Accident Overview
On April 18, 2023, about 0745 mountain standard time, a Remos Aircraft GMBH Remos GX, N21GX, was substantially damaged when it impacted terrain 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.
Flight Details
The student pilot was conducting his second solo flight in the accident airplane and planned to stay in the traffic pattern at Glendale Municipal Airport (GEU) for about an hour. He completed two touch-and-go landings. After lifting off, the engine rpm began to fluctuate. The student pilot adjusted the throttle lever, but the rpm continued to decrease, and the engine and propeller suddenly stopped. The pilot initiated a forced landing near a road, and the airplane impacted terrain.
Onboard Video Observations
An onboard camera located behind the seats captured forward-facing video that included the instrument panel, partially obscured by the pilot. The video showed the airplane in a shallow base-to-final turn for the runway. The pilot frequently touched the throttle lever. After landing slightly off the runway centerline, the pilot made several adjustments to undetermined controls and corrected the airplane back to centerline. The pilot increased throttle, and the airplane departed the runway. Engine noise became rougher, and the pilot actively manipulated engine controls. The engine noise reduced in pitch, and the pilot cycled the throttle with no apparent change. The climb slowed, the engine stopped, and the pilot turned left, landing hard in a parking lot.
Postaccident Examination
The engine remained attached to its mounting assembly. Cable control continuity was established. Carburetor throttle linkage springs worked normally, but throttle cable casing end fittings were worn at both carburetor locations. The carburetor heat box door linkage was loose, with a worn pivot pin; the control cable was secured with a plastic zip-tie. The magnetic plug had small amounts of magnetic material. The reduction gear box components appeared intact, with wear on dog hub contact surfaces and dark oil/sludge noted internally. The crankshaft would not rotate by hand. Cylinder rocker covers were removed; the No. 4 cover contained metallic fragments. Cylinder skirts on Nos. 3 and 4 had mechanical damage. Pistons Nos. 1 and 3 had impact marks consistent with valve strikes. A boroscope showed mechanical damage in the No. 4 cylinder bay area, but images were unclear; the crankcase could not be disassembled on site.
Engine Examination
The engine was shipped to the manufacturer, where the crankcase was disassembled. The crankshaft was found separated at the No. 3 connecting rod journal. The separated surfaces were jagged with metal deformation and thermal discoloration. NTSB Materials Laboratory examination revealed a fatigue crack that initiated at the journal surface near the radius transition to a cheek. The fatigue crack propagated substantially through the crankshaft thickness; the terminus could not be identified due to contact damage. The No. 3 connecting rod had impact damage at the crankshaft end; its bearing was deformed but attached. No thermal distress was noted. Other bearings showed normal wear. Residual oil was dark brown. The oil filter contained metal contaminants consistent with bearing material. A clutch break-away torque test on the reduction gear box yielded 450 ft-lbs, within the specified range of 441-590 ft-lbs.
Maintenance Records
Total engine time since new was 2,856 hours, exceeding the manufacturer's recommended time between overhauls (TBO) of 1,500 hours; there was no indication in the records that the TBO had been extended to 2,000 hours.