History of the Flight
The helicopter, a Bell 206L-1 registered N206DD, was conducting a coastal sightseeing tour from Beef Island airport in the British Virgin Islands with six passengers and one pilot. While flying at approximately 300 feet near the northwest shoreline of Virgin Gorda, the pilot observed the left fuel boost pump low pressure warning light illuminate. Resetting the circuit breaker had no effect, and about ten seconds later, the right fuel boost pump warning light also illuminated. The fuel gauge indicated approximately 150 lbs, then quickly rose to 350 lbs for roughly five seconds. The low fuel level warning light was not seen. Approximately 15 seconds after the first low fuel pressure indication, the engine stopped. The pilot entered autorotation from about 200 feet and glided toward the shore. The helicopter landed in a level attitude on water, but despite deployment of skid-mounted flotation bags, it rolled onto its right side in about three feet of water. All passengers were uninjured and exited through the left side doors to wade ashore.
Fuel System Description
The Bell 206L-1 Long Ranger fuel system includes a main fuel tank integral with the rear passenger bench seat, with two additional fuel tanks located beneath the forward seats. Main tank capacity is 76 US gallons; each forward tank holds 11 US gallons, for a total of 98 US gallons. N206DD had a range extender modification increasing total capacity to 110 US gallons. Fuel transfers from each forward cell to the main tank via a dual-element ejector pump powered by fuel from the left and right fuel boost pumps. Loss of fuel flow is indicated by boost pump warning lights. Fuel quantity is measured by capacitive sensors and displayed on a single gauge.
Wreckage Examination
Examination by a manufacturer’s representative found no pre-impact problems with dynamic components. Water was present in the engine nozzle fuel line and airframe filter. The airframe fuel filter was only 20% full of liquid, whereas it is typically found full under normal circumstances. It was unknown whether water ingress occurred as a result of the accident. No breaks were observed in the lines and fittings. A significant amount of contamination was found in the left side inline fuel transfer filter. The contamination included paint flakes and fragments of thin transparent plastic-like sheet material, up to 0.25 inches in size. The amount of debris likely caused fuel to bypass the filter screen at some point, but no debris was seen in the ejector pumps downstream of the filters. The presence of debris in other parts of the fuel system was not determined. The refueling method for this helicopter was not established.
Discussion
The manufacturer's investigator opined that sufficient debris obscured the left jet pump supply filter mesh, causing fuel to flow through the bypass. It appears likely that debris obstructed the left side of the dual-element jet pump, interrupting fuel transfer from the forward tanks to the main tank. The simultaneous illumination of both boost pump warning lights suggests the main tank became exhausted, consistent with the subsequent engine stoppage. The cockpit gauge showing approximately 150 lbs of fuel remaining indicates the forward left tank was nearly full, i.e., fuel had not transferred. The low fuel level warning light should have illuminated with about 10 gallons remaining but was not seen by the pilot; no explanation was found for its absence.