Investigation Summary
The accident took place during a period of industrial action by French civilian air traffic controllers. To maintain operations, the French government implemented the Clément Marot Plan, utilizing military controllers and facilities. These controllers were less experienced with high-density civilian traffic and operated under different procedural standards, such as requiring larger vertical separations which reduced available airspace. On the day of the accident, both aircraft were en route to London at FL290. The Spantax flight (BX400) was instructed to arrive at the Nantes VOR at 13:00, while the Iberia flight (IB504) was estimated there at 12:52. Because BX400 was ahead of schedule, the crew attempted to request a delay maneuver. Garbled radio transmissions and sector boundary handoff issues prevented clear communication with 'Marina' and 'Menhir' control sectors. Fearing they would arrive too early and violate their timing instruction, the Spantax crew initiated a 360-degree turn in cloud without a formal clearance. During this turn, they intersected the path of IB504.
Final Conclusions
The BEA concluded that the primary cause was the Spantax crew's decision to initiate a turn without ATC authorization, which brought them into conflict with the Iberia aircraft. However, the report heavily cited systemic failures: the military contingency plan created a source of conflict by assigning the same flight level to two aircraft arriving at the same point simultaneously. The reliance on time-based separation was inappropriate given the poor quality of air-to-ground communications and the lack of effective radar identification of the Spantax aircraft by the Menhir sector.
Video Analysis
Nantes Collision (1973) - The Catastrophe Caused by a Strike — An analysis of how a series of systemic failures and a civilian ATC strike in France led to a mid-air collision between two Spanish airliners.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Iberia IB504 — McDonnell Douglas DC-9-32 · EC-BII
Spantax BX400 — Convair 990-30A-5 Coronado · EC-BJC
Crew Experience
Captain
First Officer
Pilot under training
Víctor José Alcubierre Camacho
Captain
First Officer
Flight Engineer
Systems & Failure Modes
Clément Marot Plan
The French military contingency plan designed to manage civilian airspace during ATC strikes.
VOR (VHF Omnidirectional Range)
The navigational beacon at Nantes served as the convergence point for the two airways involved.
TCAS
Traffic Collision Avoidance System; not available in 1973, its later development was influenced by accidents like this.
Interesting Facts
- 01The collision occurred at an altitude of 29,000 feet (FL290).
- 02French civilian air traffic controllers were on strike, and the airspace was controlled by the military.
- 03The Spantax Convair 990 landed safely with all 107 occupants surviving.
- 04The Iberia DC-9 was completely destroyed, resulting in the deaths of all 68 people on board.
- 05One of the fatalities on IB504 was Michael Jeffery, the former manager of Jimi Hendrix.
Safety Actions & Advisories
ATC Strike Procedures
The accident highlighted the dangers of using military controllers for high-volume civilian traffic, leading to reviews of contingency planning and international pressure on France regarding ATC labor disputes.