The investigation discovered that during maintenance, in order to replace the right outboard flap, the spoilers had been placed in maintenance mode and moved using an incomplete procedure. Specifically, the collars and flags were not fitted. The engineers did not fully understand the purpose of the collars and the way the spoilers functioned. This misunderstanding was due, in part, to familiarity of the engineers with other aircraft - mainly 757 - and contributed to a lack of adequate briefing on the status of the spoilers during the shift handover. The locked spoiler was not detected during standard pilot functional checks.