In this poster, we focus on a new population of high energy radiation events called Flickering Gamma-ray Flashes (FGF) detected during The Airborne Lighting Observatory for FEGS and TGFs (ALOFT) campaign in July 2023 [Ostgaard et al., 2024]. These events do not show evidence of associated detectable optical or radio signals, thereby making their spectral analysis essential for constraining their location and source brightness. We conduct a comprehensive spectral analysis of FGFs using forward modeling and Monte Carlo simulations. This methodology allows us to contrain their source characteristics, including production altitude, radial distance, and source photon brightness (fluence), provided a sufficient number of counts are available. We show that with a few thousand counts, the parameter space (radial distance and altitude) can be constrained to a quadrant. Indeed, the brightest FGF observed during the ALOFT 2023 campaign was about 7000 normal counts. We also show that the contrain could be refined to a kilometer-scale precision if over 50,000 counts were available. Our findings show that all FGFs are consistent with a Relativistic Runaway Electron Avalanche spectrum produced from a given location, that has encountered more or less atmospheric attenuation. They can be produced deep (14 km altitude), and are on average about 1400 to 7000 times less bright than Terrestrial Gamma-ray Flashes (TGFs) detected from space, although their photon brightness can vary by several orders of magnitude.