The hypothetical photonic origin of the most energetic air shower detected by the Fly's Eye experiment is discussed. The method used for the analysis is based on Monte Carlo simulations including the effect of precascading of ultra-high energy (UHE) photons in the geomagnetic field. The application of this method to data expected from the Pierre Auger Observatory is discussed. The importance of complementing the southern Auger location by a northern site for UHE photon identification is pointed out.

PACS numbers: 13.85.Tp, 96.40.-z, 96.40.De, 96.40.Pq