The National Transportation Safety Board expects to release next week a probable cause for a 2011 Molokai helicopter crash that killed all five people aboard.
The pilot, a Canadian couple and newlyweds from Pittsburgh died when the sightseeing helicopter crashed sideways into mountains above an elementary school.
NTSB spokesman Peter Knudson says a probable cause release date is targeted for next Friday.
The agency released a factual report last week, indicating the investigation is in the final stages.
The factual report says the engine was disassembled and examined, revealing no evidence of any mechanical malfunctions or failures.
Investigators have focused on the tail section.
The report says the helicopter's manufacturer told investigators about four other accidents where the tail rotor separated from the tail boom.