Denial of Petition to Intervene is Appealable The Supreme Court has held that the denial of a petition to intervene in a child custody proceeding is a collateral order that is appealable as of right under Pa.R.A.P. 313. K.C. and V.C. v. L.A., 128 A.3d 774, No. 65 MAP 2015 (Pa. 10/21/2015).