Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
prae-vŏlo, āvi, 1, v. n., to fly before or in advance (class.): grues in tergo praevolantium colla et capita reponunt, Cic. N. D. 2, 49, 125: aquila velut dux viae praevolavit, Tac. H. 1, 62 (but the correct read., Plaut. Mil. 1, 1, 41, is praeolat, v. praeolo).