Report: British Airways Flight 476
In the last 30-some years, air
traffic over Zagreb, Yugoslavia has been an increasing nightmare for the
operators of the Zagreb Air Route Traffic Control Center (ARTCC). Since the
end of World War II the majority of flights between Europe and the Far East
have been routed south around Yugoslavia to skirt the Eastern Bloc nations,
and the growth of popular holiday travel since the 1960s has meant that traffic
between northern Europe and the eastern Mediterranean has also passed directly
over the Zagreb beacon.
|One of the few existing photos of the Zagreb crash investigation hangar (File Photo).
As a result, by 1970, five high
level airways crossed the region, three of them, Upper Blue 5 (UB5), Upper
Blue 9 (UB9) and Upper Red 22 (UR22) intersecting directly over Zagreb. Upper
Blue 1 (UB1) ran slightly to the south, and the fifth airway, Upper Amber
40 (UA40) originated at Zagreb on a direct route to Sarajevo.
In the first five years of the
decade, 760,000 aircraft movements were handled by Zagreb ARTCC, and by 1976
the Zagreb ARTCC was the second busiest in Europe, its staff of 30 desperately
coping with traffic which required at least double their number. In 1973,
a modern radar flight control system was installed, but had teething problems,
and three years later was still being used only as back-up. Zagreb ARTCC
still relied on procedural control with pilots transmitting their positions
at specified points along the airways, these positions then being monitored
by the radar system.
Despite the staff shortage and
increased workload, Zagreb's safety record was, under the circumstances,
surprisingly good, although 32 air misses had been reported in the past five
years and two controllers had been dismissed for negligence. Even the negligence
charges came out not through lack of skill but from underwork: lateness for
duty and unauthorised absence from the control station to snatch a bite to
In September 1976, the Zagreb
ARTCC was working on a knife edge of nerves. At 08.32hrs GMT (09.32hrs local
time) on the morning of 10th September, British Airways scheduled
flight BA476 from London to Istanbul took of from Heathrow Airport, London.
Captain Dennis Tann commanded the Trident 3B, registration G-AWZT, with First Officer Brian Helm as
co-pilot and First Officer Martin Flint in the P3 position. Six cabin crew
attended the 54 passengers in the half-full aircraft for the three and a
half hour flight to Turkey.
BA476 was routed outwards over
Dover and onto Brussels and Munich. After reporting its position to Munich,
the aircraft settled on airway Upper Blue 1 (UB1), flying at 33,000ft (330)
and crossed into Austrian Airspace at 09.48hrs GMT.
At exactly that time, in the holiday
resort of Split, on the Yugoslavian coast, Flight JP550, a DC-9 of the Jugoslav
charter airline Inex Adria Aviopromet, took off on the journey to Cologne.
Two pilots, Captain Joze Krumpak and First Officer Dusan Ivanus were at the
controls of the DC-9, registration YU-AJR, while behind
them in the cabin three stewardesses coped with the demands of the 108
passengers. All but one of them were West Germans taking the two and a half
hour journey home.
bound Trident and the north-west bound DC-9 were both flight-planned to traverse
the Zagreb beacon. The airspace over Zagreb was divided into three layers
- lower, middle, and upper - with the middle and upper directed in the
short-staffed ATC center by a controller, where ideally three personel -
radar controller, procederal controller, and assistant controller - would
over Zagreb to its planned flight level of 310, would pass through the middle
control layer (from 25,000 to 31,000ft) at level 330.
GMT (11.00hrs local time) the duty shift which started at 07.00hrs local
at Zagreb ARTCC, had already been on station for four hours under its supervisor,
43-year-old Julije Dajcic. Dajcic's five-man team normally worked a 12-hour
duty day, with two hours at a control station controlling the upper and middle
layers of airspace, followed by a one-hour break.
who had been at his station for an hour, controlled the middle section console
with his assistant Gradimir Pelin, newly on duty. Mladen Hochberger controlled
the upper section and was due, at that moment, to be relieved by Nenad Tepes,
who had not so far appeared in the building and looked like being late.
Hochberger's assistant was 28 year old Gradimir Tasic, who had been on duty
for three and a half hours, the first two as duty controller. When Tepes
arrived, Tasic was due to continue for a further hour as his assistant,
monitoring procedures and co-ordinating flights with other regions on ground
telephone links. Tasic, the youngest member of the Zagreb staff, was on his
third consecutive day of 12-hour duty; all the others had taken at least
was developing into a busy one. Amongst other difficulties, Flight JP550,
planned to reach level 310 in a smooth climb out of Split, was tiptoeing
up the lower flight levels, on instruction from Zagreb, because levels above
260 were blocked by an east-west flow of traffic. Captain Krumpak, in the
Cologne bound DC-9, estimated Zagreb at about 10.16hrs; at 10.02 he radioed
passing level 220 and was instructed to transmit his next call on Erjavec's
middle sector frequency. A minute later he did so, and was allocated a radar
indentification "squawk" code, Alpha 2506.
At the same
time, Flight BA476 was crossing the Austrian-Yugoslavian border on flight
level 330, airway UB5, and was switched from Vienna control to Zagreb. The
call was taken by Tasic, who was now alone at the upper level console. Controller
Hochberger had impatiently left his seat to look for Tepes, the late
squawk Alpha 2312 to the Trident, with a continued flight level of 330. A
glance at his radar screen showed BA476's flight label to be either level
332 or 335, but the radar at Zagreb was known to be imprecise. Tasic ignored
it in order to send a Turkish aircraft at level 350 on its way. Someone on
BA476's flight deck exclaimed "there he is," as the Turkish aircraft passed
over them. Tasic now required clearance from Belgrade for an Olympic Airways
flight to Sarajevo on UB1 eastbound. He made a ground telephone call of some
25 seconds to clear this and a German aircraft, with an Iran Air flight close
on their heels.
Erjavec, at the middle control console, had JP550 at level 260. Captain Krumpak
asked for clearance to a higher level. Erjavec checked the levels available:
" Are you able to climb maybe to 350?", "Affirmative, affermative,
" replied Krumpak. "With pleasure." "Roger. Call you back." It was
In the corridor
outside the control rooms, Supervisor Hochberger had met his overdue replacement,
Tepes, and was deep in conversation with him. Through the glass windows,
Erjavec could see Tasic. To move JP550 to the upper level, he needed conformation
from either Hochberger or Tasic. He waved to Tasic through the glass, and
Tasic impatiently waved him away. Pelin, Erjavec's assistant, went around
to the busy Tasic's radar screen and indicated JP550's target, which was
unlabelled, and asked Tasic for clearance. Tasic, speaking into his headset,
simply thought an aircraft near Kostajnica was being indicated, and nodded
impatiently. Pelin assumed clearance had been recieved. It was a disasterous
BE476 was cruising at flight level
330 with a true airspeed of 480kt, though a tailwind pushed it to a groundspeed
of 489kt. The Trident had tracked a little to the south, and at 10:11:41
Captain Tann made a six degree left turn to home directly over the Zagreb
beacon, estimated at 10:14hrs. At the same time, the DC-9 was at level 310,
passing into the upper
At 10:12:06hrs, Erjavec bade Captain
Krumpak goodbye, instructing him to squawk "standby" on his transponder,
in order to release his middle section squawk code - 2506 - for another aircraft.
This was the second mistake, for though the radar was programmed to show
the flight label of any aircraft crossing into the upper section while
transmitting a middle section code, the "standby" squawk would not register
in the upper console. Hastily, Pelin altered the written strip showing JP550's
details for the planned middle sector and handed it to Tasic, but the harassed
controller had barely time to glance at the details. Virtually unannounced,
JP550 appeared on Tasic's radar screen as an unlabelled target.
At that moment, Nenad Tepes, the
latecomer, arrived at Tasic's elbow; as duty controller he was impatient
to vacate his seat, but for the moment Tasic was still busily directing flights.
He began trying to brief Tepes on the situation, which was reaching saturation
point: there were 11 aircraft now in the upper sector. Tasic still had not
had the time to examine JP550's flight details progress strip. In any case,
Pelin, in his own haste, had ommited to indicate with an arrow the fact that
the DC-9 was still climbing. Tasic was unaware of its height. In fact JP550's
rate of climb and true ground speed of 470kt would mean that it crossed Zagreb,
still climbing, at 10:14hrs - the same time as BA476.
Tasic's first verbal contact with
JP550 came at 10:14:04. Captain Krumpak said, "Dobar dan, Zagreb," or "Good
morning." Then: "three two five crossing Zagreb." The DC-9 was directly over
the beacon, 500ft below the Trident, still climbing, and the two aircraft
were still closing at a combined airspeed of 920kt - 1,100mph - faster than
a high velocity rifle bullet.
A frantic glance at his faulty
radar screen showed BA476's flight level, incorrectly, at 335. Tasic reckoned
that if he could hold the DC-9 at 327 they would whisker each other with
800ft to spare. Breaking into Croatian, Tasic begged Captain Krumpak to hold
his present height. Krumpak replied in their usual native
"OK. We'll remain precisely at
330." The time was 10:14:38. Three seconds later the outer five meters of
the DC-9's port wing sliced through the Tridents flight deck, killing Tann,
Flint, and Helm instantly. As JP550's wing tore off, the two aircraft rolled
together and fell from the sky.
The DC-9's CVR caught F/O Dusan
Ivanus's last words, as he sat in the right hand seat behind his usless controls.
"We are finished," he said, "Goodbye. Goodbye."
The two aircraft struck the ground
about 4 miles apart near the town of Vrbovec, 16 miles north-east of Zagreb.
All 176 people aboard died. Seven months after the crash, on 11 April 1977,
the five Zagreb controllers, the shift supervisor and two senior officials
faced charges of criminal negligence - and up to 20 years of imprisonment
each. After much battling in court, Tasic was the only one to face the charges
and got 7 years prison. After an appeal it was cut in half, then following
a petition he was released. Investigators found that all the controllers
had to cope with impossible situations using old equipment.