CESSNA 152 — Spring, TX

What happened

The purpose of the night instructional flight was to in remain in the airport traffic pattern and practice touch-and-go landings. According to air traffic control data, during the initial climb following the second touch-and-go landing, the flight instructor told the tower controller that the airplane was experiencing "engine problems" and requested to make an immediate 180-degree turn back to the airport for landing. Based on available radar data, the airplane was likely less than 250 ft above the ground when the flight instructor reported the engine problem. A witness reported that, while the airplane was on the downwind leg for the first landing, the engine sounded abnormal and that the engine continued to run roughly while the airplane was on initial climb following the second landing. Several witnesses reported seeing the airplane in a steep left turn before it entered a near-vertical descent into terrain.

A postaccident airframe examination did not reveal any malfunctions or failures that would have precluded normal operation. The carburetor heat control was found in the "off" position. Control cable continuity was confirmed between the carburetor heat box and the cockpit control; however, impact damage to the carburetor air box precluded a determination of whether the carburetor heat was activated at the time of the accident. Although the weather conditions at the time of the accident were conducive to the formation of carburetor ice at reduced engine power settings, the investigation was unable to determine to what extent carburetor ice might have formed during the accident flight.

Additionally, disassembly of the carburetor revealed that one of its two hollow polymer floats was flooded with fuel, which would reduce the buoyancy of the float and could result in poor idle power performance and/or possible flooding of the carburetor. During the 5 years preceding the accident, the carburetor manufacturer issued multiple service bulletins (SB) that acknowledged that the hollow polymer float design had known issues with fuel leaking into the float through a welded seam. The carburetor manufacturer specified that all affected carburetors should be inspected within 30 days and then at 30-day intervals until the affected floats were replaced with an updated solid-epoxy float design that was impervious to flooding. Owner/operator compliance with the service bulletins was considered optional under FAA regulations. According to maintenance documentation, the accident carburetor had not been inspected as specified by the SBs.

Ultimately, the root cause for the partial loss of engine power could not be identified because the investigation was unable to determine to what extent carburetor icing, the flooded float, or a combination of the two conditions could have contributed to the loss of engine power. Following the partial loss of engine power, it is likely that the flight instructor failed to maintain airspeed during the turn back to the airport, which resulted in an aerodynamic stall.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.