Mooney M20J N9133Z accident near Petaluma, California

Probable cause

The pilot's failure to maintain adequate airspeed while departing in instrument meteorological conditions, moderate turbulence, and low-level wind shear, which resulted in the airplane exceeding its critical angle of attack and a subsequent aerodynamic stall.

NTSB analysis

The pilot was departing the non-tower-controlled airport on an instrument flight rules (IFR) flight plan. He received his IFR clearance before departure but the pilot never contacted air traffic control after takeoff. The wreckage was located about 4 hours later about 1 mile from the departure airport. A witness located at the departure airport watched the airplane depart and climb to about 300 ft above ground level (agl) before it initiated a shallow left turn and disappeared into the fog. The witness reported that there were no unusual sounds from the airplane during the takeoff, and that the engine sounded normal.

Instrument meteorological conditions (IMC) were present in the vicinity of the accident site at the time of the accident. In addition, AIRMETs were valid that warned of IFR conditions due to precipitation and mist and moderate turbulence below 10,000 ft. A possibility of light low-level wind shear (LLWS) was identified between the surface and 100 ft agl at the accident site. Multiple pilot reports in the area indicated cloud ceilings around 400-700 ft agl with moderate turbulence. However, the pilot obtained weather information about 6 hours before takeoff, which only included the AIRMETs and not the PIREPs indicated the cloud ceiling and turbulence.

A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The damage to the airplane indicated that it impacted the ground in a nose-down, near-vertical attitude consistent with an aerodynamic stall. Given the weather information available for the accident site around the time of the accident, the pilot likely encountered IMC with areas of turbulence and LLWS almost immediately after takeoff and did not maintain sufficient airspeed for these conditions, which resulted in an exceedance of the airplane's critical angle of attack and an aerodynamic stall.

Text from the NTSB. Open the NTSB docket for ANC18FA028 for the full record.