Brunei's defence ministry has attributed the July crash of an air force Bell 212, which killed 12 and injured two, to unauthorised low-level flying.
The crash occurred on 20 July this year, in clear weather, after 09:17 in the morning, the ministry said in a statement. The aircraft was transporting personnel between two landing zones after the completion of a training exercise.
The aircraft was declared missing at 13:53, upon which search and rescue operations started. Aircraft debris was located at 15:55.
A subsequent board of enquiry attributed the accident to reckless flying.
"The main cause of the [aircraft] crash was human error," the defence ministry said in a statement. "The aircraft was involved in controlled flight into terrain while conducting unauthorised low-level flying."
The pilot was in breach of procedures, and no mechanical issues were found with the helicopter after an investigation by the board and three foreign teams, the defence ministry added.
The pilot was flying at a speed of around 60-80kt (111-148km/h) along a river, banking the aircraft up to 45˚, before the helicopter crashed into a tree.
Following the incident, the board of enquiry recommended that the air force improve training, procedures and safety to prevent the reoccurrence of of such accidents.