both havok and dazzler only "flew" once, and both are considered to be flukes. off the top of my head, i don't recall the incident around blaire's, but havok's powers create NO kickback, meaning there's no way for him to direct thrust to propel himself. the writer didn't know that and was trying to be inventive, but wound up creating a largely ignorable scene instead.
the orphan, apparently, can levitate through non-genetic means. he's the only one i can think of off the top of my head.