What happened
During a two-hour and 40-minute training mission, the pilot operated the aircraft at a low power setting with the fuel mixture set to full rich. Following the mission, the pilot climbed to 9,000 feet AGL to clear obstacles between the current location and the destination. During the subsequent descent, the pilot reduced power more rapidly than usual, resulting in a descent rate faster than normal at approximately 180 KIAS.
As the aircraft entered the traffic pattern at an altitude of approximately 800 to 1,000 feet AGL, the pilot applied power, at which point both engines lost total power. The pilot established an 85 KIAS glide, completed emergency procedures, and retracted the landing gear. The engines failed to restart. The pilot did not feather the propellers and extended the landing gear prior to touchdown. The pilot stated that he did not flare the aircraft during the landing, which resulted in the aircraft colliding with the ground. There were no injuries reported.
The investigation
An examination of the engines revealed soot on all spark plugs. Despite this finding, both engines started and operated normally from idle to full acceleration during the post-accident examination.
Technical documentation was reviewed, including the engine manual and the Pilot's Operating Handbook (POH). The engine manual contains a note stating that long descents at low power should be avoided because engines may cool excessively and may not accelerate satisfactorily when power is reapplied. Additionally, the POH recommends feathering propellers and maintaining a glide speed of 120 KIAS in the event of a dual engine failure.