What happened
On May 10, 1999, at approximately 20:15 local time, a Cameron N-180 hot air balloon, registration PH-IAB, was being prepared for a passenger flight in Amersfoort, Netherlands. The crew and seven passengers were already inside the basket as the balloon was being inflated. Although the air temperature inside the envelope had not yet risen enough to provide sufficient lift for takeoff, a sudden gust of wind exerted significant force on the partially inflated balloon.
This wind gust caused the ground anchoring system to fail. Specifically, a nylon strap used to secure the balloon to the earth via a quick-release mechanism snapped. Once the tether broke, the wind dragged the basket and balloon across the terrain. The balloon was pushed upward by an updraft near a line of trees at the edge of the field, subsequently drifted over two buildings, and finally came to rest in an open area of the complex. The pilot sustained light injuries during the incident, while all seven passengers remained unharmed.
The investigation
The investigation focused on why the ground anchoring system failed despite the wind speeds being within the operational limits for the aircraft. While the maximum allowable wind for this balloon type is 15 knots, the pilot had checked the forecast, which predicted ground winds of no more than 12 knots.
Investigators examined the hardware of the quick-release mechanism and discovered that a sharp burr on the aluminum component of the system had acted as a cutting edge. Under the tension exerted by the wind gust, this burr sliced through the nylon strap.
Findings
- The primary cause of the accident was the failure of the ground anchoring strap due to a sharp burr on the aluminum quick-release hardware.
- The wind gust provided the necessary force to trigger the failure of the compromised strap.
- Previous similar incidents involving the loss of balloon moorings had occurred in the past.
Safety action
Following the accident, the pilot took steps to round off sharp edges on the quick-release systems of other balloons to prevent similar burr formation. The investigation concluded with a request for the Rijksluchtvaartdienst (National Aviation Authority) to notify users of the potential hazards associated with anchoring systems and the specific risk of burr formation on quick-release components.