Could tiny terrestrial gamma-ray radiation flashes harm airline passengers?

NASA's Fermi Gamma-Ray Space Telescope will join the search for mysterious gamma-ray flashes above thunderstorms, which are ultrabrief but could be hazardous to air travelers. "Just one millisecond blast of the so-called terrestrial gamma-ray flashes (TGFs) could expose passengers and crew aboard a nearby jetliner to the same level of radiation as 400 chest X-rays, according to a recent study."