When does qiyas (deductive analogy) become bid'ah (innovation)?

From Wikipedia: > In Islamic jurisprudence, qiyas is the process of deductive analogy in which the teachings of the Hadith are compared and contrasted with those of the Qur'an, in order to apply a known injunction (nass) to a new circumstance and create a new injunction. > > In Islam, bid'ah refers to innovation in religious matters. Linguistically the term means "innovation, novelty, heretical doctrine, heresy". The scholars who produce online fatawa seem to use qiyas liberally. Some seem to just go by their gut as to what is true, relying on their past experiences and familiarity with the Qur'an and Sunnah. Particularly in cases when there cannot be precedent in the Qur'an and Sunnah (e.g. software, flights), it's sometimes hard to tell if scholars are simply making stuff up, i.e., bid'ah (instead of saying "I don't know"). **Question**: When does qiyas (deductive analogy) become bid'ah (innovation)? In cases where scholars verge on bid'ah, I feel I should be careful following the instructions. But it's hard to distinguish between what is an inseparable part of Islam and what is a gut feeling of a scholar. Hence this question. There might not be a clear-cut boundary, but some guidelines for identifying bid'ah would be helpful.