Aviation Hot air balloon in Hünenberg ZG caught fire due to leaking gas

The Swiss Transportation Safety Investigation Board (Sust) has clarified the cause of a hot-air balloon that caught fire in Hünenberg ZG in June 2023. Due to a technical defect, liquid gas sprayed onto the wicker basket, which ignited shortly afterwards.

The liquid escaped when the pilot tried to disconnect the filling bottle from the balloon's fuel system after take-off, the Sust wrote in its final report on Wednesday. He then attempted to close the rotary coupling of the fuel hose of the filling bottle, but was unable to do so.

According to Sust, the cause of the fire was due to the "improper" loosening of the filling bottle and a defective non-return valve on the connection of the filling bottle's fuel hose.

After the fire broke out, the pilot tried to prevent the balloon from taking off by releasing the hot air. At the same time, he ordered the first three passengers to disembark. The balloon then climbed up to the treetops. After continuously releasing the air, the balloon was finally prevented from rising any further.

Six of the seven passengers were injured in the accident. One person suffered serious injuries. The pilot's wife drove the passengers to Zug Cantonal Hospital. The hot-air balloon burned except for a small part of the envelope.

SDA