Mid-air Crash Over Zagreb Kills 176By Patrick Mondout
On September 10, 1976, an overworked Yugoslavian air traffic controller
(ATC) failed to keep track of an Inex
Adria DC-9 and a British
Airways Trident 3B over Zagreb
resulting in a collision and the deaths of all 176 aboard both planes in
the worst ever mid-air collision (the death count would be surpassed
in 1979).
The British Airways Trident was carrying 54 passengers and a crew of
nine from London to Istanbul while the DC-9 was heading to the Yugoslav
resort of Split to Cologne with a crew of five and 108 Germans on holiday.
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Inex
DC-9 |
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An Inex DC-9 similar
to the one involved in this crash, as seen in at
Gatwick in May 1983.
Image courtesy of AirNikon.
Find more of his photos at Airliners.net. |
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At 10:13:53, the first controller calls to the British plane, "Beatours,
maintain flight level 330 (33,000 feet) and report passing overhead
Zagreb. Squawk Alpha 2332." The request is acknowledged.
At 10:14:04, the Inex plane calls in and informs the second controller
they are, "325 crossing Zagreb at One Four." This means they
were crossing 32,500 feet and climbing.
The alarmed second controller ask the DC-9, "What is your present
level?"
At 10:14:17, the Inex crew responds, "327 (32,700 feet)."
At 10:14:22, the controller responds with "hold yourself at this
height and report passing Zagreb", hoping the two radar blips on his
screen, which are about to merge, will miss each other. The Inex asks,
"What height?"
At 10:14:29, the controller tells the Inex, "The height you are
climbing through because you have an aircraft in front of you at 335 from
left to right." The Inex crew responds with, "OK, we'll remain
precisely at 330 (33,000 feet)."
At 10:14:48, the points on his radar screen merged. He then called out
to the the Inex, but there was no response. The planes crashed near the
Vrolec Villlage near Zagreb, Yugoslavia (now Croatia).
The Trident was flying into the sunlight and the Inex plane was gaining
altitude. Both factors made it difficult for the Trident to spot the DC-9.
The controller was speaking in Croatian to the Yugoslavian plane, which
meant that the Trident crew was deprived of information that might have
saved their lives.
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British
Trident |
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This is the actual Hawker
Siddeley Trident 3B involved in this collision, as
seen at Heathrow in May 1974.
Image courtesy of John Stewart.
Find more of his photos at Airliners.net. |
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Ironically, if the controller had not asked the DC-9 to maintain it's
height, the accident would have been avoided; the DC-9 leveled-off before
colliding and actual was slightly higher than the Trident.
Five air traffic controllers and two supervisors were arrested but all
except one, Gradimir Tasic, were released. Tasic initially received a
seven year sentence, but it was released after air traffic controllers
around the world petitioned for his release.
While was Tasic was the controller responsible, he was working
short-handed that day (there should have been two controllers working his
sector).
Background
Commercial aircraft pilots do not just take any path that appeals to
them while they're flying. The are given (or request) vectors and
altitudes between locations which they are to stick to unless there is a
good reason and even then only with permission by the responsible ATC.
This is supposed to ensure aircraft maintain a minimum separation from one
another making collisions impossible.
It takes the human eye 1/10th of a second to see an object. It takes
about a full second to recognize the object and still more time to
recognize it's path and that it is a danger to you. Then your brain must
decide what to do and send signals to your muscles to guide your aircraft
out of the way. (Which direction are you going to turn? Are you going to
pull up or dive?) Your trusty aircraft is not a high-performance jet
fighter. It is a civilian passenger jet weighing about 200,000 pounds.
Imagine you have just determined that the DC-9 one mile (5,280 feet) in
front of you is a threat. One full mile. Seems like a lot, doesn't it?
However, the DC-9 is cruising at 580 mph and so are you. Thus, you are
closing in on one another at 1060 mph. You are now less than 3 seconds
from impact. Do you really think both you and your aircraft can react
sufficiently inside of three seconds to miss to the other aircraft? And
assuming you somehow manage to pull off the impossible with your aircraft,
what about the other aircraft? If that pilot does reacts at the same time
but in the same direction as you, you'll still collide.
As you can see, it is critical that ATC maintains proper separation
because at these speeds, it is too much to ask the crew to do so.
Source: Encyclopedia Britannica 1977 Yearbook.
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