  Three decades ago, heavy-flavor-conserving (HFC) weak decays of heavy baryons
such as $\Xi_Q\to\Lambda_Q\pi$ and $\Omega_Q\to\Xi_Q\pi$ for $Q=c,b$ had been
studied within the framework that incorporates both heavy-quark and chiral
symmetries. It was pointed out that if the heavy quark in the HFC process
behaves as a spectator, then the $P$-wave amplitude of ${\cal B}_{\bar 3}\to
{\cal B}_{\bar 3}+\pi$ with ${\cal B}_{\bar 3}$ being an antitriplet heavy
baryon will vanish in the heavy quark limit. Indeed, this is the case for
$\Xi_b\to\Lambda_b \pi$ decays. For $\Xi_c\to\Lambda_c\pi$ decays, they receive
additional nonspectator contributions arising from the $W$-exchange diagrams
through the $cs\to dc$ transition. Spectator and nonspectator $W$-exchange
contributions to the $S$-wave amplitude of $\Xi_c\to\Lambda_c\pi$ are
destructive, rendering the $S$-wave contribution even smaller. However, the
nonspectator effect on the $P$-wave amplitude was overlooked in all the
previous model calculations until a very recent investigation within the
framework of a constituent quark model in which the parity-conserving pole
terms were found to be dominant in $\Xi_c\to\Lambda_c\pi$ decays. Since the
pion produced in the HFC process is soft, we apply current algebra to study
both $S$- and $P$-wave amplitudes and employ the bag and diquark models to
estimate the matrix elements of four-quark operators. We confirm that
$\Xi_c\to\Lambda_c\pi$ decays are indeed dominated by the parity-conserving
transition induced from nonspectator $W$-exchange and that they receive largest
contributions from the intermediate $\Sigma_c$ pole terms. We also show that
the $S$-wave of $\Omega_b\to \Xi_b \pi$ decays vanishes in the heavy quark
limit, while $\Omega_c\to \Xi_c\pi$ receive additional $W$-exchange
contributions via $cs\to dc$ transition.
