An EA300's center fuel tank quantity gauge indicated approximately half full when empty. The aircraft's engine quit from fuel exhaustion in the landing pattern while feeding fuel from the center tank. An emergency was declared followed by a normal landing.

Narrative

The flight was an instructional flight with the pilot-in-training in the rear seat position. After returning from the training area; the instructor (in the front seat of the Extra 300L) took the controls to demonstrate a formation overhead break approach and over-the-field split-up. Following flight spilt-up overhead the field; the engine began to run rough and then returned to normal operation. The instructor immediately confirmed the pilot-in-training had not touched or done anything in the rear seat. Approximately 15 seconds later; as the aircraft approached the downwind position from the overhead formation split-up; the engine again ran rough. The instructor declared an emergency with Tower; initiated a 180 degree power off approach to the runway and immediately switched the fuel selector to the wing tank position and continued with the power off approach. Approaching short final in the power off approach; there was still no response from the engine. The Instructor switched the fuel selector back to the center tank and landed the aircraft uneventfully. The engine quit on the landing roll out. Inspection of the aircraft revealed an empty center tank and faulty fuel gauge indicator on the center tank. When empty; the gauge indicated approximately half full. The wing tanks had a total of 19 gallons remain at landing. It is likely the engine did not restart when the instructor selected the wing tank position during the 180 degree power off approach due to a sustained side slip to get the aircraft on the final approach profile to land on the mid-point of the center runway. Actions: The center tank gauge was recalibrated and flight tested serviceable. Additional flight tests were completed to determine neither the wing tanks nor the center tank leaked in flight.