What happened
On July 23, 2021, a Balóny Kubíček BB 37N hot air balloon was conducting a flight near Kerspenhausen, Germany. During the flight, the balloon ascended to a maximum altitude of 4,290 m AMSL. While climbing near a wind farm, the pilot observed what he perceived to be a suction effect from the turbines and initiated a rapid ascent to avoid them. During this climb, the burners caused heat damage to the envelope, and a structural line became detached from its loop.
As fuel supplies depleted, the pilot began a descent. To conserve the remaining fuel, the pilot performed a cold descent, which resulted in a high vertical sink rate of approximately 6 m/ 2s. The balloon struck a rapeseed field at a high velocity. The impact was so severe that two passengers were thrown from the basket, and the pilot also fell out. The basket briefly lifted off the ground and traveled approximately 80 meters before coming to a final rest. The incident resulted in one pilot with minor injuries, two passengers with serious injuries, and two passengers with minor injuries.
The investigation
The BFU investigation examined the flight data, meteorological conditions, and the pilot's preparations. Investigators analyzed flight path data from a passenger's smartwatch, which confirmed the high sink rate during the final phase of the flight. The investigation also reviewed the pilot's weather briefing, which was found to be outdated and focused on the wrong geographic area, and evaluated the technical condition of the BB 37N envelope, burners, and basket.
Findings
- The primary cause of the accident was that the balloon was not arrested in time during a high-rate cold descent, leading to a hard landing.
- The pilot experienced a loss of situational awareness, evidenced by the failure to properly monitor wind conditions and the delayed attempt to arrest the descent.
- Inadequate meteorological preparation meant the pilot was unaware of a favorable southeasterly wind layer that could have allowed for a safe passage around the wind farm.
- The rapid ascent to avoid the wind turbines prevented the pilot from effectively sensing wind changes at different altitudes.
- The pilot was operating the balloon for commercial purposes without a valid proficiency check.
- The flight entered Class C airspace without the required air traffic control clearance or a transponder, making the balloon invisible to air traffic services.
- The pilot ascended to an altitude exceeding 4,000 m AMSL without the required supplemental oxygen supply for the occupants.