I'm surprised this could happen with only an X8.
GROUND LEVEL RADIATION EVENT
Sunday's powerful X8-class solar flare from departing sunspot AR2673 accelerated a swarm of protons toward Earth, producing a strong solar radiation storm and a "ground level event" (GLE). High-energy particles normally held at bay by Earth's atmosphere and magnetic field penetrated all the way to the ground on Sept. 10th. A leading analyst of GLEs says that radiation dose rates onboard commercial jets flying at high latitudes may have briefly doubled during the episode. Learn more about GLEs and what caused this solar flare to be so effective on today's edition of Spaceweather.com.