Question:
Should an avel serve as the shaliach tzibbur and daven for the amud on Tisha B’Av?
Answer:
Yes. The common custom is that an avel does serve as the shaliach tzibbur and davens for the amud on Tisha B’Av. Nevertheless, some authorities disagree and rule that an avel should not daven for the amud on Tisha B’Av, similar to the law on Yom Tov. Practically, the widespread custom is for the avel to daven for the amud on Tisha B’Av.
Regarding the Chabad custom, the accepted practice is that an avel omits davening for the amud only on days when Hallel is recited. Thus, an avel generally serves as shaliach tzibbur on Purim and throughout Chanukah, with the exception of the Hallel prayers. This demonstrates that the determining factor is not necessarily the festive nature of the day, but rather the liturgical status of the prayers.
It should be noted that in 5749, when the Rebbe was in mourning for his wife, the Rebbe served as shaliach tzibbur throughout the year but did not daven for the amud on Tisha B’Av, asking Rabbi Chadakov to do so in his place. However, no proof can be derived from this incident. Aside from the possibility that the Rebbe chose to follow a personal stringency known only to him, there are additional factors that may explain the occurrence. In particular, the Rebbe specifically appointed Rabbi Chadakov to daven in his stead, whereas on days when an avel does not customarily daven for the amud, such as Shabbos and Yom Tov, he simply does not serve as shaliach tzibbur and does not appoint a replacement. This itself indicates that the Rebbe did not necessarily view Tisha B’Av as a day on which an avel should refrain from leading the prayers.
Furthermore, the Rebbe’s mourning was for his wife and not for a parent, and Rabbi Chadakov himself had a yahrzeit for a parent on Tisha B’Av. According to the accepted laws of precedence, Rabbi Chadakov would have held priority for the amud. It is therefore possible that for these or other reasons the Rebbe chose not to lead the prayers on that occasion.
Accordingly, the accepted custom is that an avel does daven for the amud on Tisha B’Av, and no conclusion should be drawn from the above incident to the contrary.
Sources:
Piskei Teshuvos 559:7 (who notes that this is the common custom); Siddur Yaavetz (who rules that an avel should not serve as shaliach tzibbur on Tisha B’Av, similar to Yom Tov); Maaseh Melech p. 236