Ultramagic S-160 N30048 accident near Rancho Santa Fe, California

Probable cause

A reduction of burner/heat production due to low fuel. Contributing to the accident was the pilot's continued flight with a low fuel status.

NTSB analysis

The pilot reported that as the air tour balloon flight progressed, the wind moving the balloon gradually dissipated to a calm state. He stated that to reach his selected landing site, he needed to cross over some high power transmission wires; however, the balloon's three burners failed to produce full power and he elected to land short of the transmission wires. He performed an emergency descent by pulling the top out of the envelope and subsequently, the balloon landed hard. During the landing, three passengers were injured, and the envelope snagged on several trees resulting in substantial damage to the envelope. According to the pilot, at the time of the landing, each of the three 20-gallon fuel tanks was approximately 15 to 20 percent full. A balloon repair station owner reported that burner utilization during flight is either FULL on or totally off (except for the pilot light). When the fuel level of a tank is between approximately 10 to 20 percent, the liquid propane will begin to cavitate in a vortex manner due to the rapid evacuation of fuel through the fuel tank's liquid dip tube, which supplies each respective burner via a fuel hose. When this occurs, there is a discernible difference in the sound of a burner, a pulsing woof-woof, and the power output/thermal output is dramatically reduced. The Flight Manual for the balloon stated in the landing section: "Burner, connect if possible to a fuel cylinder filled to at least 40 percent of its capacity." Additionally, the Flight Manual states "Any contact with electric power lines is extremely dangerous and should be avoided at all costs."

Text from the NTSB. Open the NTSB docket for WPR10LA169 for the full record.