WPR13LA396

The pilot's inadequate preflight fuel planning and poor decision-making, which resulted in fuel exhaustion and the subsequent loss of engine power. Contributing to the accident was the lack of documentation describing the limitations of the airplane’s fuel system.

The sport pilot was conducting a cross-country flight in the light-sport airplane, and he reported that he encountered strong headwinds during the flight. Concerned that the airplane's fuel level may be low, he landed at a private airstrip a few miles before his intended destination. He checked the fuel levels and estimated that there was enough fuel for about 30 minutes of flight. He chose to depart, and a few minutes after takeoff, the engine lost all power. He performed a forced landing into a field just short of the destination airport. The airplane sustained substantial damage during the accident sequence, and the pilot was not injured. Immediately following the accident, the pilot reported that the airplane did not have any mechanical malfunctions and that it ran out of fuel. Postaccident examination did not reveal any evidence of a preimpact engine malfunction or failure. Both fuel tanks were found intact and did not appear to be breached. The airplane's fuel system appeared to meet the light-sport airplane industry design standards for usable fuel, which are similar to the Federal Aviation Administration standards for certified aircraft. The pilot did not respond directly to multiple requests from the National Transportation Safety Board investigator-in-charge to answer questions regarding the specific accident circumstances. Therefore, the accident conditions could not be fully established. However, the pilot did provide multiple written declarations regarding the quantity of fuel on board at the time of departure from the private airstrip; these reports stated that between 3 and 4.5 gallons of fuel were in the right tank and that no fuel was in the left tank. However, only 1 gallon of fuel was recovered from the right wing tank, and the left tank was found empty, which was well below the Federal Aviation Regulations (FARs) minimum fuel requirements for flight, which state that "no person may begin a flight under visual flight rules conditions unless there is enough fuel to fly to the first point of intended landing and…to fly after that for at least 30 minutes of flight." Regardless of the pilot's written estimates of the fuel onboard, as noted previously, in his initial statement, he indicated that the airplane only had about enough fuel remaining for 30 minutes of flight, which was still not enough fuel to meet the FARs minimum fuel requirements, and, therefore, his decision to take off at that time was improper. The design of the airplane's wing resulted in both the fuel sight gauge and the dipstick being prone to significantly misrepresenting the actual fuel quantity when the airplane was not level. Therefore, it is possible that the pilot misinterpreted the actual fuel quantity before takeoff. In addition, he exhibited poor decision-making by failing to land earlier in the flight for fuel even though he overflew at least four airports that had fueling facilities. The pilot appeared to have accrued almost 300 hours of flight experience in the airplane since he purchased it about 2 1/2 years earlier. Therefore, he should have had adequate knowledge about its systems and performance capabilities and known that the dipstick and sight gauge were prone to errors and that the airplane would need more fuel to complete the flight. A similar accident in the United Kingdom (UK) resulted in the airplane's UK type certificate holder issuing a service bulletin (SB) that recommended that both sight gauges show fuel in flight and that a landing be performed if any gauge reads empty. The SB also warned that, with one tank empty, the flight can continue provided no turbulence is encountered and the airplane is not flown in a sideslip condition such that fuel moves away from the tank outlet. The airplane's US distributor has not issued an SB regarding flight with one fuel tank empty, and this issue is not addressed in any placards or aircraft operation manuals; therefore, it is possible that the pilot did not realize the limitations of flying the airplane with one fuel tank empty.

Both wings were removed from the airplane, which was then recovered from the accident site, and examined on February 4, 2014, by the NTSB IIC, and representatives from the FAA, Rotax Aircraft Engines, and Flight Design USA. As the state of manufacture, the German Federal Bureau of Aircraft Accident Investigations (BFU) assigned a non-traveling accredited representative. The fuel system was examined and was found to be free of obstructions. Both fuel tanks were intact and did not appear to be breached. The fuel caps were in place, and both cap gaskets were intact and pliable, with the cap vents facing the correct direction. The fuel tanks were inspected internally and no debris, contamination, or de-bonding was observed. Examination of photographs taken at the accident site revealed a circular area of dust surrounding the right wing filler cap, along with a fluid-like streak of dust emanating from the fuel cap and moving aft. Remnants of these signatures were still present during the examination. The photos indicated that the airplane came to rest right-wing-low due to the collapse of the right main landing gear during the impact sequence. The direction of the fuel stain signatures were consistent with a prior tank overfill event, rather than fuel leaking from the tank post-accident. There was no evidence of pre-impact engine malfunction or failure, and following completion of the examination, the engine was started and operated appropriately at various speeds. A complete examination report is contained within the public docket. Fuel System Design The CTSW airplane is equipped with two integral wing tanks, each with a capacity of 17 gallons (16.5 useable). The tanks are 57 inches long by 15 inches wide, extending from the wing root, and positioned forward of the main spar. Fuel quantity is gauged visually within the cabin through a sight-tube located at each wing root rib. Both wings have a dihedral angle of 2 degrees, and a rigid pickup tube with an integral strainer is located at the tank floor at each wing root. Each tank contains a single baffle (anti-sloshing rib) located approximately 21 inches from the root. Fuel passes through the baffle via a series of holes at the leading edge, upper spar cap, and when the fuel quantity is low, through a series of 5 and 8 millimeter holes adjacent to the tank floor. The fuel tanks are vented through vented fuel caps located on the upper outboard surface of the wings. A calibrated dipstick with separate left and right tank increments is utilized to check the fuel quantity when on the ground. Fuel is fed by gravity down two fuel lines in the cabins A-columns; according to the CTSW Maintenance and Inspection Procedures Manual, the lines in the A-columns are of larger volume, "to maintain fuel flow also in sideslip conditions with low fuel for a certain time". The two lines are connected at a T-fitting located on the engine side of the firewall. From the T-fitting, fuel is routed back into the cabin, and through a fuel shutoff valve (on/off only) and fuel filter. The fuel is then routed back through the firewall to the gascolator located adjacent to the lower section of the engine mount, and then onwards to an engine-driven fuel pump. The design allows fuel to be fed from both tanks simultaneously, and there is no provision for the pilot to make a fuel tank selection. Fuel System Testing Both wings were reattached to the fuselage, along with their respective fuel line fittings. The airplane was leveled both laterally and longitudinally and fuel (totaling 3.5 gallons per side), was incrementally added to each tank while simultaneously recording the levels utilizing both the cabin sight gauge, and the Flight Design fuel quantity dipstick found in the airplane. The dipstick quantity generally matched the tank quantity. The sight gauges, although prone to parallax error, were accurate to within 1 gallon. However, it was noted that small changes of the airplane's bank angle resulted in large fluctuations in the quantity observed at the sight gauge; specifically, with 3.5 gallons of fuel in the tanks, lowering the right wing 2 degrees resulted in the indicated fuel dropping to the 1-gallon level. Similar but reversed (due to the location of the cap at the tip of the tank) values were observed at the dipstick for various bank angles. Recovered Fuel Quantity Recovery personnel reported draining about 1.5 gallons from the right wing tank during the recovery, and stated that the left wing tank was empty. They did not observe fuel issue from either of the wing tank fuel lines during removal of the wings from the airframe. When questioned about the method utilized to gauge the recovered fuel quantity, a recovery technician stated that it filled the lower 3 inches of a 5-gallon bucket. The examination group then filled the same bucket with fuel to the 3-inch level and measured the quantity with a calibrated beaker, resulting in an observed total of 1 gallon and 4 ounces (1.03 gallons). Fuel Records Two fueling facilities were located at Coeur d'Alene Airport, and both were capable of supplying 100 low-lead aviation gasoline. Both facilities reviewed their fueling records for the one week period leading up to the accident, and neither could locate records for the pilot or airplane during that period. Whippet Field Airport was a private field comprised of a single turf airstrip. It did not have provisions for refueling. The airstrip was along the presumed route of flight, and about 5.5 miles east of Sisters Eagle Air Airport. The last 170 miles of the route of flight (assuming a heading of 230 degrees magnetic) would have passed within 10 miles of 17 airports, 4 of which had refueling facilities. Pilots Statement Regarding Fuel Quantities The pilot and his attorney provided three separate submissions containing references to the fuel quantity onboard the airplane when it departed Whippet Field Airport. The first included a statement written by the pilot, and signed presumably by a witness reporting that the witness observed the pilot check the fuel quantity utilizing the fuel gauge dipstick, and that the right fuel tank contained 3 gallons of fuel (a separate notation of "over 3 gallons" was written in a different typeface at the end of the sentence). A second document written by the pilot's attorney stated that 4.5 gallons of fuel was present in the right tank. A subsequent email sent by the pilot stated that the airplane was carrying between 3 to 4 gallons of fuel in the right tank. All documents reported that the left tank was empty. CTSW Operating instructions According to the CTSW Airplane Operating Instructions current for the airplane at the time of the accident, the airplane's fuel capacity was 17 US gallons per tank, 16.5 of which is usable. The manual states that fuel is gravity fed, and that the fuel valve has two positions, either "on" or "off". The engine can operate on both 100 low-lead aviation gasoline as well as premium automotive unleaded gasoline which meets American Society for Testing and Materials (ASTM) D 4814 specifications, with a minimum anti knock index of 91. Fuel consumption at takeoff and "75% continuous performance" was 7.1 and 4.9 gallons per hour, respectively. Flight Design discontinued production of the CTSW model in 2007, replacing it with a similar variant, the CTLS. The fuel system remained largely the same with the exception that a return flow flapper valve was included on the fuel tank anti-sloshing rib. Additionally the tanks were interconnected with a vent line, and each tank also vented to its respective wingtip. The CTLS Airplane Operating Instructions, Normal Operating Procedures (Cruise) section, denoted of the following: "Warning: A correct indication on the fuel sight gages in the wing ribs is only possible when the aircraft is leveled. Warning: There is a tendency to fly the CTLS-LSA with a small sideslip ang