Deep signal fading due to ionospheric scintillation may cause loss-of-lock on one or more satellites in GNSS receiver tracking loops, which can degrade the navigation availability of GNSS-based aviation applications. Scintillation impact can be mitigated via the frequency diversity, which decreases the chance of satellite loss in the presence of deep and frequent signal fades. This study presents an improved fading process model that generates correlated fading processes of dual-frequency signals and simulates the resulting scintillation impact to evaluate the availability benefit of utilizing dual-frequency GNSS in aviation applications under scintillation. The correlated fading process was described by combining single-frequency only and dual-frequency concurrent fading processes under the assumption that each fading process can be modeled as a Poisson process. Times between deep fading onsets and fading durations observed from GPS L1/L5 dual-frequency measurements collected at Hong Kong in March 2nd, 2014 were used to model the GPS L1 only, L5 only, and L1/L5 concurrent fading processes. Availability simulations for SBAS service supporting the LPV200 phase of flight were conducted by considering the effects of satellite geometry degradation and shortened carrier smoothing time, which are caused by signal losses from deep fades generated by the newly proposed fading process model. A parametric analysis of availability resulting from variations in both the probability of loss-of-lock (under deep fading) and the receiver reacquisition time (following loss-of-lock) was conducted to provide receiver requirement standards for SBAS-based aviation under severe scintillation. The results show noticeable availability improvement from dual-frequency SBAS-based aviation applications over existing single-frequency SBAS.