Amateur-built RV-7A N1FB accident near Gila Bend, Arizona

Probable cause

A disconnection of the mixture control linkage during flight, which resulted in fuel starvation and a total loss of engine power. Contributing was the inadequate inspection of the mixture control arm attachment hardware.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for WPR25LA070 for the full record.