Northwest Airlines Flight 710

Northwest Airlines Flight 710 was a scheduled flight between Minneapolis, Minnesota and Miami, Florida, with a scheduled stop in Chicago. On March 17, 1960, the six-month-old Lockheed L-188 Electra aircraft serving the flight broke up in the air in southern Indiana, near Cannelton, Indiana, killing the 63 occupants of the plane. After unexpectedly encountering clear-air turbulence at 18,000 feet (5,500 m), the aircraft's right wing and a portion of the left wing broke off the aircraft, causing the fuselage to plummet to the ground and impact the ground at a nearly 90-degree angle, leaving a deep crater. Various parts of the wings landed up to four miles (six point four kilometers) away.

The in-flight breakup of the Electra closely resembled the September 1959 crash of Braniff International Airways Flight 542 which had crashed near Buffalo, Texas, killing the 34 occupants of that aircraft. That flight was also operated with an almost-new Electra. In that crash, the left wing had broken off the aircraft and landed about a mile (2 km) away from the rest of the aircraft. Investigators of that crash had not been able to determine the cause of the breakup, but the similarities between the two crashes led to the Federal Aviation Agency placing flight restrictions on the relatively new Lockheed Electra until a cause could be identified, and ordered Lockheed Corporation to reevaluate the structural integrity of the aircraft and demonstrate its airworthiness. The subsequent investigation, involving over 250 engineers and technicians, discovered that when an Electra with damage to the mounting structures of one of the outboard engines flew at high speeds or in areas of turbulence, a destructive phenomenon called whirl mode wing flutter could occur, leading to wing failure.

After the discovery of the cause of the wing failures, Lockheed launched a program to design the needed structural changes to the aircraft to prevent whirl mode wing flutter from occurring and to apply retroactive modifications to all Electras that were already in service. The changes were successful in resolving the issue, and modifications to the final aircraft were completed on July 5, 1961.