He appears in the magazine for the first time in January 1919 where he is noted as Challen, R P, 3rd A[ir] M[echanic], RAF. This information is repeated monthly up to and including the final published roll call in July 1919.
Percy's surviving papers in AIR 79 note his next of kin as his mother, Mrs Clara Margaretta Challen of the Five Bells, Chailey, Sussex. This address was subsequently scored through and replaced with 34 Hartington Terrace, Brighton. He joined the RAF in May 1918 and served in France from 11th October 1918 until 16th February 1919.