Introduction
An airplane was destroyed following an uncontrolled descent and impact with terrain. The investigation revealed no preimpact anomalies with the airframe, engines, or systems.
Witness Account
A witness reported hearing sounds consistent with stall and recovery procedures, including power reductions and additions. The witness observed the airplane executing a stair step-like maneuver, with the last step occurring at an estimated altitude of 150 to 200 yards above ground level. During this final step, the airplane was in a flat attitude. The witness then saw the airplane enter a counter clockwise spin with a nose down attitude, and no sounds were heard during the spiral.
The instructor pilot had accumulated 5.2 hours of dual instruction since obtaining his multi-engine flight instructor certificate.
Post-Impact Examination
On-scene investigation revealed that the landing gear selector was in the down position and the landing gear actuator was extended. The flap actuator was found extended to 15 degrees. Control continuity was established to all flight control surfaces and both engines.
Engine and Propeller Findings
A thumb compression test at all cylinders of both engines was positive, and all magnetos produced spark. The removed spark plugs were gray in color with a carbon colored coating. Both propellers exhibited an aft bend on one of their blades, as well as chordwise abrasion. All four fuel tanks were found compromised.
No preimpact anomalies were identified in the airframe, engines, or systems.