WPR25LA070

The pilot reported that, shortly after leveling the airplane at cruise altitude, he felt abnormal vibrations and the engine began running rough. While troubleshooting the anomaly, he adjusted the mixture control, but observed no corresponding effect, and noted that there was no tension on the mixture control cable. The engine subsequently lost total power, and the pilot performed a forced landing to desert terrain. During the landing roll, the landing gear contacted a ditch and the airplane nosed over, resulting in substantial damage. Postaccident examination revealed that the fuel mixture control linkage had separated from the mixture control arm at the rod end bearing. The bolt connecting the rod end bearing to the mixture arm had backed out and was found in the lower cowling. The washers, castellated nut, and cotter pin that secured the rod end bearing to the mixture arm were not recovered during the examination. The mixture arm was observed in the idle-cutoff position during the examination. Review of the airplane’s maintenance logs indicated that the engine controls were checked and lubricated during a condition inspection completed about 10 months before the accident. Another maintenance log entry, dated about two weeks before the accident, detailed several engine maintenance items performed and stated that the engine was inspected in accordance with the scope and detail of 14 Code of Federal Regulations Part 43 Appendix D, which includes the inspection of engine controls for defects, travel, and improper safetying. Whether the maintenance performed at the time of this inspection required detaching the mixture control arm was not determined; however, the attachment hardware should have been inspected for security and proper safetying even if the maintenance performed did not involve the mixture control arm. During the accident flight, the hardware securing the mixture control rod end bearing to the fuel servo control arm likely disconnected and allowed the arm to move to the idle-cutoff position, which resulted in a total loss of engine power.

On December 22, 2024, about 1639 mountain standard time, an experimental amateur-built Vans RV-7A airplane, N1FB, was substantially damaged when it was involved in an accident near Gila Bend, Arizona. The pilot sustained minor injuries, and the passenger was not injured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 personal flight. According to the pilot, after departing Phoenix Goodyear Airport (GYR), Phoenix, Arizona, he climbed the airplane to 2,000 ft above mean sea level (msl). After clearing the Class B airspace shelf, he proceeded to climb to the planned cruise altitude of 4,500 ft msl. About 4,000 ft msl, he adjusted the fuel mixture and engaged the autopilot. About four minutes later, he felt abnormal vibrations from the engine. He began to troubleshoot, but the engine continued to run rough and lose power. The pilot stated that manipulation of the mixture control had no corresponding effect, and that he noticed a lack of tension on the mixture control cable. He moved the throttle control from full throttle to about halfway toward idle, and the engine roughness slightly subsided, but the engine rpm decreased and the engine lost total power. The pilot turned the airplane toward the nearest airport, but realized the airplane would not reach the runway, and he performed a forced landing to a field with tall desert vegetation. During the landing roll, the airplane’s landing gear contacted a ditch and the airplane nosed over, resulting in substantial damage to the left wing. Postaccident examination of the fuel system revealed the bolt that connected the mixture control cable to the mixture control arm had backed out. The missing bolt was recovered from the lower cowling in a pile of brush consistent with vegetation observed at the accident site. The bolt showed no deformation signatures, and the adjoining washers, castellated nut, and cotter pin were not recovered. The bolt that secured the rod end bearing to the mixture bellcrank and its associated hardware was present and unremarkable. The mixture control arm was found in the idle-cutoff position. The throttle linkage attachment bolts, washers, castellated nuts, and cotter pins were present and unremarkable. Review of the airplane’s engine logbook indicated that the engine controls were checked and lubricated during a condition inspection dated February 7, 2024. An entry dated December 2, 2024, stated that the engine crankshaft seal was cleaned and reinstalled due to oil leaks, a magneto was replaced and magneto timing checked, engine oil and oil filter were changed, and new crankshaft propeller flange bushings were installed. The entry stated that the engine was inspected in accordance with the scope and detail of Part 43 Appendix D. Whether any of this work required disconnecting the mixture control cable/arm was not determined. 14 CFR Part 43 Appendix D details items to be included in annual and 100-hour inspections. The components listed forinspection of the engine includes, “Engine controls – for defects, improper travel, and improper safetying.”