  Theoretically research of the behavior of $^{41}$K $D_1$ and $D_2$ lines for
$\pi$ polarized resonant light is conducted in the presence of strong magnetic
field when the total electronic angular momentum $J$ and nuclear spin $I$ are
decoupled. We show that in the case of linear polarization and for D1 line
there are two transitions, so called guiding transitions (GT) that maintain
their probabilities and frequency slopes. In Hyperfine Paschen-Back (HPB)
regime other transitions are coming together to those GTs, making 2 groups (4
in each). Each transition in the group has the same frequency slope and
probability as the GT in their group. It is demonstrated that from 12 ($D_1$)
and 20 ($D_2$) initially allowed Zeeman transitions (taking into account the
selection rules) at low B-field, only 8 transitions in each $D$ line remain in
absorption spectra at $B > 200$ G. A complete HPB regime for relatively low
magnetic fields $B \sim 200$ G has been observed. This value is the smallest
for all alkali metals.
