What happened
On December 24, 2008, a Cessna 208B, registration N21070, departed St. John's, Canada, on a delivery flight destined for Santa Maria, Azores. The aircraft was equipped with specialized Weaver Aero International auxiliary fuel tanks to facilitate the long-range Atlantic crossing.
Approximately three hours into the flight, while cruising near 40°W, the pilot identified an anomaly in the fuel transfer system. Specifically, fuel was no longer flowing from the auxiliary tanks into the main right fuel tank. Despite attempts to troubleshoot the electrical connections and the pumps, the pilot was unable to restore the flow. Realizing that the remaining fuel in the main tanks was insufficient to reach the original destination, the pilot declared a fuel emergency and requested a diversion to Flores Airport (LPFL).
The aircraft landed safely at Flores at 16:58 UTC. The following morning, after the aircraft was inspected, the fuel system was found to be operating normally, and the flight continued to its final destination.
The investigation
The GPIAAF investigation examined the aircraft's fuel system, the meteorological conditions during the flight, and the aircraft's exposure to freezing temperatures. The investigation noted that the aircraft had been parked outdoors in extremely cold temperatures prior to departure, which had previously caused ice to accumulate on the airframe.
Investigators analyzed the flight path, which took the aircraft through areas of moderate icing potential. The investigation focused on why the fuel transfer failed despite the pumps being functional and the electrical systems appearing operational.