Narrative:

Winds were calm; sky was clear; and it was just before sunrise. [My student] went to the hangar to preflight the airplane. After approximately 25 minutes of preflight he taxied the airplane to the ramp and shut the aircraft engine off. I walked up and checked the oil; which was five quarts; and checked the fuel visually. I was unable to see down inside the fuel tanks on the C172; but could hear the fuel sloshing around inside. I decided to check the gauges which read 12 on the left tank and four on the right tank. The poh estimates the fuel burn at normal cruise power setting for the C172P as 7.5 gph at 3;000 ft pressure altitude and 2400 RPM. Given this information; I determined that there was [enough] fuel required for our planned lesson of about an hour with more than [enough] reserve required. I estimated the fuel required to be eight gallons and since the fuel gauges read 18 gallons left in the tank; I felt comfortable enough to start the flight. Fuel is available on the airport. I decided that; because we had the fuel to make the flight; we would fuel up after our lesson. We had been in the airport traffic pattern for almost an hour practicing landings and emergency procedures (engine failures) and were nearing the end of our lesson. On the downwind leg for runway xx; at approximately 1;000 ft MSL midfield; our engine lost power. I immediately took control of the aircraft; turned the carburetor heat on; extended flaps; and entered a left base for runway yy. I regained power momentarily after applying carburetor heat; but lost it again. I performed a series of s-turn maneuvers to lose altitude and better position myself to land on runway yy without having to lock the brakes up to keep from running off the runway. I felt I had too much altitude to land on runway yy; but not enough to safely land on runway xx. I touched down about midfield; rolled out to the end of the runway; and exited the runway using the momentum I had left from the rollout. I attempted to start the engine again; which was momentarily successful; but the engine lost power again. I attempted this two more times and was able to taxi half-way down the taxiway before I decided that it really wasn't carburetor ice. I got out and checked the tanks again. As before; I could not really see in them; so I shook the wings and this time I did not hear any fuel sloshing around. The left tank fuel gauge still read 12 gallons and the right tank fuel gauge read empty. As we began fueling the right tank it dawned on me to take a picture of the fuel gauges. I instructed the fueler to fuel only the right tank and he put 15 gallons of fuel in it. I taxied it to ramp where we met my supervisor. The right fuel tank gauge read 12 gallons and the left side read about 14 gallons. He then grabbed a ruler to verify fuel levels. He found only a small amount of fuel in the left tank; which I estimate to be transfer from the 15 gallons we took on the right side. He found the right tank had significantly more fuel than the bit that was in the left tank. The fuel reading was contrary to what was in the left tank.

Google
 

Original NASA ASRS Text

Title: Instructor pilot reported engine power loss due to fuel exhaustion while instructing in the pattern. Pilot noted the fuel gauges were inaccurate.

Narrative: Winds were calm; sky was clear; and it was just before sunrise. [My student] went to the hangar to preflight the airplane. After approximately 25 minutes of preflight he taxied the airplane to the ramp and shut the aircraft engine off. I walked up and checked the oil; which was five quarts; and checked the fuel visually. I was unable to see down inside the fuel tanks on the C172; but could hear the fuel sloshing around inside. I decided to check the gauges which read 12 on the left tank and four on the right tank. The POH estimates the fuel burn at normal cruise power setting for the C172P as 7.5 GPH at 3;000 FT pressure altitude and 2400 RPM. Given this information; I determined that there was [enough] fuel required for our planned lesson of about an hour with more than [enough] reserve required. I estimated the fuel required to be eight gallons and since the fuel gauges read 18 gallons left in the tank; I felt comfortable enough to start the flight. Fuel is available on the airport. I decided that; because we had the fuel to make the flight; we would fuel up after our lesson. We had been in the airport traffic pattern for almost an hour practicing landings and emergency procedures (engine failures) and were nearing the end of our lesson. On the downwind leg for Runway XX; at approximately 1;000 FT MSL midfield; our engine lost power. I immediately took control of the aircraft; turned the carburetor heat on; extended flaps; and entered a left base for Runway YY. I regained power momentarily after applying carburetor heat; but lost it again. I performed a series of S-turn maneuvers to lose altitude and better position myself to land on Runway YY without having to lock the brakes up to keep from running off the runway. I felt I had too much altitude to land on Runway YY; but not enough to safely land on Runway XX. I touched down about midfield; rolled out to the end of the runway; and exited the runway using the momentum I had left from the rollout. I attempted to start the engine again; which was momentarily successful; but the engine lost power again. I attempted this two more times and was able to taxi half-way down the taxiway before I decided that it really wasn't carburetor ice. I got out and checked the tanks again. As before; I could not really see in them; so I shook the wings and this time I did not hear any fuel sloshing around. The left tank fuel gauge still read 12 gallons and the right tank fuel gauge read empty. As we began fueling the right tank it dawned on me to take a picture of the fuel gauges. I instructed the fueler to fuel only the right tank and he put 15 gallons of fuel in it. I taxied it to ramp where we met my Supervisor. The right fuel tank gauge read 12 gallons and the left side read about 14 gallons. He then grabbed a ruler to verify fuel levels. He found only a small amount of fuel in the left tank; which I estimate to be transfer from the 15 gallons we took on the right side. He found the right tank had significantly more fuel than the bit that was in the left tank. The fuel reading was contrary to what was in the left tank.

Data retrieved from NASA's ASRS site as of April 2012 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.