Cessna U206F N71001 accident near Page, Arizona

Probable cause

The failure of the throttle control cable due to fatigue and maintenance personnel’s failure to replace the cable at the last engine overhaul, which resulted in the pilots’ inability to control engine power and led to a precautionary landing during which the airplane impacted bushes.

NTSB analysis

The commercial pilot, who was the pilot flying, reported that, while he, the copilot, and four passengers were returning to the airport following a sightseeing flight and while the airplane was at 7,500 ft, it would no longer climb. The airplane then slowly started to descend about 350 ft per minute. Unable to stop the descent, the pilots attempted to troubleshoot the problem but were unable to regain engine power. The pilot initiated a precautionary landing onto a dirt road. When the airplane was about 125 ft above ground level, the copilot took control of the airplane and landed it on the road. During the landing roll, the left wing impacted bushes before coming to rest. As the pilots retarded the throttle to idle, the throttle and about 2 ft of the throttle control cable came out of the control panel.

Metallurgical examination of the throttle cable wires revealed flat fracture surfaces that were perpendicular to the wires' axes, and no evidence of necking or other deformation was found, which is consistent with a progressive fracture mechanism, such as fatigue. Therefore, the throttle control cable likely failed due to fatigue and resulted in the pilots' inability to control the engine power.

A review of the airplane's maintenance logbooks revealed that the throttle control cable was installed more than 20 years before the accident. The airplane maintenance manual indicated that the engine controls, including the throttle control cable, should be replaced at every engine overhaul. The operator reported that the last engine overhaul was completed 163 hours before the accident. The logbooks did not indicate that the throttle control cable had been replaced during the overhaul. Given the evidence, maintenance personnel likely failed to replace the throttle control cable at the last engine overhaul, which led to the cable fracturing in flight due to fatigue and the subsequent inability of the pilots to control the engine power.

Text from the NTSB. Open the NTSB docket for WPR17LA144 for the full record.