C172 pilot reported engine operating at low power resulted in an off airport landing.

Attributes
ACN	1685957
Time
Date	201909
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	Direct
Flight Plan	VFR
Component
Aircraft Component	Engine
Person 1
Function	Pilot Flying
Qualification	Flight Crew Commercial Flight Crew Instrument
Experience	Flight Crew Last 90 Days 1.5 Flight Crew Total 1060 Flight Crew Type 750
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Clearance

Narrative:

I was flying with a cfii doing a bi-annual on a rr (round-robin) between ZZZ and ZZZ1. We departed ZZZ1 flying direct to ZZZ at 1700 foot. Note that we departed ZZZ with 3.5 hours of fuel. Shortly before the midpoint of the return leg the engine suddenly/instantaneously was running rough. The cfii immediately asked for the controls and I granted them. We tried carb heat; switched the mags. The engine continued to run with a max RPM estimated at 1200. Applying throttle would cause the engine to immediately lose RPM and begin windmilling. We were in a rural area with no close airports and the cfii made the correct decision to set the plane down instead of trying to nurse an engine with 1/4 power. We had a few field options; chose one and set down with no issues for the passengers or aircraft.

Original NASA ASRS Text

Title: C172 pilot reported engine operating at low power resulted in an off airport landing.

Narrative: I was flying with a CFII doing a bi-annual on a RR (Round-Robin) between ZZZ and ZZZ1. We departed ZZZ1 flying direct to ZZZ at 1700 foot. Note that we departed ZZZ with 3.5 hours of fuel. Shortly before the midpoint of the return leg the engine suddenly/instantaneously was running rough. The CFII immediately asked for the controls and I granted them. We tried carb heat; switched the mags. The engine continued to run with a max RPM estimated at 1200. Applying throttle would cause the engine to immediately lose RPM and begin windmilling. We were in a rural area with no close airports and the CFII made the correct decision to set the plane down instead of trying to nurse an engine with 1/4 power. We had a few field options; chose one and set down with no issues for the passengers or aircraft.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.