Agusta A109 N11NM accident near Brainerd, Minnesota

Probable cause

The pilot's spatial disorientation during an instrument approach in dark night instrument meteorological conditions, which resulted in a loss of control and subsequent impact with terrain.

NTSB analysis

The crew of the helicopter air ambulance flight was approaching the airport for landing in dark night instrument meteorological conditions (IMC) after delivering a patient to the hospital. The reported weather conditions about the time the pilot initiated the instrument landing system (ILS) approach included 1/2-mile visibility with haze, which then deteriorated to 1/4 mile, which was within the operator's approved visibility approach minimums. The paramedic onboard reported that he saw the runway environment through a thin layer of fog as the helicopter descended toward the decision height (DH) of 200 ft above ground level during the approach.

After descending below the DH, with a power setting below 30% torque, the helicopter's pitch attitude increased from -3° (nose-down) to +20° (nose-up), its airspeed decreased from 100 to 50 knots, and the pilot declared a missed approach, likely due to a loss of visual contact with the runway environment. The pilot's increased collective input and the helicopter's decreasing airspeed resulted in an increase in torque, and the helicopter entered a right rotational yaw that accelerated into a spin. The helicopter subsequently impacted terrain near the runway.

The dark night conditions at the rural airport resulted in little to no visual references during the pilot's transition to landing and the attempted missed approach. It is likely that the pilot became spatially disoriented, which led to the excessive pitch attitude, slow airspeed, his failure to recognize and arrest the right yaw, and the subsequent loss of control.

Text from the NTSB. Open the NTSB docket for CEN19FA185 for the full record.