A Hawaii tour helicopter was not properly maintained when it crashed into waters near Pearl Harbor two years ago, according to a federal report.

The final report from the National Transportation Safety Board indicated that increased inspections by the Federal Aviation Administration may have uncovered the aircraft’s inadequate maintenance and prevented the February 2016 crash, KHON-TV reported Friday.

The pilot and a family of four from Ontario, Canada, were on the helicopter when it went down and sank.

Riley Dobson, 16, died at a hospital four days later from injuries associated with the crash. Two other passengers and the pilot were seriously injured. Another passenger had minor injuries.

A component inside the helicopter’s engine-to-transmission drive shaft did not appear to be properly lubricated, likely causing the assembly to fail from overheating, according to the NTSB report.

NTSB investigators were told that the helicopter underwent maintenance before the crash, but that maintenance was not logged. During that maintenance, grease was not applied as specified in the maintenance manual, according to the report.

Other required maintenance inspections were overdue and were not completed prior to the crash, according to the report.