What happened
On the evening of April 28, 1998, a passenger hot air balloon flight experienced a serious incident near the Loosdrechtse Plassen. The aircraft, a Cameron Grolsch-105 with registration PH-GBF, was performing a landing maneuver when it encountered the influence of a localized storm area.
As the balloon approached the landing site, the pilot encountered a sudden change in wind direction and speed. To avoid colliding with nearby houses, the pilot was forced to use the burners. This action, combined with the arrival of a cold air mass associated with the approaching storm, caused the balloon to enter an uncontrolled ascent, climbing at approximately 1,000 feet per minute.
Because the aircraft was a "special shape" balloon, it lacked a traditional parachute valve. The pilot attempted to use the dump valve and eventually partially opened the rip panel to induce a descent. However, because the rip panel cannot be resealed once opened, the descent became difficult to manage. The balloon eventually descended at a rate of roughly 300 feet per minute and landed in the water. All three occupants (one pilot and two passengers) were rescued from the water by a passing boat.
The investigation
The investigation examined the meteorological conditions, the aircraft's technical capabilities, and the pilot's decision-making process. Investigators reviewed weather reports from Schiphol, which had indicated a low probability of significant storms, and noted that other balloonists in the region had flown successfully earlier that evening.
Technical analysis focused on the specific design of the PH-GBF. Unlike standard balloons, this special-shaped model relies on natural cooling and uses a dump valve rather than a parachute valve. The investigation also reviewed the use of the rip panel, noting that while the flight manual permits its use in emergencies up to 15 meters above the ground, the pilot utilized it at a much higher altitude to avoid the approaching storm and the Schiphol CTR.
Findings
- The primary cause of the incident was the encounter with a storm cell that brought sudden changes in wind speed and direction.
- The presence of a cold air mass ahead of the storm caused the balloon to rise rapidly as the heated air inside the envelope became much warmer than the surrounding environment.
- The aircraft's design provided limited ability to control ascent rates compared to conventional balloons, as it lacked a parachute valve.
- The pilot's decision to use the rip panel was a calculated risk taken to avoid an uncontrolled ascent into a more dangerous weather system, though it resulted in a difficult-to-manage descent rate.