Primary finding
Probable cause
The pilot’s exceedance of the airplane’s critical angle of attack, which resulted in an aerodynamic stall during an attempted forced landing at low altitude. Contributing to the accident was the loss of engine power for undetermined reasons.
Investigator assessment
Analysis narrative
The pilot reported that, about 45 minutes after takeoff, the engine began to lose power and he attempted a forced landing to a hayfield. As the airplane descended toward the hayfield, the pilot allowed the airspeed to decrease. The airplane stalled and impacted a cornfield, resulting in substantial damage to the fuselage and both wings. Postaccident examination of the fuel system revealed that the fuel cap was loosely installed, and the sight glass indicated the fuel tank was nearly full. Fuel samples from the gascolator contained an unidentified white particulate, with no water detected. The throttle cable was disconnected at the carburetor; this was likely due to the fuselage separation during impact. Examination of the engine revealed no evidence of pre-impact failures or malfunctions that would have precluded normal operation. Examination of the fuel system revealed only a small amount of fuel in the carburetor bowl; however, it could not be determined whether that resulted from impact or an in-flight lack of fuel delivery to the carburetor. Although the FAA’s Carburetor Icing Chart revealed that the reported temperature and dew point conditions were conducive to the formation of carburetor icing at glide and cruise power, the investigation could not determine that the loss of engine power resulted from the formation of carburetor icing.
Source record
Factual narrative
On August 20, 2023, about 0800 central daylight time, a Pietenpol Aircamper airplane, N929DH, was substantially damaged when it was involved in an accident near Hanover, Illinois. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that the morning of the flight he had fueled the airplane with nonethanol MOGAS (automotive gasoline) to a full capacity of 11 gallons and departed Monticello Regional Airport (MXO), Monticello, Iowa, destined for Poplar Grove Airport (C77), Poplar Grove, Illinois. After about 45 minutes of flight, the engine began to lose power. He attempted a forced landing to a hayfield, but the airplane impacted terrain in a cornfield short of the intended forced landing location. The airplane sustained substantial damage to both wings and the fuselage. Postaccident examination of the fuel system revealed that the fuel cap was loosely installed, and the sight glass indicated that the fuel tank was nearly full. The fuel shutoff valve was found in the OFF position; the pilot reported that he had shut the fuel off after the forced landing. Fuel samples from the gascolator contained unidentified white particulate with no water detected. The carburetor bowl contained a small amount of fuel, and about 3 ounces of fuel was observed in the intake pipe after carburetor removal. The carburetor was disassembled and found to be unremarkable, other than slight corrosion noted on the gas adjustment valve needle. The airplane’s modified Ford Model A engine was intact, and the throttle cable was disconnected at the carburetor with the cable pinch bolt still located in the throttle arm. Thumb compression was obtained on all four cylinders, the spark plugs were unremarkable, and a test of the top magneto produced spark on all leads. Postaccident examination of the engine revealed no mechanical malfunctions or failures that would have precluded normal operation. The carburetor icing probability chart from FAA Special Airworthiness Information Bulletin CE-09-35, Carburetor Icing Prevention, supported a potential for carburetor icing at glide and cruise power at the temperature and dew point reported at the time of the accident.