N102HAFlight Design Gmbh CTSW · 2007

On September 1, 2013, about 1800 Pacific daylight time, a Flight Design CTSW, N102HA, lost engine power and landed about 1/2 mile short of its intended destination, Sisters Eagle Air Airport, Sisters, Oregon. The light sport airplane was registered to, and operated by, the pilot under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The airplane sustained substantial damage during the accident sequence, and the sport pilot was not injured. The personal flight departed Whippet Field Airport, Sisters, at an unknown time. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot provided a verbal statement to a deputy of the Deschutes County Sheriff's Office following the accident. He reported that earlier in the day he departed from Coeur d'Alene, Idaho, en route to Sacramento, California, and that he encountered strong headwinds and low clouds during the flight. Subsequently he landed at Whippet Field, a private dirt airstrip approximately 5 miles east of Sisters Eagle Air Airport to check the airplane's fuel levels. Estimating that he had sufficient fuel for approximately 30 more minutes of flight, he departed. As he approached Sisters Eagle Airport the engine "sputtered" and then stopped producing power. He stated that the engine then started again, but then stopped. The airplane then struck soft dirt, and according to the pilot, it did not crash, but encountered an, "Off runway landing." He stated that the airplane did not have any mechanical problems, and that it ran out of fuel. He further reported that he was renting the airplane, that it was owned by "World Adventure Series," and that the purpose of the flight was to transport a dog to its new owner in California. In a subsequent correspondence with the NTSB investigator-in-charge (IIC) he listed himself as the airplane's owner.

Subsequent examination revealed that the airplane had sustained substantial damage to the firewall, forward cabin structure, and lower right fuselage.

The pilot did not submit a Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1), or respond to multiple requests from the IIC for a phone interview.

In a subsequent correspondence, the pilot's attorney stated that during the flight the pilot encountered strong westerly headwinds, and was having trouble with bright sun in his eyes, and as a result he experienced difficulty reading the instruments, especially the fuel gauge.

The NTSB IIC requested via email that the pilot answer a series of questions further explaining the accident circumstances. His attorney responded, stating that the pilot had elected to deny the request, asking instead to refer to the circumstances described in the complaint the pilot had filed for damages against Flight Design USA, et al, in the U.S. District Court.

The pilot held a sport pilot certificate; as such he was limited to flying during the hours of daylight. The certificate was issued on November 27, 2011.

The airplane was manufactured in 2007 by Flight Design GmbH, and imported into the United States that year. The pilot purchased the airplane from Flight Design in August 2010, and then transferred ownership to the current owner (a trust located at his home address) in April 2011. According to documentation provided by Flight Design, up until the pilot purchased the airplane in 2010, it had been a demonstration airplane and had accrued a total flight time of about 88 hours. The Hobbs hour meter indicated 382.9 hours at the accident site.

The airplane was powered by a Rotax 912ULS series engine, equipped with a Neuform 2-blade composite propeller. The airplane was equipped with a BRS Aerospace emergency parachute recovery system, which had not been activated during the accident. The most recent documented inspection occurred on November 10, 2012, and was for a condition inspection. At that time, both the airframe and engine had accrued a total flight time of 348.9 hours.

Aviation weather observation stations positioned along the route of flight reported similar weather conditions consisting of clear skies, visibility of 10 miles or greater, and light winds.

The closest National Weather Service weather observation to the accident site was from Roberts Field Airport, Redmond, Oregon, located approximately 17 miles east of the accident site at an elevation of 3,080 feet. The airport had an Automated Surface Observation System, which at 1756 reported wind from 330 degrees at 6 knots, clear skies, and visibility of 10 miles. The next observation at 1856 indicated clear skies but with wind from 310 degrees at 11 knots gusting to 18.

The NWS had no advisories current for the route for any Instrument Flight Rules or mountain obscuration conditions, thunderstorms, icing, or any significant turbulence at the time of any preflight weather briefing prior to departure.

The winds aloft forecast for the region indicated winds at 6,000 feet out of the west-southwest with velocities between 9 and 16 knots. At 9,000 feet, the winds were generally out of the southwest, with velocities of between 12 and 31 knots.

According to the U.S. Naval Observatory, Astronomical Applications Department, the computed sunset occurred in Redmond, at 1940, with civil twilight ending at 2010. At 1810, the sun was 15.6 degrees above the horizon at an azimuth of 265 degrees.

The airplane was manufactured in 2007 by Flight Design GmbH, and imported into the United States that year. The pilot purchased the airplane from Flight Design in August 2010, and then transferred ownership to the current owner (a trust located at his home address) in April 2011. According to documentation provided by Flight Design, up until the pilot purchased the airplane in 2010, it had been a demonstration airplane and had accrued a total flight time of about 88 hours. The Hobbs hour meter indicated 382.9 hours at the accident site.

The airplane was powered by a Rotax 912ULS series engine, equipped with a Neuform 2-blade composite propeller. The airplane was equipped with a BRS Aerospace emergency parachute recovery system, which had not been activated during the accident. The most recent documented inspection occurred on November 10, 2012, and was for a condition inspection. At that time, both the airframe and engine had accrued a total flight time of 348.9 hours.

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 angle. Flight performance is only marginally affected but it can lead to the tanks emptying at different rates. In this case, it is recommended to raise the wing with the fuller tank in a gentle temporarily slip. This can be achieved with the help of the rudder trim, if installed. The aircraft should be returned to level flight after a few minutes and the fuel indication checked. The amount in the tanks should now be more even.

Warning: The tanks in the CTLS have return flow flapper valves on the fuel tank anti-sloshing rib (refer to Chapter 7 Systems Description). They prevent fuel from quickly flowing into the outer tank area during side slipping where it could not be fed into the engine. The return flow valve reduces but does not completely prevent return flow. An exact indication of fuel quantity is thus only possible at the wing root when, after a sideslip, the aircraft has returned to normal flight attitude (and the amount of fuel inside and outside the anti-sloshing rib has evened out)."

The CTSW flight manual did not contain similar verbiage, and neither the CTLS or CTSW manuals, nor any airplane placards or Flight Design USA safety directives made any recommendation regarding flight with one fuel tank empty.

ASTM Standards

The CTSW airplane was designed to comply with the ASTM Consensus Standards, F2245, Revision 4 (Design and Performance of a Light Sport Airplane). The standards make only one reference with regards to unusable fuel:

"7.3.1. The unusable fuel quantity for each tank must be

established by tests and shall not be less than the quantity at which the first evidence of engine fuel starvation occurs under each intended flight operation and maneuver."

By comparison, aircraft certified under 14 CFR Part 23 (Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Category Airplanes) must meet the following standards:

"23.959 (a) Unusable fuel supply. The unusable fuel supply for each tank must be established as not less than that quantity at which the first evidence of malfunctioning occurs under the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank."

CTSW Accident in the United Kingdom

The United Kingdom Department for Transport Air Accidents Investigation Branch (AAIB) investigated an accident on August 12, 2009, involving a similarly equipped CTSW airplane. The airplane experienced a fuel starvation event during the landing approach. It was subsequently determined that at that time, the right tank was empty, and the left tank contained about 1.32 gallons of fuel.

Testing performed during that accident investigation established that with 1.32 gallons of fluid in the right tank, and the wing set to an angle of 8 degrees, the sight gauge indicated that the tank was almost half full. Subsequent tests revealed that with the tank level, it continued to issue fluid at its outlet until only 0.132 gallons remained.

The investigation identified flight planning as a contributory factor and the AAIB issued a recommendation that, "Flight Design GmbH, together with P&M Aviation (the CTSW type certificate holder in the UK), revise their assessment of the unusable fuel in the CTSW aircraft."

P&M Aviation subsequently issued Service Bulletin SB 131. The service bulletin did not make any revisions to the unusable fuel quantity as recommended by the AAIB, but instead recommended a detailed series of actions with regard to monitoring fuel quantities, including the recommendation that both sight gauges must show fuel in flight, and that a landing should be performed if any gauge reads empty. The service bulletin further stated, "if one tank should empty before the other, in level flight the remaining fuel can still be used up....However, if the aircraft is in turbulence and/or the airplane is flown with sideslip putting the outboard end of the feeding tank low, it is possible for the feed to be uncovered and air to be drawn into the system causing the engine to stop."

Fuel Requirements

Federal Aviation Regulation 14 CFR 91.151, under Visual Flight Rules (VFR), "Fuel requirements for flight in VFR conditions" states in part, that no person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed during the day, to fly after that for at least 30 minutes.

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.