On 18 December 2017, an A320 crew found that only one thrust reverser deployed when the reversers were selected shortly after touchdown but were able to retain directional control. The Investigation found that the aircraft had been released to service in Adelaide with the affected engine reverser lockout pin in place. This error was found to have occurred in a context of multiple failures to follow required procedures during the line maintenance intervention involved for which no mitigating factors of any significance could be identified. A corrective action after a previous similar event at the same maintenance facility was also found not to have been fully implemented.