Event Summary
While level after descending, the right engine quit. The pilot feathered the propeller and advised air traffic control. The aircraft was being diverted to an alternate airport when the left engine also quit. The pilot positioned the left engine boost pump to high and low, with negative results, but did not feather the propeller. The position of the boost pumps when the engines quit was not determined. The aircraft subsequently landed on an overpass that was under construction. Fuel leakage occurred after the accident due to aircraft damage. The fuel quantity was sufficient.
Investigation Findings
Examination of the aircraft revealed that a flexible duct from the turbocharger to the plenum chamber in the right engine had separated due to a loose clamp. The hose was installed, and a club propeller was installed for each engine run. Both engines operated normally. During the right engine run, the induction air hose was pulled, causing the engine to run rough due to an excessively rich mixture. No determination could be made for the reason of the left engine power loss.
Probable Cause
The probable cause, as stated by the official investigation, was loss of power in the right engine due to a disconnected duct between the turbocharger and the plenum chamber. The reason for the loss of power in the left engine was not determined.