See http://www.icao.int/publications/Documents/9303_p1_v1_cons_fr.pdf , especially Appendice 8 (p IV-50). The English version is available as http://www.icao.int/publications/Documents/9303_p1_v1_cons_en.pdf , especially Appendix 8 (p IV-47).
I suppose you can't go wrong with what your own passport says :-)
Some obligatory comments: * The -XX variants (Ñ → NXX (N) and Ü → UXX (UE)) can't be intended for human use. * Ŋ → N (shown there with lower-case ŋ – if the implication is that it can't occur word-initially, it's not stated and it's not clear all the other letters can) is surprising. * disallowed: Ä↛A , Ö↛O , Ü↛U (as are: Å↛A , Ø↛O) Stephan
