N21GX

On April 18, 2023, about 0745 mountain standard time, a Remos Aircraft GMBH Remos GX, airplane, N21GX, was substantially damaged when it was involved in an accident near Glendale, Arizona. The student pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.

The student pilot reported that he was conducting his second solo flight in the accident airplane and had planned to stay in the traffic pattern at the Glendale Municipal Airport (GEU), Glendale, Arizona, for about an hour. He completed two touch-and-go landings and had just lifted off when the engine rpm started to fluctuate. The student pilot adjusted the throttle lever. Despite his efforts, the engine rpm continued to decrease and shortly thereafter the engine and propeller suddenly stopped. The student pilot initiated a forced landing near a road, subsequently impacting terrain.

An onboard camera was located behind the two aircraft seats and was oriented to show a forward-facing field of view that included the instrument panel, partially obscured by the pilot. The video started with the airplane in a shallow base to final turn for the runway at GEU. The pilot maintained frequent hand contact with the throttle lever. After the airplane had landed slightly off the runway centerline, the pilot made several adjustments to undetermined controls and began correcting the airplane back to centerline. The pilot increased the throttle, and the airplane departed the runway. The engine noise became noisier and rougher, and the pilot began more actively manipulating the engine controls. The engine noise reduced in pitch as the pilot continued to manipulate the engine controls. The pilot appeared to cycle the throttle with no apparent change in engine noise. The airplane’s climb began to slow. The engine suddenly stopped, and the pilot turned the airplane to the left and landed hard in a parking lot.

A postaccident examination revealed that the engine remained attached to the engine mounting assembly. Engine cable control continuity was established. Both carburetor throttle linkage springs worked normally. The throttle cable casing end fittings were worn at both carburetor locations. The carburetor heat box door linkage was loose, and the pivot pin was worn. The carburetor heat box control cable was secured to the heat box door linkage with a plastic zip-tie. The magnetic plug was removed from the engine. Small amounts of magnetic material covered the magnetic end of the plug. The reduction gear box was removed, and the interior components appeared to be intact. Wear was observed on the dog hub contact surfaces. Dark oil and sludge were noted on interior components. The reduction gear box was reassembled.

The crankshaft would not rotate by hand. The cylinder rocker covers were removed, and the No. 4 rocker cover had small amounts of metallic fragments on the inside of the cover. The cylinder heads and cylinders were removed from the engine. The cylinder skirts on cylinder Nos. 3 and 4 had mechanical damage. The Nos. 1 and 3 piston heads had impact marks consistent with valve strikes.

The crankcase was examined with a lighted boroscope but images were unable to be captured clearly. Mechanical damage was noted in the No. 4 cylinder bay area. The crankcase was unable to be disassembled due to lack of appropriate tools.

The engine was shipped to the manufacturer and a follow-up examination was conducted. The crankcase was disassembled, and the crankshaft was found separated at the No. 3 connecting rod journal. The separated surface areas were jagged and had metal deformation and thermal discoloration.

The separated surface areas were examined by the National Transportation Safety Board Materials Laboratory. The surface areas revealed a fatigue crack that initiated at the journal surface close to the radius transition to a cheek. The fatigue crack propagated substantially through the thickness of the crankshaft. The terminus of the fatigue crack could not be identified due to contact damage to the fracture face.

The No. 3 connecting rod had impact damage at the crankshaft end. The No. 3 connecting rod bearing had deformation and remained attached to the connecting rod. There was no thermal distress noted with the engine and its components. The remaining bearings (main and connecting rod) showed normal wear conditions. The residual oil found throughout the engine was dark brown in color. The oil filter was disassembled, and its pleats contained metal contaminates consistent with bearing material. A clutch break-away torque inspection was conducted on the reduction gear box. The test resulted in 450 ft-lbs. of torque, which was within the specifications of 441-590 ft-lbs. of torque.

The maintenance records revealed that the total engine time since new was 2,856 hours. This exceeds the manufacturer's recommended TBO, which includes the replacement of the crankshaft. Based on the engine serial number, the TBO was stated as 1,500 hours, with no indication in the maintenance records that it was extended to 2,000 hours.