/**
  * Return size of warning list
  *
  * @return Number of items in warning list
  */
 AirspaceWarningList::size_type size() const {
   return warnings.size();
 }
 /**
  * Return size of warning list
  *
  * @return Number of items in warning list
  */
 size_t size() const {
   return warnings.size();
 }