What was found
COCKPIT ODOR: AFTER DEPARTURE WE SMELLED A BURNING SMELL THROUGH THE COCKPIT AIR VENTS AND THE PASSENGER AIR VENTS. THE SMELL DISSIPATED AFTER 10 MINUTES OF FLIGHT AND THEN RETURNED ON THE INITIAL PHASE OF THE APPROACH FOR A FEW MINUTES AND THEN DISSIPATED AGAIN . ON THE GROUND WHEN WE PUT THE APU ON WE GET A FAINT SMELL BUT NOT AS STRONG AND IT GOES AWAY PRETTY QUICK. CORRECTIVE ACTION: REPLACED HEPA FILTER. OPS CHECK GOOD. IAW CE-680A AMM 21-70-10.