November 1956 Popular Electronics
Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
published October 1954 - April 1985. All copyrights are hereby acknowledged.
The VOLSCAN (Volume
Scanning) radar system was a paradigm changer for air traffic controllers charges
with guiding aircraft while assuring safe separation. Busy terminal areas were a
particularly difficult challenge due to the large variation in aircraft speeds and
types. VOLSCAN was a computer that tracked the position, direction, and speed of
each target and even made recommendations to controllers for course assignments.
It also warned of impending dangerous scenarios. Another VOLSCAN article in the
July 1954 issue of
Radio-Electronics magazine went into more detail and had
color photos of the equipment. Interestingly, the equivalent of maybe the world's
first light pen computer interface is used by the operator for letting the processor
know what part of the screen (PPI, or plan position indicator) he is referring to.
Here is an IEEE Xplore article on
Radar Tames the Wild Blue Yonder
By Shane Smith
The sky, once empty and beyond reach, is now a busy thoroughfare. Aviation has
shrunk space aloft as well as on the ground. With the planes themselves made safe
by today's superb engineering, congestion of the air has become the chief risk of
As the wild, blue yonder grows wilder and more dangerous with fast planes crowding
each other for space, the future of flying now depends on electronic aids to air
Volscan, developed jointly by the Cambridge Research Center of the Air Force
and the Crosley Corporation, is the latest answer to the urgent problem of air traffic
control in the vicinity of busy airports. Combining ordinary radar data, Volscan
converts a cloud of randomly arriving aircraft into an orderly, safe procession.
Giant overhead radar scope displays total air traffic situation.
As newly arriving plane enters the monitored air space, an electronic computer coordinates
its position and progress with every other plane in the area.
Operators relay instructions to incoming aircraft in terms of
azimuth and elevation.
A supersonic jet plane may require as much as 50 miles for its landing approach,
with some elbow room at either side. Therefore, an air traffic control system must
assign each incoming aircraft a long "block of space" reserved exclusively for its
use. Volscan automatically marks this space and follows the aircraft on its assigned
path until the Instrument Landing System (ILS) takes over and sets it down on the
Since pilots can't just step on the brake and slow down, the problem is complicated
by faster planes overtaking the slower ones. A fast plane coming in later might
wind up right on top of a slower plane that had already started its landing approach.
Hence, not only the sequence of the incoming aircraft but also their speeds must
be taken into account. This adds to the space demand of fast planes and to the score
of factors that every minute may tip the balance of life and death at a busy airport.
Volscan keeps all these factors "in mind" at any moment, and automatically parcels
out to each plane precisely the air space it needs to keep that fateful balance
firmly held down on the safe side. As the airport radar sweeps the sky, each plane
in the area appears as a "blip" on the radar screen. The operator marks each newly
appearing blip with a light gun, which triggers Volscan's electronic brain into
action. The computer then "follows" the plane as the blip moves on the radar screen.
Acting as an electronic traffic manager, the computer has stored within itself
the correct answers to every possible landing approach situation that may arise.
Since the computer has the answer before the problem actually comes up, it needs
only a fraction of a second to pick the correct approach instruction - in effect,
to assign a block of space. These instructions are then given to the pilot by radio,
or fed directly into the airplane's automatic controls by data-link transmission.
Always on guard against error, Volscan keeps its unblinking eye on up to 14 planes
which it guides simultaneously. If either the human or the automatic pilot takes
any plane off the assigned course, the computer immediately compensates for the
mistake and issues new instructions for getting the plane back on its track and
arrival schedule. It must "touch down" at just the right moment, for the 13 other
planes are strung by the computer in a tight but safe landing sequence. The result
is maximum use of the available runway facilities, increasing the safe traffic capacity
of any airport almost three times.
In this manner, Volscan can handle one landing every 30 seconds, thus reducing
the dangerous practice of "stacking" airplanes waiting around an airport for an
opportunity to land. Such stacking is discomforting in present-day planes, but for
the jets of the not-distant future, it would be disastrous. For jets use almost
three times as much fuel at approach altitude as they do at cruising altitude. While
awaiting their landing clearance, they might exhaust their fuel reserve.
Volscan and the whole problem of air traffic control point up those ironic twists
by which history bedevils human effort. Fifty years ago, when Man first transformed
himself into a creature of flight, the main idea was to get him off the ground.
Now, in the headlong progress of the air age, he seems to have trouble in getting
down again. But electronics offers him a safe ladder for his descent.
Posted April 18, 2022
(updated from original post on 6/30/2016)