers are responsible for coordinating
landing and taking off. Newark is New York’s busiest airport.
During the early morning rush periods, there can be
40 planes an hour coming into land, with about 60 wanting
to take off. As a result there can be queues of up to
25 planes waiting to depart.
At LaGuardia, there are two runways that cross each
other, one used for take-off and the other for landing. At
peak times, air traffic controllers have to ‘shoot the gap’ –
to get planes to take off in between the stream of landing
aircraft, sometimes less than 60 seconds apart. Allowing
planes to start their take-off as other planes are landing,
using ‘anticipated separation’, keeps traffic moving and
helps deal with increasing volumes of traffic. At peak times,
controllers have to shoot the gap 80 times an hour.
Most airports handle a mixture of large and small
planes, and tower controllers need to be able to calculate
safe take-off intervals in an instant. They have to take into
account aircraft type and capabilities in order to ensure
that appropriate separations can be kept. The faster
planes need to be given more space in front of them than
the slower planes. Wake turbulence – mini-hurricanes which
trail downstream of a plane’s wing tips – is another major
factor in determining how closely planes can follow each
other. The larger the plane and the slower the plane, the
greater the turbulence.
Source: Arup