The jury has retired to consider its verdict in the manslaughter trial of Palmerston North adventure tourism operator Alistair McWhannell.

The 47-year-old is accused of failing to ensure his bridge-swinging operation was safe when Massey University student Catherine Peters, 18, fell about 20 metres to her death at Ballance Bridge, near Woodville, on March 7 last year.

The Crown said he attached Ms Peters to a rope that was too long and not tied to rigging correctly.

Defence lawyer Bruce Squire, QC, said McWhannell was not required to provide a flawless operation.

"He's under a duty to take the care a reasonable man would take in those circumstances," Mr Squire told the court in his final address.

Justice Ronald Young summed up the case before the jury retired late this morning.