The Korean Air Cargo Flight 8509 crashed near Great Hallingbury, UK shortly after takeoff from London Stansted Airport on December 22, 1999, killing all 4 crew members. An investigation found that one of the aircraft's Inertial Navigation Units had failed, providing incorrect roll data to the captain's attitude indicator. During climbout after takeoff, the comparator warning sounded multiple times due to differences between the captain and first officer's indicators, but the pilots did not respond appropriately despite prompts from the flight engineer. The aircraft entered a steep and uncommanded left bank, crashing 55 seconds after takeoff. Contributing factors included a misdirected repair attempt of the attitude indicator that did not resolve the underlying issue, as well