David Beamsley denies six charges of sexual assault as trial opens at Whanganui District Court

David Beamsley is facing six charges of sexual assaulting a female under 12.

A woman says it didn't occur to her to run away from her alleged attacker because she was "too terrified to disobey him".

She was referring to the last of the four times she recalls David Beamsley allegedly sexually assaulting her when she was a child.

Beamsley is on trial at the Whanganui District Court after pleading not guilty to six charges of indecently assaulting a female under 12.

The alleged offending occurred between 1981 and 1984 in South Taranaki and New Plymouth and involved two girls.

"It has stuck in their memory and it is something that has scarred them," Crown prosecutor Chris Wilkinson-Smith told the jury of nine women and three men in opening the trial on Monday.

The first complainant told the court how Beamsley, who is nine years older, would remove her underwear and rub his genital on hers.

"When [he] had decided he had fulfilled his urge he would get up."

She remembered where two of the incidents occurred because the show Chips was on the TV while it happened.

"If I see a re-run of Chips it's a trigger," she said.

"That one is stuck in my mind and I can't shake it."

The witness said Beamsley had told her it was their secret and "if you tell you won't be believed. You'll be the bad person and you'll be taken away from mum and dad and you'll never see them again".

But defence lawyer Debbie Goodlet questioned the witnesses' recollection of the events and suggested it never happened.

"Apart from the sequence of these events and where they occurred you have no memory time-wise or age-wise of when those first two events occurred?

"I suggest that perhaps your memory and recollection are unreliable."

The witness said: "No, they are true and correct."

She also suggested that at the time of the last alleged incident, in a garage, the witness could have run back into her house.

The witness replied: "I could have run away but the thought never occurred to me.

"I knew what was going to happen and I was too terrified to disobey him so I just went in."

The trial before Judge Philip Crayton is expected to last four days.