1976 Zagreb mid-air collision

On 10 September 1976, British Airways Flight 476, a Hawker Siddeley Trident en route from London to Istanbul, collided mid-air near Zagreb, Yugoslavia (modern-day Croatia), with Inex-Adria Aviopromet Flight 550, a Douglas DC-9 en route from Split, Yugoslavia, to Cologne, West Germany. The collision was the result of a procedural error on the part of Zagreb air traffic controllers.

British Airways Flight 476
Inex-Adria Aviopromet Flight 550
Accident
Date10 September 1976
SummaryMid-air collision caused by ATC error
SiteNear Vrbovec, Yugoslavia
45°53′33″N 16°18′38″E
Total fatalities176
Total survivors0
First aircraft

G-AWZT, the aircraft involved, seen at Charles de Gaulle Airport approximately 3 months before the accident
TypeHawker Siddeley Trident 3B
OperatorBritish Airways
RegistrationG-AWZT[1]
Flight originLondon Heathrow Airport
London, United Kingdom
DestinationYeşilköy Int'l Airport
Istanbul, Turkey
Passengers54
Crew9
Fatalities63
Survivors0
Second aircraft

An Inex-Adria Douglas DC-9 similar to the aircraft involved
TypeDouglas DC-9-32
OperatorInex-Adria Airways
RegistrationYU-AJR
Flight originSplit Airport
Split, Yugoslavia
DestinationCologne Bonn Airport
Cologne, West Germany
Passengers108
Crew5
Fatalities113
Survivors0
Zagreb FIR in 1976, showing route of BA476 (red) and JP550 (green). Not to scale.

All 176 people aboard the two aircraft were killed,[2]:8[3]:5–6[4][5] making it, at the time, the world's deadliest mid-air collision.[6] It is the deadliest aviation accident in both Croatia and Yugoslavia.[7]

Flights

British Airways Flight 476 departed London Heathrow Airport for Istanbul Atatürk Airport at 08:32 UTC as flight BA476, with 54 passengers on board and a crew of 9.[3]:1 At the controls of the Trident 3B was an experienced captain, Dennis Tann (born 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.[3]:6–8

Inex-Adria Flight 550 departed Split Airport at 09:48 UTC bound for Cologne Bonn Airport as flight JP550. It carried 108 passengers, mostly German holiday-makers returning home at the end of a holiday on the Dalmatian coast, and a crew of 5.[3]:2 At the controls sat captain Jože Krumpak (born 1925), an experienced pilot with 10,157 flying hours, and first officer Dušan Ivanuš.[7][3]:10–11 Inex-Adria was a charter airline based in Slovenia, the northernmost of the constituent republics making up the federation of Yugoslavia.

Both flights proceeded uneventfully until they approached the Zagreb VOR.

Air traffic control

In the mid-1970s, the Zagreb air traffic control region was one of the busiest in Europe despite being seriously undermanned and poorly equipped.[8]:26 The Zagreb VOR was a reporting point for a number of congested airways between northern Europe and southeastern Europe, the Middle East, and beyond.[9] The airspace was divided into three sectors by altitude: the lower sector below 25,000 feet (7,600 m), the middle sector from 25,000–31,000 feet (7,600–9,400 m), and the upper sector above 31,000 feet (9,400 m).[3]:27–29

Accident

On entering Yugoslav airspace from Austria, BA476 established radio contact with the Zagreb ACC upper-sector controller Gradimir Tasić at 10:04:12 UTC, informing him that they were at Flight Level 330 (33,000 ft; 10,050 m) and expected to reach the Zagreb VOR at 10:14. The controller responded by instructing them to select transponder code 2312, and to call again on reaching the VOR:[3]:1

10:04:12BA476Zagreb, Bealine 476, good morning.
Zagreb UppBealine 476, good morning, go ahead.
10:04:19BA476Er, 476, is Klagenfurt at 02, 330 and estimating Zagreb at one four.
10:04:27Zagreb UppBealine 476, roger, call me passing Zagreb, flight level 330, Squawk Alpha 2312.
10:04:40BA4762312 is coming.

This was the last communication with the Trident aircraft before the accident.[3]:1

At around the same time, JP550 contacted middle-sector controller Bojan Erjavec asking for a higher flight level; the aircraft was at FL260 (26,000 ft; 7,900 m) . FL280 and FL310 were unavailable, so Erjavec informed JP550 of the situation and offered FL350 (35,000 ft; 10,650 m) , 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 co-worker Mladen Hochberger had gone to search for Nenad Tepeš, Tasić's replacement who was running late) was far too busy to be interrupted. Middle sector controller Gradimir 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 authorised JP550 to climb. Pelin then called out to Erjavec and said 'yes, climb it'. Upon Erjavec receiving the OK from Pelin, he instructed the DC-9 to climb to FL350. That was at 10:07:40.

Memorial to some of the dead

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 134.45 MHz 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 co-ordination 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.

By the time JP550 contacted the upper-sector controller at 10:14:04 it had reached the Zagreb VOR and was already climbing through FL325 (32,500 ft; 9,900 m) . The controller immediately asked for confirmation of the aircraft's level:[3]:4


10:14:04JP550Dobar dan ["Good day"] Zagreb, Adria 550.
10:14:07Zagreb UppAdria 550, Zagreb, dobar dan, go ahead.
10:14:10JP550325 crossing Zagreb at one four.
10:14:14Zagreb UppWhat is your present level?
10:14:17JP550327.

Realising the imminent danger of collision, Tasić instructed the JP550 to stop climbing. In doing so, he reverted to his native Serbo-Croatian language, contrary to the regulations.[3]:30 This meant that the British Airways plane, even if they overheard this conversation, would have very little chance of understanding their own imminent danger. The controller's last-ditch attempt to avert catastrophe turned what would have been a near miss into the collision he was trying to prevent. For, by the time JP550 had levelled off it was at flight level 330, exactly the same level as BA476:[3]:4

10:14:22Zagreb Upp[stammering] ... e... zadržite se na toj visini i javite prolazak Zagreba ["uh... hold your current altitude and report passing Zagreb"].
10:14:27JP550Kojoj visini? ["What altitude?"]
10:14:29Zagreb UppNa kojoj ste sada u penjanju jer... e... imate avion pred vama na... [not coherent] 335 sa leva na desno. ["The altitude you are climbing through because... uh... you have an aircraft in front of you at... [not coherent] 335 from left to right."]
10:14:38JP550OK, ostajemo točno 330. ["OK, we'll remain precisely at 330."]

The mid-air collision occurred at 10:14:41.[3]:1 Half a minute later, Tasić attempted to call BA476 and instruct it to report passing the next waypoint at Našice, but was answered by a different flight:

10:15:06Zagreb UppBealine 476, Zagreb... report passing Nasice.
10:15:12BE778Beatours 778, were you calling...?
10:15:14Zagreb UppNegative.

Tasić continued to call BA476 and JP550, ignoring calls from other aircraft, but to no avail:

10:15:50Zagreb UppAdria 550, Zagreb...
10:16:00Zagreb UppAdria 550, Zagreb...
10:16:14Zagreb UppAdria 550, Zagreb...
10:16:32Zagreb UppAdria 550, Zagreb...
10:16:42Zagreb UppAdria 550, Zagreb...
10:16:50Zagreb UppBealine 476, Zagreb...
10:16:58Zagreb UppBealine 476, Zagreb...

Meanwhile, a Lufthansa Boeing 737 was travelling eastbound on UB5 at flight level 290 towards Zagreb, only 15 miles behind the Trident. The co-pilot saw the collision as a flash of lightning and afterwards, out of a ball of smoke, two aircraft falling towards the ground. The Lufthansa captain, Josef Kröse, reported the sighting to Erjavec, the middle-sector controller.[10]

10:15:40Capt Kröse R/T....e Zagreb! It is possible we have a mid-air collision in sight. We have two aircraft going down, well, almost below our position now.

This was spoken in such an agitated voice that Erjavec was unable to understand what was being said. (Later, on hearing the recording of this call, Captain Kröse had difficulty in understanding his own words.) The Lufthansa captain had to repeat his message several times.

10:18:12Capt Kröse R/TIt is possible that the other aircraft ahead of us had a mid-air collision....er...just overhead Zagreb. We had two aircraft going down with a rapid rate of descent...and there was also smoke coming out.

When the implications of what was being said dawned on Erjavec, he glanced across to the upper-sector controller. At his station sat a stunned Tasić, white-faced with shock. Slowly he lifted the headset from his ears and placed it on the console in front of him.

The two aircraft had collided over the town of Vrbovec, northeast of Zagreb, the last five metres of the DC-9's left wing cutting through the Trident's cockpit section and forward passenger compartment.[3]:2,34 The explosive decompression caused the forward part of the Trident's fuselage to disintegrate; the Trident fell, landing on its tail and sliding a short distance before its remains came to rest. The DC-9, now without over one-third of its left wing, went into an immediate nose-dive and slammed into the ground right-wing first. In the end, everyone aboard both flights was killed.[11]

A police officer who was one of the first to arrive at the scene reported that a baby on the ground was "still giving feeble signs of life near the [British] plane, but even if the ambulances had arrived before me, it would have been too late to save it."[6]

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 11 April 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 persons or property".

Tasić was the only one to be found guilty; he was sentenced to seven years' imprisonment.[9] After a petition by air traffic controllers, it was determined that Tasić had been used as a scapegoat, and he was released on 29 November 1978. He had served nearly two years and three months in prison.

A dramatised reconstruction of the events leading up to the accident, starring Antony Sher and entitled Collision Course, was made by Granada Television in 1979.[12]

G-AWZT, the aircraft involved in the collision, at Edinburgh Airport in 1974 or 1975

The events of the accident are also documented in a season 1 episode of Aircrash Confidential titled "Collisions", which was first aired on the Discovery Channel in 2011.[13]

References
  1. "G-INFO Database". Civil Aviation Authority.
  2. "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. Yugoslav Federal Committee for Transportation and Communications (9/82). Retrieved 27 July 2011 – via Air Accidents Investigation Branch.
  3. "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. Yugoslav Federal Civil Aviation Administration Aircraft Accident Investigation Commission (5/77). 25 December 1976. ISBN 0-11-511809-8 – via Air Accidents Investigation Branch.
  4. Ranter, Harro. "ASN Aircraft accident Hawker Siddeley HS-121 Trident 3B G-AWZT Vrbovec". aviation-safety.net. Aviation Safety Network. Retrieved 28 June 2020.
  5. Ranter, Harro. "ASN Aircraft accident McDonnell Douglas DC-9-32 YU-AJR Vrbovec". aviation-safety.net. Aviation Safety Network. Retrieved 28 June 2020.
  6. "DISASTERS: Look Up in Horror". TIME. 20 September 1976. Retrieved 19 June 2011.
  7. "Tajna leta JP550" [Secret flight JP550]. Jutarnji list (in Croatian). 9 September 2006. Archived from the original on 7 September 2012. Retrieved 19 June 2011.
  8. Weston, Richard; Hurst, Ronald (1982). Zagreb One Four: Cleared to Collide?. HarperCollins. ISBN 0-246-11185-2.
  9. "Special Report: British Airways Flight 476". Airdisaster.com. Archived from the original on 13 April 2015. Retrieved 28 June 2020.
  10. Stewart, Stanley (1994). Air disasters. Enderby: The Promotional Reprint Company. p. 142. ISBN 1-85648-182-4.
  11. "Još sanjam kofere kako padaju s neba" [I still dream of suitcases falling from the sky]. Jutarnji list (in Croatian). 30 August 2008. Retrieved 4 May 2017.
  12. "Collision Course (1979)". bfi.org.uk. British Film Institute. Retrieved 28 October 2019.
  13. Barrett, Mathew; Griffiths, Alan; McNab, David; et. all (2011). Prince, Stephen; Gilbert, Roy (eds.). Aircrash Confidential (TV Documentary) (Collisions ed.). Discovery Channel: MMXI World Media Rights Limited; WMR Productions; IMG Entertainment.

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