NTSB Factual Report

***This report was modified on October 31, 2018. Please see the docket for this accident to view the original report***

On October 15, 2017, about 1000 mountain daylight time, an experimental amateur-built Barber Turbine Cubs PA-18, N181TJ, nosed over during a precautionary landing near Skull Valley, Utah. The private pilot and passenger were not injured. The airplane sustained substantial damage to both wings and empennage. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight that originated from West Jordan, Utah, about 0915.

The pilot reported that prior to departure, he completed a thorough pre-flight inspection. As part of that procedure, he checked the fuel system for water by sumping the fuel tanks, which resulted in no water being found. He stated that the cabin heat was on for the entire flight, due to an outside air temperature of 41° F.

The pilot stated that he completed a low altitude pass at an altitude of about 250 to 300 ft above ground level and applied power to initiate the climb when the engine stumbled slightly and seemed to hesitate. He applied carburetor heat due to concerns about carburetor ice and then subsequently "applied power further to full power." The engine again seemed to hesitate, and the pilot elected to initiate a precautionary landing to an open salt flat area to investigate the problem.

The pilot reported that he conducted a tail low wheel landing and when the airplane touched down, it nosed over and came to rest on its back. The pilot stated that after he exited the airplane, he noted that both main wheel brakes were engaged. He added that neither he nor his passenger applied pressure to the heel brake pedals during the landing sequence.

Review of a photo provided by the pilot's mechanic revealed tire tracks, about 20 to 25 ft in length and consistent with both main landing gear tires, were present on the landing surface.

The airplane was equipped with two brake master cylinders, plumbed to a central reservoir mounted between and above the master cylinders, located beneath the front seat. The master cylinder pedals were connected to the front brake pedals via a rod on each side. The master cylinders are of a design that allowed hydraulic fluid from a separate vented reservoir to gravity feed into the master cylinder or flow back into the hydraulic reservoir to compensate for fluid expansion. An internal check valve that restricts hydraulic fluid movement from the master cylinder to the reservoir actuates if the master cylinder shaft is depressed about 1/16th of an inch.

Examination of recovered wreckage revealed that the left and right brake master cylinders remained secured to their respective mounts. When actuated by hand, the right brake pedal needed minimal input to actuate the brake, however, the left brake pedal needed a significant amount of movement to actuate the brake. Both the left and right main landing gear wheels rotated freely without restriction. The hydraulic reservoir cap was removed, and residual amounts of hydraulic fluid was observed within the reservoir cavity. The vented cap was free of debris and no restrictions were noted. Evidence indicated that the hydraulic fluid drained from the reservoir through the vent following the accident while the airplane was inverted.

The engine and all engine accessories remained secure to their respective mounts. All fuel lines remained attached and secure with no kinks or leaks noted. Throttle, mixture, and carburetor heat control continuity was established from the cockpit controls to the engine. The wooden propeller assembly remained attached to the crankshaft however, one of the propeller blades was separated at the propeller hub. Rotational continuity was established throughout the engine and valve train.

The carburetor was equipped with a carburetor temperature probe. It was noted that one of the two wires were separated from the crimped side of an electrical connector. The wire exhibited missing shielding at the end and no wire was observed within the electrical connector. The carburetor was removed and examined. The throttle and mixture levers moved from stop to stop by hand freely. The accelerator pump functioned normally when the throttle lever was actuated. The carburetor was disassembled, and the internal floats were intact and moved freely. The needle valve and seat were intact.

The airplane was equipped with a Dynon FlightDEK-D180, and when power was applied to the airframe, it functioned, however it was found that the carburetor air inlet temperature display was inoperative.

No evidence of any preexisting mechanical malfunction that would have precluded normal operation of the engine was found. For further information, see the NTSB Airframe Examination Summary in the public docket for this accident.

The Federal Aviation Administration (FAA) published Special Airworthiness Information Bulletin (SAIB) CE-09-35 on June 30, 2009, regarding carburetor ice prevention. The conditions encountered in this accident (ambient temperature 41o F, dew point 23o F) were in the area of icing at glide and cruise power.

NTSB Probable Cause

The activation of the wheel brakes during landing, which resulted in a nose-over. The reason for the wheel brake activation could not be determined.