NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The flight instructor and the student pilot were practicing touch-and-go landings in the airplane. During the initial climb after the fourth landing, the flight instructor reported an emergency to air traffic control and indicated that he was going to return and land on a runway at the airport. During that transmission, a stall warning horn was sounding. The airplane then spun to the left and descended to impact in a marsh.
The damage to the airplane was consistent with the airplane being in a left spin at impact, and the propeller displayed little damage, which is consistent with the engine not producing power at impact. The fuel selector handle was found positioned to the right main fuel tank; however, examination of the fuel selector's polymeric insert revealed that it had fractured and was in a position that provided openings of about 20% for the right main fuel tank inlet and for the engine outlet, instead of the 100% openings that would have been present with an intact polymeric insert. With only 20% of the normal fuel flow available, the airplane likely experienced a total loss of engine power due to fuel starvation. One of the pilots likely switched fuel tank positions during the previous touch-and-go landing, and the polymeric insert failed at that time. Examination of the wreckage did not reveal any other preimpact mechanical malfunctions.
Metallurgical examination of the fuel selector valve revealed that the lower portion of the polymeric insert exhibited fracture features consistent with rotational ductile overstress. Abrasive wear was present on the outer portion of the insert due to contact with burs on the valve housing. The wear likely took place over a period during which the fuel selector handle would have been difficult to move and excessive force would have been required to move the handle from one position to another.
Review of maintenance records did not reveal any prior anomalies with the fuel selector. The airplane maintenance manual contained instructions, applicable to 100-hour inspections, for the fuel selector to be inspected for condition, security, and operation. The instructions stated that, if the valve binds, sticks, or is otherwise difficult to operate, the fuel selector valve should be lubricated. However, about 5 months had passed since the most recent 100-hour inspection was completed on the airplane. During that time, the airplane had been operated about 78 hours. The investigation could not determine the condition of the fuel selector valve at the last 100-hour inspection.