Narrative:

I had completed my pre-flight checks as usual; including checking the quantity of fuel (full; 38 gallons useable) and sumping the tanks to check for water or sediment (none found). No dripping/leaking appeared from the petcocks on the fuel sumps at that time. The aircraft is a cessna 172 owned by [FBO]; of which I am a member. I have approximately 30 hours in this specific plane; including around ten hours of flight in the preceding week (and nearly five hours the previous day). Planned flight was a sight-seeing trip to ZZZ1 with one passenger. Conditions were VMC throughout the flight; and we were proceeding smoothly. Upon crossing ZZZ2 on my return; I calculated that I should have 45 minutes of fuel remaining when I landed in ZZZ; including double-checking my log to confirm my time in flight. Feeling comfortable with my fuel reserves; I continued towards ZZZ.first indications of trouble came approximately 10 miles east of ZZZ. A light rain was falling; and I turned on carb heat as a precautionary measure (air temperature was in the range for known carb ice possibility). Shortly after; the engine faltered; which I believed to be carb ice melting and burning off. The engine began running more smoothly; and I continued towards ZZZ. I made a radio call to ZZZ tower to relay my location and request clearance to land; thinking the issue had been resolved with the application of carb heat. Shortly after; the engine faltered again; and I began a more comprehensive check. I pitched the plane for maximum glide; ran the plane on each magneto individually (then back to both); engaged the auxiliary fuel pump; checked the position of the primer; cycled the throttle; confirmed mixture on full-rich; checked engine gauges (including fuel gauges; which showed fuel to be appropriately low but not exhausted) and changed the fuel selector from 'both' to each individual tank. The engine began to run again briefly when placed on the left tank; and beginning to suspect fuel starvation; I rocked the wings back and forth attempting to slosh fuel into the lines. Around this time I made a second radio call to the tower advising engine trouble. It became clear at this time that an [off airport] landing was my safest option; and I continued to glide while identifying an appropriate location. I flew over [highway] and parallel to a large field without fences. I planned to land in the field unless the road was clear. A large (approximately one mile) gap was available on the road; and I advised the tower that I would be making an [off airport] landing several miles east of the airport. I was able to land safely and coast to a road; where I pulled the plane off the highway. I advised tower that I was safely on the ground and clear of the roadway. Tower advised that they had called law enforcement about the forced landing. Upon landing; highway patrol and local sheriff arrived to confirm that there were no injuries. Sheriff indicated that there was no crime committed by making a safe forced landing. I also spoke with the management and mechanics of the flight club. Then mechanics asked that I check the plane for any abnormalities while they came to meet me. At this time I sumped the tanks again; finding a small amount of fuel in the left tank. When I checked the right tank; I discovered that the petcock for the sump drain was partially retracted; and found it completely dry. I conferred with the mechanics upon their arrival; compared the fuel burn to logs from previous flights; and recalculated my anticipated fuel burn during my flight. The consensus appears to be that approximately 6 gallons of fuel drained from the petcock while in flight; accounting for the difference between my estimated fuel reserves and actual fuel reserves. The mechanics also suggested that airspeed while aloft may have increased the rate of leakage from the petcock. I believe that this issue was caused by a combination of equipment malfunction and my pre-flight inspection.I could possibly have identified the issue and avoided the problem if I had manually checked the retraction of the fuel sump rather than simply draining and checking for a leak at field elevation. This will certainly be included in all future pre-flight inspections I perform. I take this experience as a stern warning that any component of an inspection may reveal potentially life-threatening issues; and that only with extreme diligence can an inspection be considered sufficient. I also take from this experience the importance of good training; which I believe to be the greatest factor in the safe outcome of today's flight.

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Original NASA ASRS Text

Title: C172 pilot reported a fuel starvation event; possibly due to a malfunctioning petcock; that resulted in a forced landing on a public highway.

Narrative: I had completed my pre-flight checks as usual; including checking the quantity of fuel (full; 38 gallons useable) and sumping the tanks to check for water or sediment (none found). No dripping/leaking appeared from the petcocks on the fuel sumps at that time. The aircraft is a Cessna 172 owned by [FBO]; of which I am a member. I have approximately 30 hours in this specific plane; including around ten hours of flight in the preceding week (and nearly five hours the previous day). Planned flight was a sight-seeing trip to ZZZ1 with one passenger. Conditions were VMC throughout the flight; and we were proceeding smoothly. Upon crossing ZZZ2 on my return; I calculated that I should have 45 minutes of fuel remaining when I landed in ZZZ; including double-checking my log to confirm my time in flight. Feeling comfortable with my fuel reserves; I continued towards ZZZ.First indications of trouble came approximately 10 miles east of ZZZ. A light rain was falling; and I turned on carb heat as a precautionary measure (air temperature was in the range for known carb ice possibility). Shortly after; the engine faltered; which I believed to be carb ice melting and burning off. The engine began running more smoothly; and I continued towards ZZZ. I made a radio call to ZZZ tower to relay my location and request clearance to land; thinking the issue had been resolved with the application of carb heat. Shortly after; the engine faltered again; and I began a more comprehensive check. I pitched the plane for maximum glide; ran the plane on each magneto individually (then back to both); engaged the auxiliary fuel pump; checked the position of the primer; cycled the throttle; confirmed mixture on full-rich; checked engine gauges (including fuel gauges; which showed fuel to be appropriately low but not exhausted) and changed the fuel selector from 'both' to each individual tank. The engine began to run again briefly when placed on the left tank; and beginning to suspect fuel starvation; I rocked the wings back and forth attempting to slosh fuel into the lines. Around this time I made a second radio call to the Tower advising engine trouble. It became clear at this time that an [off airport] landing was my safest option; and I continued to glide while identifying an appropriate location. I flew over [highway] and parallel to a large field without fences. I planned to land in the field unless the road was clear. A large (approximately one mile) gap was available on the road; and I advised the Tower that I would be making an [off airport] landing several miles east of the airport. I was able to land safely and coast to a road; where I pulled the plane off the highway. I advised Tower that I was safely on the ground and clear of the roadway. Tower advised that they had called law enforcement about the forced landing. Upon landing; Highway Patrol and local sheriff arrived to confirm that there were no injuries. Sheriff indicated that there was no crime committed by making a safe forced landing. I also spoke with the management and mechanics of the flight club. Then mechanics asked that I check the plane for any abnormalities while they came to meet me. At this time I sumped the tanks again; finding a small amount of fuel in the left tank. When I checked the right tank; I discovered that the petcock for the sump drain was partially retracted; and found it completely dry. I conferred with the mechanics upon their arrival; compared the fuel burn to logs from previous flights; and recalculated my anticipated fuel burn during my flight. The consensus appears to be that approximately 6 gallons of fuel drained from the petcock while in flight; accounting for the difference between my estimated fuel reserves and actual fuel reserves. The mechanics also suggested that airspeed while aloft may have increased the rate of leakage from the petcock. I believe that this issue was caused by a combination of equipment malfunction and my pre-flight inspection.I could possibly have identified the issue and avoided the problem if I had manually checked the retraction of the fuel sump rather than simply draining and checking for a leak at field elevation. This will CERTAINLY be included in all future pre-flight inspections I perform. I take this experience as a stern warning that any component of an inspection may reveal potentially life-threatening issues; and that only with extreme diligence can an inspection be considered sufficient. I also take from this experience the importance of good training; which I believe to be the greatest factor in the safe outcome of today's flight.

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.