As Boxtop indicates, the Spanish authorities require 'Advance Passenger Information' for passengers arriving from outside of the Schengen group of countries:
http://www.ryanair.co...n-from-the-uk-ireland
Ryanair used to require passengers travelling to Spain to enter those details online, separately from any other part of their booking and check-in processes. However since ALL Ryanair passengers must now check-in online (where the same information is collected anyway), there's now no separate page to enter those details.
Chris