dynamic fly height control is obtained for a read / write head by use of a heating element having two laterally separated heat sources symmetrically spaced around the track center line of the head . the two heating sources create a protrusion profile relative to the undistorted abs that recesses the read element and main write pole at the track center line relative to off - track positions . the resulting dfh control also protects the head from hdi events that are either the result of calibration procedures or normal hdd operation .