United Airlines Flight 553

United Airlines Flight 553 was a scheduled passenger flight from Denver to Chicago on December 8, 1972. As it was landing at Chicago Midway Airport, the Boeing 737 aircraft crashed into a residential area, killing 43 of the 61 people onboard and four people on the ground. The crash was primarily caused by the pilots' improper handling of a flap failure and a confusing cockpit situation, combined with unclear communication and an uncontrolled descent. The accident highlighted issues with aircraft design and pilot training, leading to improvements in aviation safety and cockpit procedures.