N72FUCzech Aircraft Works Spol Sro SPORTCRUISER · 2008

On October 15, 2023, about 0759 eastern daylight time (EDT), a Czech Aircraft Works SPOL SRO SportCruiser, N72FU, was substantially damaged when it was involved in an accident in Southport, North Carolina. The student pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The airplane departed from Cape Fear Regional Airport / Howie Franklin Field Airport (SUT), Oak Island, North Carolina.

According to the student pilot, before the flight, he conducted a preflight inspection and did not notice any issues with the airplane. He then started the engine and brought it up to operating temperature, then taxied the airplane from the east ramp via taxiway C to taxiway A and then to runway 5.

He then conducted an engine runup, and all systems checked “green.” He then departed runway 5, and, shortly after takeoff, the engine lost power.

The student pilot then followed the engine out procedures, glided the airplane over the trees at the north end of the runway, and landed it in a vacant lot. During the landing, the left wing struck a palm tree, and the airplane spun around and came to rest.

During a postaccident email exchange and follow up telephone conversation, the student pilot advised that he had “checked” the carburetor heat during the runup before takeoff. When asked where he learned to do this, he advised that his flight instructor had taught him to do it.

Review of manufacturer’s published guidance for the airplane revealed that it did not direct that carburetor heat was to be used before or during takeoff. A note in the emergency procedures section indicated to use carburetor heating during long descents and in areas of possible carburetor icing conditions.

According to FAA records, the pilot held a student pilot certificate. His most recent FAA second-class medical certificate was issued on August 3, 2022. He reported that he had accrued about 101 total flight hours, 23 of which were in the accident airplane make and model.

The accident airplane was a single-engine, two-seat, all-metal, low-wing monoplane of semi monocoque construction and was equipped with a fixed tricycle landing gear with a castering nose wheel. It was designed and built in the Czech Republic, based on the FAA Light Sport category according to American Society for Testing and Materials Standards (ASTM) F2245, F2279 and F2295.

It was powered by a four-stroke, four-cylinder, horizontally opposed, 100 horsepower Rotax 912 ULS2 engine, which featured liquid-cooled cylinder heads, ram-air-cooled cylinders, a dry sump forced lubrication system, a mechanical fuel pump, dual contactless capacitor discharge ignition, and dual carburetors, with one carburetor feeding cylinders Nos. 1 and 3, and the other carburetor feeding cylinders Nos. 2 and 4. The engine’s maximum takeoff rpm was 5,800.

Engine power was controlled by means of the throttle lever and choke lever, which were positioned in the middle channel between the side-by-side seats. (The choke lever is used during cold engine starting procedures.) Both levers were mechanically connected (by cable) to the throttle plates on the carburetors. Springs were also attached to the throttle push rods to ensure that the engine would go to full power if the linkages failed.

The engine was also equipped with carburetor heat, which was controlled by a control lever labeled “CARBURETOR AIR, PULL HOT,” which was installed in the cockpit on the middle panel. When pulled into the on position, the carburetor heat control would allow heated air to be streamed from the heat exchanger to the carburetors through the airbox. (See “Additional Information” for more information about carburetor heat.)

According to FAA and maintenance records, the airplane was manufactured in 2008, and had previously been registered as N173SP. The airplane's most recent annual inspection was completed on July 18, 2023. At the time of the last inspection, the airplane had accumulated 1,302 total hours of flight time.

The accident airplane was a single-engine, two-seat, all-metal, low-wing monoplane of semi monocoque construction and was equipped with a fixed tricycle landing gear with a castering nose wheel. It was designed and built in the Czech Republic, based on the FAA Light Sport category according to American Society for Testing and Materials Standards (ASTM) F2245, F2279 and F2295.

It was powered by a four-stroke, four-cylinder, horizontally opposed, 100 horsepower Rotax 912 ULS2 engine, which featured liquid-cooled cylinder heads, ram-air-cooled cylinders, a dry sump forced lubrication system, a mechanical fuel pump, dual contactless capacitor discharge ignition, and dual carburetors, with one carburetor feeding cylinders Nos. 1 and 3, and the other carburetor feeding cylinders Nos. 2 and 4. The engine’s maximum takeoff rpm was 5,800.

Engine power was controlled by means of the throttle lever and choke lever, which were positioned in the middle channel between the side-by-side seats. (The choke lever is used during cold engine starting procedures.) Both levers were mechanically connected (by cable) to the throttle plates on the carburetors. Springs were also attached to the throttle push rods to ensure that the engine would go to full power if the linkages failed.

The engine was also equipped with carburetor heat, which was controlled by a control lever labeled “CARBURETOR AIR, PULL HOT,” which was installed in the cockpit on the middle panel. When pulled into the on position, the carburetor heat control would allow heated air to be streamed from the heat exchanger to the carburetors through the airbox. (See “Additional Information” for more information about carburetor heat.)

According to FAA and maintenance records, the airplane was manufactured in 2008, and had previously been registered as N173SP. The airplane's most recent annual inspection was completed on July 18, 2023. At the time of the last inspection, the airplane had accumulated 1,302 total hours of flight time.

Airplane

Examination of the airplane revealed that, during the impact sequence with the tree, the left wing with the exception of the wing spar had separated from its mounting location, the fuselage had torn and accordioned back at the left wing root fuselage juncture, and the left landing gear had collapsed and folded back along the left side of the fuselage. The right wing also displayed crush and compression damage along its length, and the right outboard portion was missing the wingtip and was crushed back. The area of the right wing root and fuselage juncture also displayed tearing and crush damage. The fuel strainer (gascolator) screen was clean and free of debris, and the fuel strainer bowl contained a liquid consistent with Mogas (automobile gasoline) with no evidence of water contamination.

Review of photographs revealed that the “CARBURETOR AIR, PULL HOT” control lever was found pulled aft in the on position.

Engine

Examination of the engine revealed all four cylinders’ rocker boxes contained oil, and continuity of the drivetrain was established. Thumb compression and suction were established on all four cylinders. All eight spark plugs (four top and four bottom) were discovered to be heavily carbon fouled, and examination of the interior of the cylinder heads and piston tops revealed that they also were also heavily carbon fouled.

Carburetors

Both the 1/3-cylinder and 2/4-cylinder carburetors were removed for examination and found to be in good condition.

The floats for both carburetors were within acceptable weight limits and showed no signs of fuel absorption. Both float bowls were dry but contained a white powdery residue. (See “Tests and Research” for more information about the residue.)

The main jets were clear of obstructions. The 1/3-cylinder carburetor’s float bracket was properly adjusted with no anomaly observed. The 1/3-cylinder carburetor’s tube assembly for the enrichener (choke) cable was bent, and neither the choke cable nor throttle cable was attached.

The 2/4-cylinder carburetor’s float bracket was bent and out of adjustment. The 2/4-cylinder carburetor’s choke cable was not present, the throttle valve lever was bent toward the carburetor housing, and the throttle cable was fractured near the throttle valve lever attachment.

Spark Plugs

According to maintenance records, the spark plugs were last changed on December 4, 2019, at 1213.1 hrs. The spark plugs installed at that time were NGK DCPR8E, which were the correct type and heat range for this engine. The spark plugs had approximately 88 hours of use prior to the accident flight.

The NGK DCPR8E spark plugs were subject to a 200-hour replacement interval as specified in the Rotax Line Maintenance Manual (LMM). The recorded maintenance entries and hours of use indicated that the spark plugs were within the required replacement timeframe.

Air Filter

The maintenance records indicated that it was a K&N filter, which was cleaned and re-oiled on June 12, 2021, at 1260.2 hrs. The air filter had operated for approximately 41.3 hours prior to the accident flight. The LMM specified that the air filter should be inspected every 100 hours. The recorded maintenance entries and hours of use indicated that the air filter was within the required replacement timeframe.

Carburetor Heat

According to chapter 3 of the FAA’s Aviation Maintenance Technician Handbook – Powerplant (FAA-H-8083-32B), carburetor heat is used to prevent the formation of ice in the carburetor. According to the handbook:

Carburetor icing occurs when the temperature is lowered in the throat of the carburetor and enough moisture is present to freeze and block the flow of air to the engine. The carburetor heat valve admits air from the outside air scoop for normal operation, and it admits warm air from the engine compartment for operation during icing conditions.

The handbook also states the following:

Improper or careless use of carburetor heat can be just as dangerous as the most advanced stage of induction system ice. Increasing the temperature of the air causes it to expand and decrease in density. This action reduces the weight of the charge delivered to the cylinder and causes a noticeable loss in power because of decreased volumetric efficiency. If icing is not present when carburetor heat or induction system anti-icing is applied and the throttle setting does not change, the mixture will become richer. In addition, high intake air temperature may cause detonation and engine failure, especially during takeoff and high-power operation.

The Rotax Heavy Maintenance Manual also provided a warning that stated: “Preheating of the intake air will result in loss of engine performance because of the reduction in air density.”

Rotax Service Bulletin SB-912-079

The activation of carburetor heat and spark plugs (extremely dry, black, and sooty) condition were consistent with the engine running excessively rich during takeoff. Rotax Service Bulletin SB-912-079 included the following points:

Section 3.6.1: Low (cold) air temperature in the airbox is favorable for engine performance. Hot air conditions could be caused by incorrect use of carburetor heat.

Section 3.7.1: Elevated air intake temperatures can contribute to engine issues, particularly when the carburetor heat system is activated along with high engine power settings (during touch-and-go with carburetor heat on).

Section 3.7.1: The misuse of carburetor heat may result in, detonation, loss of power and vibrations.

The airplane was not equipped with a flight recorder, nor was it required to be.

It was equipped with a Dynon Engine Monitoring System (EMS) D120 that recorded various parameters, including manifold pressure, cylinder head temperatures, engine rpm, and fuel system information, as well as airplane position, groundspeed, and ground track information.

The operator had the datalog function enabled, and it was set to record information at 1-second intervals and start recording at boot up. The recording contained data for 11 flights from September 19, 2023, through October 15, 2023. The last recording was identified as the accident flight recording and was about 11 minutes 55 seconds long. The distance from the last recorded sample and the reported wreckage location was about 267 feet.

The highest fuel flow recorded was 8.875 gph, fuel pressure remained above 5.25 psi (minimum allowable is 2.18 psi / 0.15 bar), and the engine rpm showed a gradual, steady degradation.

The electronic device data also indicated the following sequence of events:

- 0751:00 EDT: The device was powered on while the airplane was parked in front of a hangar at SUT.

- 0751:50 – 0755:06 EDT: The airplane taxied via taxiway C, made a left turn onto taxiway A, and held short of runway 5.

- 0757:33 EDT: The airplane turned onto runway 5 and began the takeoff roll.

- 0757:47 EDT: Engine speed reached a maximum of 4852 rpm.

- 0758:01 EDT: Groundspeed was 60 kts.

- 0758:29 EDT: Engine speed reduced to 3237 rpm. Groundspeed was 58 kts.

- 0758:39 EDT: Engine speed was 3267 rpm.

- 0758:40 EDT: Engine speed reduced to 2455 rpm.

- 0758:46 EDT: Engine speed increased to 2967 rpm. Groundspeed was 56 kts.

- 0759:07 EDT: Last recorded data sample. Groundspeed was 50 kts and engine speed was 2656 rpm.

The NTSB materials laboratory examination of both carburetors revealed that the material in the 1/3-cylinder carburetor float chamber was corrosion product from oxidation of the float chamber, which was made of a zinc alloy. The corrosion products had built up on the interior base of the float chamber and around the float chamber jet orifice and readily crumbled when scraped to obtain samples for chemical analysis.