Off the top of my head, two bus routes serve the Croydon Airport Visitor Centre, these being routes 289 operated by Arriva London and 119 operated by Metrobus. As correctly pointed out by Tuck1940, the nearest railway station is Waddon from where a short walk to the Purley Way will enable you to link up the a southbound 289… Route 119 can be picked up from East Croydon train station as there is a bus terminus right outside the station. The 119 terminates at Croydon Airport itself. The 289 can be picked up from either Purley station or near to West Croydon station… It would be handy to know from where you would be traveling as this would enable me to suggest the best method of getting there…

Hope this helps,