N404NTl Ultralight Sro STINGSPORT · 2005

On January 15, 2021, about 1116 eastern standard time, a TL Ultralight SRO StingSport airplane, N404N, was substantially damaged when it was involved in an accident near Hollywood, Florida. The pilot was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that his preflight inspection and engine run-up revealed no anomalies. During the initial climb from runway 28R, he noted that the airplane’s rate of climb was only 400 feet per minute (fpm); he usually had to try and keep it from exceeding 500 fpm. Shortly thereafter, the engine began to shudder. The pilot transmitted to the tower controller that he had an engine problem and was turning back, and the controller cleared him to land on any runway.

The pilot maneuvered the airplane to land on runway 19R and he believed that, under normal circumstances, he would have had enough runway to complete the landing; however, the airplane’s steep descent angle and speed resulted in a bounced landing, and he stated that the airplane seemed to be gaining speed. He chose to take off again and maneuver the airplane to remain within airport property; however, the airplane did not maintain adequate speed for flight and subsequently impacted a field on airport property. The pilot shut off the fuel and electrical system and egressed the airplane.

Download of data recorded by an onboard GPS unit indicated that the airplane made a right turn just after takeoff and reached a maximum altitude of 308 ft. The airplane then made a descending right turn toward runway 19R, crossing the runway numbers about 182 ft at a groundspeed of 62 knots (kts). With about 1,600 ft of runway remaining, the airplane’s groundspeed was 75 kts.

The next data point showed the airplane at 68 knots with 800 feet of paved surface remaining. The groundspeed at the last data point before the airplane overflew the end of the runway was 57 kts. The remaining data were consistent with the airplane climbing slightly and performing a right turn. Derived groundspeed data showed a decreasing trend. Data ended at 1116:12, with the airplane at rest in an area in the southwest corner of the airport property.

Postaccident examination of the airplane revealed that the carbon fiber, fiberglass, and inner foam core primary structure was substantially damaged. The nose landing gear was pushed back into the firewall and collapsed, and the lower half had separated from the rest of the assembly. The firewall was damaged. The belly of the airplane was torn open by the left main landing gear, which had been forced aft about 24 inches, and sections of the inner foam core had separated from the airplane’s internal structure. Further examination also revealed areas of delamination and cracks in the composite structure.

Examination of the Woodcomp propeller and Rotax 912ULS engine revealed that one blade of the three-bladed propeller was broken off at the hub. The engine did not display any impact damage. After evacuating the oil which had seeped into the No. 2 cylinder when the engine had been stored with the No. 2 cylinder being at the low point of the system, the drivetrain was rotated by hand utilizing the propeller. The propeller speed reduction gearbox and drivetrain rotated freely. During the rotation of the drivetrain, oil was observed to return to the oil tank; there was no evidence of an oil system breach.

Coolant was contained within the coolant system, which remained intact. The right air filter (cylinder Nos. 1/3) was slightly crushed and displayed dirty pleats, and the left air filter (cylinder Nos. 2/4) was in good physical condition, but also displayed dirty pleats. The exhaust system was in good physical condition, but the pipes that connected to the muffler had partially become dislodged during the impact sequence.

Examination of the ignition system revealed no anomalies, and the sparkplugs electrodes appeared to be normal indicating low service hours.

The engine was equipped with two horizontally mounted, float-type, fixed jet, self-leaning carburetors. The right carburetor fueled the right side of the engine (cylinder Nos. 1 and 3), and the left carburetor fueled the left side of the engine (cylinders Nos. 2 and 4).

Examination of the fuel system revealed about 13 gallons of fuel. The fuel system comprised one vented, 20.5-gallon main tank; two vented, 6-gallon auxiliary wing tanks; a shut-off valve; a fuel filter; an electric auxiliary pump with green indicator “ON” light; an engine-driven fuel pump; and the two carburetors. There was also a metered “bleed” return from the fuel pressure line that returned fuel to the main tank.

Further examination of the fuel system revealed that the fuel strainer was full of fuel that was yellow in color and exhibited small rust-colored debris in the bottom of the strainer bowl. both the mechanical and electric fuel pumps were operational.

The float chamber for the right carburetor was also full of fuel that was yellow in color. Debris was seen sitting in the bottom of the float chamber. This debris was large enough to block the main jet and was consistent with material from the fuel line. The combined weight of both floats was 6.4 grams.

The float chamber for the left carburetor was similarly full of fuel that was yellow in color. Debris was also seen sitting in the bottom of the float chamber. This debris was also large enough to block the main jet and was consistent with material from the fuel line. Unlike the right carburetor, one of the floats was found to be sunk in the float chamber and when weighed, the combined weight of both floats was 8.2 grams.

In April 2013, Rotax published a Service Bulletin (SB-912-063) titled: “Replacement of fuel pumps for ROTAX Engine Type 912 (Series).” This service bulletin advised to check the float chamber for any debris particles that could get in during the replacement. If any debris particles should be found, then they must be located. It also advised that if needed, to remove, clean, and install the float chamber. A blog post was also released on the Rotax-Owner website titled: “Rotax 5 Year Rubber Replacement; The Installation Considerations (Part 2)” regarding the 5-year fuel line replacement requirements that talked about the potential of introducing rubber particles into the float bowls from the fuel lines.

Further review of the engine manufacturer’s written guidance revealed that, due to a deviation in the manufacturing process, some floats could absorb more fuel, thus having more weight. This would lead to a loss of float buoyancy and incorrect regulation of the fuel in the float bowl. According to Rotax, possible effects could be a rough-running engine, especially at low speeds; and under some circumstances, a loss of performance and/or fuel leakage in the area of the carburetor.

Page 63 of the Line Maintenance Manual directed that, at 200 hours, the carburetors should be removed for inspection and the weight of the floats should be checked.

Examination of the floats revealed that the floats in the left carburetor exceeded the specified weight of 7 grams. Further examination of the floats also revealed that engine had “B” floats installed, and according to Service Bulletin (SB-912-074) titled: “Exchange of floats (pair) on Rotax Engine Type 912 and 014 (Series)” published on December 3, 2020, the “B” floats should have been replaced with “R” floats.

Review of the maintenance records provided by the pilot, indicated that, on August 27, 2011, the fuel lines on the engine had been replaced with new fuel lines, and the carburetors had been rebuilt. On August 1, 2018, at 301.3 total hours of operation, a 100-, 200-, and 300-hour inspection was completed, along with the 5-year rubber replacement. The last annual condition and 100-hour inspection occurred on December 16, 2020, at 645.2 hours.

Review of data extracted from the installed Grand Rapids Technologies Model 2000 engine monitor indicated that the airplane had only been operated for 3.7 hours since the last annual condition inspection, and no other maintenance entries involving the fuel system were discovered in the owner-supplied maintenance records after that date.

After completion of the examinations, the debris was removed from the carburetor’s float chambers and an engine test run was performed. No anomalies were noted.