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, BX 400, was traveling from Madrid to London.
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 investigation established that the Iberia aircraft was following its assigned route at level 290. Simultaneously, the Spantax crew had been instructed to adjust their arrival time at Nantes to 13:00, but because their speed reduction was insufficient, the pilot initiated a 360-degree right turn to delay the arrival. This maneuver caused the Convair 990 to cross the path of the Iberia aircraft.
The collision occurred in very poor visibility. The DC 9 disintegrated in flight, resulting in the deaths of all 68 people on board (7 crew and 61 passengers). The Convair 990 suffered severe damage, including the loss of a portion of its left wing, but the crew managed to perform an emergency landing at Cognac. All 97 people on board the Spantax aircraft survived.
The investigation
The commission examined flight recordings, radar imagery from multiple sites (including Mont-de-Marsan, Brest, Tours, and Bordeaux), and radio communications. Investigators analyzed the coordination between the Marina and Menhir control sectors. The inquiry also reviewed the technical capabilities of the radar and radio equipment in use during the strike-induced replacement period.
Findings
- The primary cause of the collision was the unauthorized 360-degree turn by the Spantax crew, which placed the aircraft on a collision course with the Iberia flight.
- Air traffic controllers assigned the same flight level (290) to both aircraft for their arrival at Nantes at the same time.
- There was a significant lack of coordination between the Marina and Menhir control sectors; the Spantax aircraft was not properly identified on radar by the Menhir sector.
- Communication failures occurred because the Spantax pilot was not successfully transferred to the new frequency before entering the Menhir sector, leaving the crew isolated from controllers.
- The replacement control system lacked sufficient radar coverage and radio reliability to manage the increased complexity of the traffic.