Patent ID: 8773802

Claim:
A disk drive comprising: a disk comprising a plurality of tracks including a fly height calibration track; a head actuated over the disk; a fly height actuator operable to control a fly height of the head in response to a fly height control signal; and control circuitry operable to: execute a touchdown operation to set an operating fly height control signal by adjusting the fly height control signal until the head contacts the disk; read the fly height calibration track to set a fly height reference; when calibrating the operating fly height control signal, read the fly height calibration track and adjust the operating fly height control signal in response to the fly height reference; determine whether the adjusted operating fly height control signal is valid; and when the adjusted operating fly height control signal is invalid, re-execute the touchdown operation to reset the operating fly height control signal and reread the fly height calibration track to reset the fly height reference.