In my siddur (Shelah, Shaar HaShamayim) it says that tikkun chatzos (specifically tikkun Rachel) is not said on days were tachanun is omitted. On Tisha B'Av we do not say tachanun. However it is hard ...
Why don't we say Avinu Malcanu on Tisha B' Av? The Artscroll Siddur says "on fast days that tachanun is omitted...", is there any other reason?