Flight chaos affecting hundreds of thousands was caused in ‘millisecond’ by software error

UK ministers say report into incident leaves questions unanswered over why problem was not discovered and fixed earlier

A software defect in part of the UK’s air traffic control system corrupted flight data “in the space of a millisecond”, leading to a six-hour outage and mass airline cancellations and delays across the UK last week, National Air Traffic Services has said.

But ministers said that the report into the incident still left questions unanswered, saying they needed “to urgently understand why this issue was not discovered and fixed before it caused chaos”.