The traditional approaches are – no surprise – “Big bang” or “Stepwise migration”. To be honest, considering efforts, costs, time and risk, it’s a choice between the devil and the deep blue sea.
Big bang might be an option – most likely the only viable one – for the airport. Big bang needs perfect preparation, everything’s ready, everyone’s trained, flawless timing and orchestration …
Big bang avoids the “in-between” state of two interconnected systems, but it requires high efforts for preparation, paralyzing the entire organization, to counterbalance the high risk of jeopardizing operations.
Stepwise migration creates an “in-between” state with an old integrated system being dismantled, a new integrated system being built up and a link between both that maintains the overall integration. Less risky and less paralyzing due to the step by step approach. But the link needs to be built and adapted along the migration path, requiring its efforts and related costs.