Joseph Paul Darcy and Tracy Hope Hartley were due to face the Mandurah Magistrates Court on July 17 but neither appeared.

Both were charged with one count each of attempting to obstruct a security officer in the course of his duties and disorderly behaviour in public.

Darcy also was charged with an additional count of disorderly behaviour in a police station or lockup.

Public Transport Authority prosecutor Garry Gillam told the court the incident happened on a train leaving Warnbro Station at about 8pm on May 9, 2020.

Mr Gillam said the pair engaged in "fellatio" and "sexual intercourse" before they were spoken to by Public Transport Authority officers.

The court heard Darcy became "aggressive" when confronted by the officers and threatened to "knock you two out".

Mr Gillam said Darcy "resisted" but was eventually arrested and transported to Mandurah Transit Station.

Magistrate Vivien Edwards said Hartley faced a maximum total fine of $7000 for her actions.

"The facts of this matter are disgusting to say the least," she said.

Hartley was issued a global fine of $1800 and ordered to pay $225.90 in court costs.

Ms Edwards added that Darcy would need to appear in court for sentencing because he was subject to a suspended imprisonment order at the time of the offence.

An arrest warrant was issued for Darcy and he has since been remanded to appear in court again on August 14.