N745KPCessna T207 · 1974

On August 14, 2017, about 0633 Alaska daylight time, a Cessna T207 airplane, 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 as a Title 14 Code of Federal Regulations Part 135 scheduled commuter flight.

According to Alaska Seaplanes (the operator) dispatch documents, the accident flight was scheduled to transport passengers from Haines Airport (HNS), Haines, Alaska, and Skagway Airport (SGY), Skagway, Alaska, to the company base at Juneau Airport (JNU), Juneau, Alaska. The pilot stated that, as part of his preflight inspection, he measured the fuel levels with a calibrated dipstick; the right tank contained 26 gallons and the left tank contained 11 gallons. He took fuel samples from both fuel wing tanks and the gascolator, which all produced clean, clear fuel. Company dispatch documents indicated that the flight departed HNS about 0530 with one passenger, and then flew to SGY, where three additional passengers boarded. The flight departed SGY at 0547 and flew toward JNU. The pilot stated that he had the right fuel tank selected for the entire 0.9-hour flight.

During the approach, about 3 miles from the runway at an altitude of about 900 ft, the engine fuel flow reduced to almost zero and the engine lost all power. The pilot stated that he switched the fuel selector from the right fuel tank to the left fuel tank and turned on the auxiliary fuel boost pump. Engine power was not restored, and the pilot ditched the airplane near the southeast corner of Coghlan Island. After the landing, the airplane remained upright, and the passengers in the front two rows and the pilot evacuated out the forward doors; the third row passenger evacuated out the right rear door and all swam about 80 ft to the shore. Neither the pilot nor passengers donned their life vests due to the limited time available. The airplane sank in about 70 ft of water.

The airplane was recovered from the seafloor later that evening and transported to a secure facility at JNU. The left wing and fuselage sustained substantial damage. The fuel tanks were drained of fuel and sea water under the supervision of a Federal Aviation Administration safety inspector. Two gallons of 100 low lead aviation fuel were recovered from the right tank system and 13 gallons from the left tank.

A detailed examination of the airplane fuel system revealed that both wing fuel bladders exhibited moderate wrinkling, with more extensive folds in the right fuel tank bladder. The fuel screens were clear, and the quantity senders were intact. The wing fuel vents were clear and the vented fuel tank caps were secure and functional. The fuel selector valve operated normally. The auxiliary fuel pump was tested, and pressurized fuel was noted at the fuel injectors. There were no fuel leaks observed.

The engine was intact and attached to the airframe. Control continuity was established at the throttle and mixture levers. A lighted borescope examination revealed normal combustion signatures at the valves, piston domes, and cylinder surfaces. The sparkplugs exhibited some saltwater contamination and normal wear signatures. No spark was produced from either magneto. Serviceable magnetos were installed and tested but did not produce spark until the ignition harness was replaced. The throttle body/fuel metering valve exhibited a small amount of debris. The fuel injector lines ejected some water when the auxiliary boost pump was activated, and then fuel was observed flowing freely through each injector line. About 5 gallons of recovered fuel was poured into the right fuel tank and the engine was started successfully. The engine ran with no anomalies at idle and high power settings, and during rapid power accelerations.

The airplane was equipped with two 40-gallon, long-range tanks with 36.5 gallons usable fuel in all flight conditions. The pilot used a conservative fuel consumption rate of 18 gallons per hour (gph) for fuel planning. The manufacturer's cruise performance chart at sea level indicated a fuel consumption of 16.4 gph at 2,500 rpm and a manifold pressure of 28 inches of mercury. The pilot planned on flying for 0.7 hour and departed with 1.5 hours of fuel (26 gallons) in the right tank. He expected that about 13 to 15 gallons of fuel would remain in the right tank after the flight. However, the flight time for the accident flight legs was 0.9 hour; based on this, about 10 gallons should have remained in the right tank; however, only 2 gallons was drained from the right tank after the accident, and the left fuel tank contained 13 gallons after the accident, which was 2 gallons more than the pilot reported that he measured at departure. It could not be determined whether fuel leaked through the vent system while the airplane was submerged.

Company pilots stated that the airplane’s fuel quantity indicators were unreliable, and the company policy was to use the calibrated fuel stick to confirm the fuel levels before each flight. The pilot stated that both the left and right fuel quantity indicators showed about 1/2 full when the engine lost power.

Company pilots stated during interviews that the airplane had a history of loss of engine power due to fuel exhaustion, which company management personnel and pilots attributed to poor checklist use, fuel mismanagement, or vapor lock. There were three other loss of power events in the previous year. Not all events were reported to management or maintenance. Some pilots reported that the fuel quantity in the right tank was often less than expected after flights. One pilot stated that the left fuel tank sometimes contained more fuel than expected after a flight and the right tank contained less than expected. A week before the accident, the airplane had a loss of engine power at 300 ft over the water after takeoff with passengers onboard. That pilot stated that power was readily restored once the left fuel tank was selected and the auxiliary fuel pump was turned on. He returned to the airport and observed that the right tank had only 5 gallons, when it should have contained 12 gallons. Maintenance personnel inspected the airplane after the reported events and found no anomalies.

According to the FAA Airplane Flying Handbook, vapor lock is a condition in which air enters the fuel system and it may be difficult, or impossible, to restart the engine. Vapor lock may occur as a result of running a fuel tank completely dry, allowing air to enter the fuel system. On fuel-injected engines, the fuel may become so hot that it vaporizes in the fuel line, preventing fuel from reaching the cylinders.