VANCOUVER - A Transportation Safety Board investigation could not find the cause of a deadly helicopter crash in Campbell River, B.C., last October.

There were two pilots on a training run aboard the Robinson R44 Astro helicopter when the chopper went down near the Campbell River airport on Vancouver Island.

The board says its investigation found that shortly after the controls were transferred back to the main pilot, the helicopter began to spin and crashed into some trees.

The pilot in the left seat was killed and the pilot in the right was seriously hurt, but managed to call 911 on his personal cellphone, prompting a search.

A report from the board released Monday says it found evidence of wear on drive belts, and gouges and loose bolts on an engine cooling fan, but wasn't able to determine if either were factors in the crash.

Because there were no data or voice recorders, the board says more information was not available and it has recommended in the past that Transport Canada make such recording systems mandatory for lightweight commercial and private operators.