Northwest Airlines Flight 421 was a domestic scheduled passenger flight from Chicago, Illinois to Minneapolis, Minnesota that crashed on 29 August 1948. The Martin 2-0-2 aircraft, operated by Northwest Airlines, suffered structural failure in its left wing and crashed approximately 4.1 miles (6.6 km) northwest of Winona, Minnesota, approximately 95 miles (153 km) southeast of Minneapolis. A Civil Aeronautics Board investigation determined that the crash was caused by fatigue cracks in the wings of the aircraft, and recommended lower speeds and frequent inspections of all Martin 2-0-2 aircraft. All 33 passengers and four crewmembers on board were killed. The crash was the first loss of a Martin 2-0-2, and remains the worst accident involving a Martin 2-0-2.