The iron pnictide (Fe-Pn) superconductors were the second family of high temperature superconductors to be discovered and have a number of different crystal structures. We propose to perform muon spectroscopy (MuSR) measurements on ACa2Fe4As4F2 (A = K, Rb, Cs), which belong to a new family of Fe-Pn high temperature superconductors, with a different crystal structure. We aim to characterize the superconductivity of this family both by probing for broken time reversal symmetry and by determining the superconducting gap structure. MuSR is a powerful technique for determining the superconducting gap symmetry, since the penetration depth can be obtained from probing the internal field distribution. This is important work for the study of iron based superconductivity, since it is currently of great interest whether all Fe-Pn families share a common gap symmetry and pairing mechanism.