1976 Zagreb mid-air collision
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 Zagreb FIR in 1976, showing route of BA476 (red) and JP550 (green)
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| Summary | |
|---|---|
| Date | September 10, 1976 |
| Type | Mid-air collision |
| Site | over Vrbovec, Zagreb County, Yugoslavia |
| Total fatalities | 176 |
| Total survivors | 0 |
| First aircraft | |
| Type | Hawker Siddeley Trident 3B |
| Operator | British Airways |
| Tail number | G-AWZT |
| Flight origin |  London Heathrow AirportLondon, UK |
| Destination |  Yeşilköy Int'l AirportIstanbul, Turkey |
| Passengers | 54 |
| Crew | 9 |
| Survivors | 0 |
| Second aircraft | |
| Type | Douglas DC-9 |
| Operator | Inex-Adria Aviopromet |
| Tail number | YU-AJR |
| Flight origin |  Split AirportSplit, Yugoslavia |
| Destination |  Cologne Bonn AirportCologne, West Germany |
| Passengers | 108 |
| Crew | 5 |
| Survivors | 0 |
The 1976 Zagreb mid-air collision occurred on September 10, 1976 when British Airways Flight 476, a Hawker Siddeley Trident 3B en route from London Heathrow Airport to Yeşilköy International Airport, Istanbul, collided in mid-air with Inex-Adria Aviopromet Flight 550, a Douglas DC-9 en route from Split Airport, Yugoslavia, to Cologne Bonn Airport, West Germany, at 10:14 UTC. All 176 people aboard both flights were killed. The disaster is one of only two British Airways flights involving loss of life (the other being British Airways Flight 149, where one person was executed several hours after the Iraqi invasion of Kuwait).
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[edit] Introduction
In the mid-1970s, the Zagreb air traffic control region was one of the busiest in Europe despite being seriously undermanned and poorly equipped. The Zagreb VOR was a reporting point for a number of congested airways between northern Europe and southeastern Europe, the Middle East, and beyond. The airspace was divided into three sectors by altitude: the lower sector below 24,000 feet, the middle sector from 24,000 to 31,000 feet, and the upper sector above 31,000 feet.
[edit] British Airways Flight 476
British Airways Flight 476 departed Heathrow at 08:32 UTC as flight BEA476. At the controls of the Trident 3B was experienced captain Dennis Tann (born June 21, 1932), who by the time of the accident had accumulated 10,781 flying hours. He was assisted by first officer Brian Helm and acting first officer Martin Flint. The flight was uneventful until the aircraft reached the Zagreb VOR.
[edit] Inex-Adria Aviopromet Flight 550
Inex-Adria Flight 550 departed Split, Yugoslavia at 09:48 UTC bound for Cologne, West Germany as flight JP550. At the controls sat captain Jože Krumpak and first officer Dušan Ivanuš.
[edit] Air traffic controllers
At the time of the accident there were five controllers (and chief of shift) in Zagreb Area Control Center:
- Julio Dajčić, chief of shift (born 17 December 1932)
- Gradimir Tasić (born 29 April 1949), upper sector controller (at the time of the accident)
- Nenad Tepeš (born 2 September 1943), upper sector controller
- Mladen Hochberger (born 13 October 1946), currently president of the Croatian Air Traffic Controllers Union, upper sector controller
- Bojan Erjavec (born 15 June 1947), middle sector controller
- Gradimir Pelin (born 18 April 1948), middle sector controller
[edit] The accident
Flight 476 established contact with the Zagreb ACC upper sector controller Gradimir Tasić on 134.45 MHz at 10:04:12 UTC:
| 10:04:12 | BEA476 | Zagreb, Bealine 476, good morning. |
| Zagreb Upp | Bealine 476, good morning, go ahead. | |
| 10:04:19 | BEA476 | Er, 476, is Klagenfurt at 02, 330 and estimating Zagreb at One Four. |
| 10:04:27 | Zagreb Upp | Bealine 476, roger, call me passing Zagreb, flight level 330, Squawk Alpha 2312. |
| 10:04:38 | BEA476 | 2312 is coming. |
At the same time, JP550 contacted middle sector controller Bojan Erjavec asking for a higher flight level; the aircraft was at flight level 260, or 26,000 feet. FL280 and FL310 were unavailable, so Erjavec informed JP550 of the situation and offered FL350, which the pilots accepted.
To get clearance for a higher level, it was necessary to obtain the permission of the upper sector controller. Erjavec waved his hand to get Tasić's attention, but Tasić (who was working the upper sector on his own, as Hochberger gone to search for Tepeš) was far too busy to be interrupted. Pelin was then instructed to co-ordinate the climbout for the DC-9 with Tasić.
According to Pelin, he walked to the upper sector console holding JP550's flight progress strip. He asked Tasić if the DC-9 could climb to FL350. Tasić took the strip from Pelin and looked at it, then asked where the aircraft was at the moment. Pelin then pointed to a blip on the screen approaching Kostajnica. Tasić's response was 'yes, it could climb'. Pelin then noticed an aircraft on the screen coming from the direction of Metlika and asked Tasić about it, who said 'wait until they cross'. Pelin referred to the middle sector screen to make sure that he had identified the DC-9 positively on the upper sector screen. He then returned to Tasić and they both watched the targets pass each other, at which point Tasić authorized JP550 to climb. Pelin then called out to Erjavec and said 'yes, climb it'. Upon Erjevec receiving the OK from Pelin, he instructed the DC-9 to climb to FL350. That was at 10:07:40.
At 10:12:03, JP550 called the Zagreb middle sector controller to inform them that the aircraft was out of flight level 310. The last instructions given by Erjavec to JP550 were to call the upper sector controller on 134.45MHz and to stop squawking the assigned squawk code. By instructing JP550 to squawk Standby, Erjavec simply released a code allocated for the middle sector. The data tag for the DC-9 would now disappear from his screen and the aircraft would become merely a point among many others. If everything about this handover had been normal, the DC-9 would have been given a new code on initial contact with the upper sector controller and would have been positively identified on the upper sector screen with its flight number and altitude readout. But this had not been a normal handover because of the ill-handled coordination for the climb. Also, Tasić was busy with other traffic and JP550 did not immediately contact the upper sector controller. This could have been because the frequency was busy, but the pilots might also have delayed the call for some unknown reason.
At 10:14, JP550 contacted the upper sector controller as it was passing through 32,500 ft:
| 10:14:04 | JP550 | Dobar dan ["Good day"] Zagreb, Adria 550. |
| 10:14:07 | Zagreb Upp | Adria 550, Zagreb, dobar dan, go ahead. |
| 10:14:10 | JP550 | 325 crossing Zagreb at One Four. |
| 10:14:14 | Zagreb Upp | What is your present level? |
| 10:14:17 | JP550 | 327. |
The unmarked radar paint (or blip) representing JP550 was now merging with that of BEA476 over the Zagreb VOR. To convey the gravity of situation to the Slovene pilot as clearly as possible, Tasić spoke in Croatian:
| 10:14:22 | Zagreb Upp | [stammering] ... e... zadržite se na toj visini i javite prolazak Zagreba ["uh... hold yourself at this height and report passing Zagreb"]. |
| 10:14:27 | JP550 | Kojoj visini? ["What height?"] |
| 10:14:29 | Zagreb Upp | Na kojoj ste sada u penjanju jer... e... imate avion pred vama na... [not coherent] 335 sa leva na desno. ["The height you are climbing through because... uh... you have an aircraft in front of you at... [not coherent] 335 from left to right."] |
| 10:14:38 | JP550 | OK, ostajemo točno 330. ["OK, we'll remain precisely at 330."] |
As Tasić watched his screen, he saw the two paints merge, pass for a moment, and then vanish. He called out to BEA476 and asked it to report passing the next waypoint at Našice:
| 10:14:50 | Zagreb Upp | Bealine 476, Zagreb... report passing Nasice. |
| 10:14:56 | BE778 | Beatours 778, were you calling...? |
| 10:14:58 | Zagreb Upp | Negative. |
Tasić continued to call the two aircraft, ignoring calls from other aircraft:
| 10:15:50 | Zagreb Upp | Adria 550, Zagreb... |
| 10:16:00 | Zagreb Upp | Adria 550, Zagreb... |
| 10:16:14 | Zagreb Upp | Adria 550, Zagreb... |
| 10:16:32 | Zagreb Upp | Adria 550, Zagreb... |
| 10:16:42 | Zagreb Upp | Adria 550, Zagreb... |
| 10:16:50 | Zagreb Upp | Bealine 476, Zagreb... |
| 10:16:58 | Zagreb Upp | Bealine 476, Zagreb... |
The two aircraft had collided over the town of Vrbovec. The last 5 meters of the DC-9's left wing sliced through the Trident's cockpit section. The DC-9 went into an immediate nose dive; the Trident remained in flight for a short while before going down. All 63 people aboard flight 476 and 113 people aboard flight 550 were killed.
[edit] Trial
By noon that day, all controllers were in custody for interrogation. Later, all were released except Tasić, who remained in custody until the trial.
The trial opened on April 11, 1977 in Zagreb District Court. All the controllers were indicted under the Penal Code of Yugoslavia, Articles 271-72 as "persons who by endangering railway, sea or air traffic, threaten the lives of men or property".
Tasić was the only one to be found guilty; he was sentenced to seven years' imprisonment. After a petition by air traffic controllers, it was determined that Tasić had been used as a scapegoat, and he was released on November 29, 1978. He had served over two years and three months in prison.
[edit] References
- Richard Weston and Ronald Hurst, Zagreb One Four: Cleared to Collide?, 1982 (ISBN 0-246-11185-2)
- AAIB, British Airways Trident G-AWZT, Inex-Adria DC-9 YU-AJR: Report on the collision in the Zagreb area, Yugoslavia, on 10 September 1976 (Reprint of the report produced by The Yugoslav Federal Civil Aviation Administration Aircraft Accident Investigation Commission), Aircraft Accident Report 5/77
- AAIB, British Airways Trident G-AWZT, Inex-Adria DC-9 YU-AJR: Report on the collision in the Zagreb area, Yugoslavia, on 10 September 1976 (Reprint of the report produced by The Yugoslav Federal Committee for Transportation and Communications - Second Commission of Inquiry with United Kingdom Addendum), Aircraft Accident Report 9/82
