ADSB is a position reporting communication system used by aircraft. The possibility of increasing the global coverage by using a LEO satellite network is studied. As ADSB operates at the same frequency as many other standardised aeronautical applications, it is necessary to estimate whether ADSB messages collisions in orbit will prevent having realtime aircraft position information as required by the GADSS from the ICAO. A simulator was developed to estimate a maximum collision probability of position messages sent from civil aviation aircrafts. Using several assumptions that suggest the worst scenario possible, the simulation was run, and the distribution of several results were averaged. Even in the worst case, the probability to receive a message within one minute is 99.9985%. Those results shown that the reception of ADSB signals onboard satellites is feasible, even in areas with high traffic density, archiving ICAO standards.