Amateur-built ZODIAC N601LL accident near Stockton, Alabama

Probable cause

A partial loss of engine power due to a missing exhaust clamp bolt and subsequent oil loss due to a damaged engine oil return line, which resulted in the pilot’s decision to perform an off-airport landing.

NTSB analysis

According to the pilot of the experimental amateur-built airplane, on the final leg of a cross-country flight he detected an odor, and as the odor intensified, he also noticed an increase in heat. The pilot decided to divert to the nearest airport and then observed a reduction in engine power and oil droplets on his windscreen. While he searched for a suitable landing site he observed fluctuating oil pressure, followed by an audible oil pressure warning tone. The pilot initiated off-airport landing to a field. The airplane subsequently impacted a fence and sustained substantial damage to the fuselage and both wings.

During a post-accident examination of the engine the turbocharger down pipe exhaust clamp bolt was missing, and the exhaust down pipe had disconnected. Additionally, the turbocharger oil return line exhibited thermal damage and was saturated with engine oil. Given these findings, it is likely that the release of hot exhaust gases prevented the turbocharger’s waste gate from functioning normally and resulted in the partial loss of engine power observed by the pilot. The thermal damage to the oil return line likely resulted in the fluctuating engine oil pressure and subsequent loss of oil.

Text from the NTSB. Open the NTSB docket for ERA26LA348 for the full record.