Accident Circumstances
The aircraft was conducting an ILS approach at dusk in instrument meteorological conditions (IMC) with icing conditions present and the alternate air selected. According to the pilot, shortly after descending below an overcast layer on final approach, the engine lost power and did not respond to throttle inputs. A forced landing was executed in a wooded area short of the runway. The aircraft sustained extensive damage.
Engine Examination
During an examination of the engine, the turbocharger and wastegate transition pipes were found separated at the flange. Carbonaceous residue was observed in the area of separation, but no heat damage was evident. The gasket, bolts, washers, and self-locking nuts used to secure the pipes together were not located. Subsequently, the engine operated successfully during an operational check.
Similar Incidents
The investigation identified three similar cases of pipe separation involving another aircraft type. In those incidents, only partial losses of power were reported.
Environmental Conditions
The right front seat passenger reported seeing a trace of ice on the wings as the aircraft was descending through clouds. The pitot heat, stall warning heat, and ice light switches were found in the 'off' position. At 1650 CST, the surface temperature was 36°F and the dew point was 35°F.
Occupant Injuries
All three occupants sustained serious injuries.