A position error signal amplitude indicative of the distance between an expected
position of a magnetic head relative to the track centerline of a magnetic data
storage and retrieval system and an actual position of the magnetic head relative
to the track centerline is detected and filtered. The signal is filtered to generate
a sway mode signal amplitude indicative of an oscillation of the actual position
of the magnetic head relative to the track centerline in the frequency range of
the filter. The absolute value of the sway mode signal amplitude is then determined.
If the absolute value of the sway mode signal exceeds a predetermined threshold
value that correlates to a high probability of impending a head-disk crash, a warning
signal is propagated. Alternative embodiments similarly predict the possibility
of head-disk crash on the basis of the maximum value of several samples of the
position error signal and on the basis of the maximum value of several samples
of the square of the position error signal amplitude
