https://www.theregister.co.uk/2019/08/02/737_max_cosmic_bit_flipping_test/

Further details have emerged on the 737 Max flight control software bug discovered at the end of June, with reports suggesting that belated tests by a US regulator found the hitherto unknown bug.

The Seattle Times, Boeing's hometown newspaper for many years, explains in detail how timid Federal Aviation Authority regulators eventually woke up and began doing their jobs in full after the two Boeing 737 Max crashes earlier this year.