What happened
On March 5, 1973, at 12:52 UTC, an Iberia DC 9, registration EC-BII, and a Spantax Convair 990 (Coronado), registration EC-BJC, collided in the airspace near Nantes, France. The Iberia flight, operating as IB 504 from Palma to London, was cruising at flight level 290. The Spantax flight, operating as BX 400 from Madrid to London, was also operating at flight level 290.
At the time of the accident, a military replacement air traffic control system, known as the 'Clément Marot' plan, was in effect due to ongoing civil aviation strikes. The Spantax crew had been instructed to delay their arrival at Nantes by approximately eight minutes to maintain separation from the Iberia aircraft. To achieve this delay, the pilot of the EC-BJC initiated a 360-degree right turn. However, due to a lack of clear communication and the aircraft's position, the maneuver led the Convair 990 to cross the path of the DC 9.
The collision caused the DC 9 to disintegrate in flight, resulting in the deaths of all 68 people on board (7 crew and 61 passengers). The Convair 990 sustained severe damage, including the loss of a portion of its left wing near the engine mount. Despite the critical damage, the crew managed to perform an emergency landing at Cognac. All 97 people on board the Spantax aircraft (8 crew and 89 passengers) survived.