Accident Overview
On August 14, 2017, about 0633 Alaska daylight time, a Cessna T207 airplane, registration N745KP, sustained substantial damage when it was involved in an accident near Juneau, Alaska. The pilot and four passengers were not injured. The airplane was operated by Alaska Seaplanes as a Title 14 Code of Federal Regulations Part 135 scheduled commuter flight.
Flight Details
According to Alaska Seaplanes dispatch documents, the accident flight was scheduled to transport passengers from Haines Airport and Skagway Airport to Juneau Airport. The pilot stated that during his preflight inspection, he measured fuel levels with a calibrated dipstick: the right tank contained 26 gallons and the left tank contained 11 gallons. Fuel samples from both wing tanks and the gascolator were clean. The flight departed Haines at about 0530 with one passenger, then picked up three more passengers at Skagway, departing at 0547. The pilot selected the right fuel tank for the entire 0.9-hour flight.
Emergency Landing
During the approach, about 3 miles from the runway at an altitude of about 900 ft, engine fuel flow reduced to almost zero and the engine lost all power. The pilot switched the fuel selector to the left tank and turned on the auxiliary boost pump, but engine power was not restored. He ditched the airplane near the southeast corner of Coghlan Island. After landing, the airplane remained upright; the pilot and passengers evacuated through forward doors and a rear door, swimming about 80 ft to shore. Neither the pilot nor passengers donned life vests due to limited time. The airplane sank in about 70 ft of water.
Post-Accident Examination
The airplane was recovered that evening and transported to a secure facility at Juneau Airport. The left wing and fuselage sustained substantial damage. Under the supervision of an FAA safety inspector, fuel tanks were drained: 2 gallons of 100 low-lead aviation fuel from the right tank system and 13 gallons from the left. Examination of the fuel system revealed moderate wrinkling of both fuel bladders, with more extensive folds in the right tank. Fuel screens were clear, quantity senders intact, wing vents clear, vented fuel caps secure and functional. The fuel selector valve operated normally; the auxiliary fuel pump pressurized fuel at the injectors. No fuel leaks were observed.
The engine was intact and attached to the airframe. Control continuity was established at throttle and mixture levers. Borescope examination showed normal combustion signatures; sparkplugs had saltwater contamination and normal wear. No spark was produced from either magneto until the ignition harness was replaced. The throttle body/fuel metering valve had a small amount of debris. When the boost pump was activated, fuel injector lines ejected water then fuel flowed freely. About 5 gallons of recovered fuel was poured into the right tank, and the engine started successfully, running normally at idle, high power, and during rapid accelerations.
Fuel System Issues
The airplane was equipped with two 40-gallon long-range tanks with 36.5 gallons usable fuel in all conditions. The pilot used a fuel consumption rate of 18 gallons per hour for planning; manufacturer's data showed 16.4 gph at sea level. The pilot planned a 0.7-hour flight with 1.5 hours of fuel in the right tank, expecting 13-15 gallons remaining. However, flight time was 0.9 hour, so about 10 gallons should have remained in the right tank, but only 2 gallons were drained after the accident. The left tank contained 13 gallons, 2 more than measured at departure. It could not be determined whether fuel leaked through the vent system while submerged.
Company pilots stated that the airplane’s fuel quantity indicators were unreliable, and company policy required using the dipstick. The pilot noted both fuel indicators showed about 1/2 full when power was lost. Pilots reported a history of loss of engine power due to fuel exhaustion, with three other events in the previous year. Some events were not reported. One pilot reported that the left tank sometimes had more fuel than expected and the right tank less. A week before the accident, a similar loss of power occurred at 300 ft over water after takeoff; power was restored by selecting the left tank and turning on the auxiliary pump. On that occasion, the right tank had only 5 gallons when it should have contained 12. Maintenance inspections found no anomalies.