Cessna 172 N157SF accident near Lincoln, Illinois

Probable cause

The pilot's exceedance of the airplane's critical angle of attack during an aerial survey, which resulted in an aerodynamic stall at an altitude too low to recover.

NTSB analysis

The pilot was conducting an aerial survey flight with two ecologists onboard. Flight track data showed that after departure from the airport, the airplane continued a southwest path toward the destination. According to flight track data, while circling a heavily wooded area near the destination, the airplane entered a right descending turn during which its altitude and groundspeed decreased. The last portion of track data indicated the airplane was traveling to the southwest at an estimated altitude of 1,075 ft mean sea level (msl) and an estimated groundspeed of 50 knots.

A witness reported observing the left wing of the airplane suddenly drop, and another witness reported observing the airplane perform 2.5 rotations while it descended vertically. The airplane impacted a highway and a postimpact fire ensued, which destroyed the airplane.

Postaccident examination of the wreckage revealed no preimpact mechanical malfunctions or failures with the airframe and engine that would have precluded normal operation.

A flight instructor from the operator flew to the accident site shortly after the accident occurred and reported there was “light chop” throughout the flight. A weather model sounding that was created for the accident site near the time of the accident indicated the possibility of light low-level wind shear between the surface and 3,000 ft msl.

Based on the flight track data and witness statements, it is likely the pilot experienced an in-flight loss of control while circling at low altitude near the destination. The pilot likely allowed the airplane’s airspeed to decrease to facilitate the ecologists’ view of the destination site or due to distraction associated with low altitude aerial work. The reduced airspeed and the likely presence of low-level windshear in the area resulted in the pilot exceeding the airplane's critical angle of attack, an aerodynamic stall, and a loss of control at an altitude too low to recover.

Text from the NTSB. Open the NTSB docket for CEN20FA110 for the full record.