What happened
On October 18, 1997, a Wörner K - 1000/3-STU gas balloon was participating in a competitive flight starting from Bitterfeld. The flight, which included the pilot and three passengers, was heading toward a target area near Fehrbellin. During the flight, the balloon descended to an altitude of approximately 20 meters as it entered the fenced operational area of a high-power shortwave transmitter station near Nauen.
As the balloon passed near the transmitter''s antennas, it entered the maximum radiation zone of Antenna 2. Shortly after passing the antennas, the balloon began to ascend. Witnesses observed smoke developing at the top of the envelope. At an altitude of approximately 180 meters, the balloon's net separated from the envelope, causing the basket to plummet into a ditch. The hydrogen-filled envelope continued to rise, eventually exploding at an altitude of 300 to 400 meters. The impact of the basket resulted in four fatalities.
The investigation
The BFU investigation focused on the interaction between the aircraft's components and the electromagnetic field of the transmitter. Investigators examined the wreckage of the Wörner K - 1000/3-STU, including the specialized materials used in the balloon's construction. The investigation analyzed the flight path, meteorological conditions, and the physical properties of the net's synthetic fibers. No technical defects were found in the aircraft's mechanical components, and the weather conditions were determined to be favorable for flight.
Findings
- The balloon entered the fenced transmitter facility at a dangerously low altitude, failing to maintain the required safety altitude of 150 meters.
- The aircraft passed within 100 meters of Antenna 2, exposing it to an electromagnetic field strength exceeding 200 V/m for approximately 26 seconds.
- The electromagnetic field caused steel-fiber filaments embedded in the polypropylene net to react, creating an ignition source.
- This ignition ignited escaping hydrogen gas, leading to multiple fire points on the envelope.
- The resulting fire damaged the net at the crown, causing the separation of the envelope from the basket.