Event Description
A flight instructor and a student pilot were conducting a cross-country flight. They obtained an instrument departure clearance and climbed to VFR-on-top conditions. After reaching VFR on top, the engine rpm decreased to about 1,800 and then further to 1,500. The instructor made unsuccessful attempts to restore power. He then descended through a stratus cloud deck and became visual flight rules (VFR) at approximately 700 to 800 feet above mean sea level. With insufficient power to reach the intended airport, the instructor landed in an open field.
Post‑Flight Examination
Following the landing, examination of the carburetor revealed a fibrous material inside the throat. This material was similar to the lining found inside the intake duct. The duct showed evidence of a prior carburetor fire, which had caused deterioration of the duct lining.
Maintenance Background
The aircraft was a rental unit. Its last maintenance inspection had been conducted 50 flight hours prior to the event.