Flight Details
According to the company's chief maintenance inspector, the purpose of the flight was to conduct a maintenance test flight of the airplane on recently installed equipment completed by the pilot/mechanic. Before engine start-up, the pilot/mechanic conducted a pre-flight inspection, then taxied to the ramp and ran the engine up to full rpm three consecutive times prior to the test flight.
The pilot then taxied to runway 32 and applied full power for take-off. As the airplane began to rotate for climb out, the engines sounded like they began to "backfire." The engines continued to make this sound during the climb. The airplane climbed approximately 200 feet, at which point the left wing pitched down. The airplane descended under the tree line, and a "loud explosion" was heard. The airplane collided with a building a quarter mile from the departure end of runway 32.
Post-Accident Examination
A post-accident examination of the cabin section, main fuselage, and wing assemblies revealed that they were fire damaged. All flight control and communication instruments were also fire damaged. Examination of blades from both propeller assemblies revealed rotational scoring, and both propellers were rotating and not in the feathered position. No pre-impact mechanical anomalies were noted with the propeller blades.
Review of the maintenance work order revealed that a Shadin Digilfo-L fuel flow indicator and fuel flow transducers on the right and left engines had been installed by the pilot/mechanic prior to the flight. The left fuel flow transducer (serial number 130436) was found charred, and its inlet hose coupler was not as tight as the outlet hose coupler. When fuel was poured into the inlet side of the transducer, the outlet flow was restricted. The fitting on the inlet side was removed, and inspection revealed debris around the inlet orifice. After removal of the debris, fuel poured into the inlet and exited without restriction.
The right fuel flow transducer (serial number 130437) was intact with no visible damage, and both hose couplers were tight. Fuel poured into the inlet side exited the outlet side without visible restriction to flow.