Kolb Mark III N18EX accident near Richland, Washington

Probable cause

The pilot's failure to maintain an adequate airspeed above stall speed while executing a steeply banked turn in the traffic pattern.

NTSB analysis

Soon after taking off from the paved runway, the pilot of the experimental airplane leveled off about 200 feet above ground level. At that altitude, and long before reaching the departure end of the runway, the pilot began a 180 degree turn that would bring him onto a low-level downwind where he would soon turn base from this very abbreviated traffic pattern. During the turn, the bank angle of the airplane became very steep, and the pilot failed to maintain an airspeed above the increased stalling speed (Vs) in the steep turn. The airplane stalled and descended at a steep angle into the terrain. Examination of the airplane did not reveal any evidence of a structural or flight control malfunction, and there were no anomalies found with the engine. Witnesses at the airport familiar with the pilot and the airplane stated that the pilot flew this abbreviated low altitude traffic pattern often.

Text from the NTSB. Open the NTSB docket for SEA08LA178 for the full record.