What happened
On June 9, 2018, during a municipal festival in Argamasilla de Calatrava, Spain, an Ultramagic M-77 hot air balloon, registration EC-KEJ, was performing tethered (captive) flights. The flight involved the pilot, three children, and one adult.
While the balloon was only a few centimeters above the ground, wind instability caused the aircraft to touch the ground before rapidly ascending. During this sudden movement, one of the two windward anchor lines failed. This loss of stability caused the balloon to rise and drift laterally, eventually striking the cornice of a three-story building at an altitude of approximately 10 meters. The impact caused two panels on the lower part of the envelope to tear and dislodged a stone slab from the building's facade.
The investigation
The CIAIAC investigation examined the mechanical failure of the anchoring system and the meteorological conditions at the time of the incident. Investigators reviewed video footage of the flight, which showed the balloon destabilizing due to wind gusts.
The investigation focused on the specific failure of the carabiner used in the tethering setup. While the pilot was aware of wind forecasts near the operational limits, initial on-site measurements indicated lower wind speeds, leading to the decision to proceed. The investigation also reviewed the technical specifications of the hardware used to secure the balloon to the ground.
Findings
- The primary cause of the incident was the breakage of a carabiner that had shifted into a position where it was subjected to loads perpendicular to its longitudinal axis.
- While the carabiner had a longitudinal strength of 30 kN, its transverse strength was significantly lower, at only 9 kN.
- The sudden vertical and lateral tugging from wind gusts provided enough acceleration to exceed the reduced transverse strength of the hardware.
- The pilot and the operator, Club Deportivo Manchego de Aerostación María Luisa Cabañero, were operating within the general wind limits, though conditions were near the recommended thresholds for passenger flights.
- The impact resulted in two minor injuries among the passengers, while the pilot remained uninjured.