I believe you are mistaken. Nowhere in ''Humane Vitae'' does the Pope refer to NFP as contraception. The only occurrences of a form of the word "contraception" refer to prohibited techniques. And, "Neither the Church nor her doctrine is inconsistent when she considers it lawful for married people to take advantage of the infertile period but condemns as always unlawful the use of means which directly prevent conception, even when the reasons given for the later practice may appear to be upright and serious. In reality, these two cases are completely different. In the former the married couple rightly use a faculty provided them by nature. In the later they obstruct the natural development of the generative process" (sec. 16). Moreover, it is clear that the US Conference of Catholic Bishops believe that NFP is not a form of contraception. See http://www.usccb.org/issues-and-action/marriage-and-family/natural-family-planning/what-is-nfp/why-nfp-is-not-contraception.cfm/ The same is true of Pope John Paul II who, in his Apostolic Exhortation on marriage, ''Familiaris Consortio'', wrote: "In the light of the experience of many couples and of the data provided by the different human sciences, theological reflectionis able to perceive and is called to study further the difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle: it is a difference whichis much wider and deeper than is usually thought, one which involves in the final analysis two irreconcilable concepts of the human person and of human sexuality."