THE AIRCRAFT'S LACK OF SINGLE ENGINE PERFORMANCE TO MAINTAIN ALTITUDE AFTER THE ENGINE LOST POWER. FACTORS RELATED TO THE ACCIDENT WERE: DISPLACEMENT/MECHANICAL INTERFERENCE WITHIN THE ACCESSORY DRIVE GEAR SYSTEM OF THE LEFT ENGINE, FAILURE OF THE LEFT ENGINE ACCESSORY DRIVE GEAR SHAFT, AND THE FAA'S INADEQUATE CERTIFICATION/APPROVAL OF THE OPERATOR, IN ORDER TO ASSURE COMPLIANCE WITH 14 CFR 135 CONCERNING THE ENGINE-OUT CAPABILITY.