Sequence of events (in English):• 4 April 1979 – TWA Flight 841, a Boeing 727-31 (N840TW), was cruising at 39 000 ft over Saginaw, Michigan, en-route from New York-JFK to Minneapolis.• At 20:55 EST the aircraft suddenly rolled sharply to the right and entered an uncontrolled spiral dive.• Within about 63 seconds the jet lost roughly 34 000 ft, reaching peak speeds of Mach 0.96 and up to 6 g.• The crew managed to regain control at about 5 000 ft after deploying the landing-gear to act as an air-brake and reduce speed.• They diverted to Detroit-Metropolitan Airport and executed a successful emergency landing with no fatalities; all 82 passengers and 7 crew survived, although eight passengers sustained serious injuries.Outcome:The NTSB determined that improper maintenance had allowed the #7 leading-edge slat to deploy asymmetrically during cruise. A critical “flap/slat asymmetry brake” had been deliberately removed and not re-installed during a prior inspection, violating Boeing’s maintenance instructions. This caused the slat to extend, upsetting the aerodynamics and triggering the dive. The incident led to revised maintenance procedures and additional safety checks on Boeing 727 high-lift systems.Root cause (in English):During routine maintenance, mechanics deliberately removed the “flap/slat asymmetry brake”—a component Boeing explicitly prohibits from being taken off—in order to make repetitive tests easier. They then failed to reinstall it. Without this safeguard, the #7 leading-edge slat extended unilaterally in cruise when a hydraulic fluctuation occurred. The resulting asymmetric lift caused the aircraft to roll violently and enter a high-speed dive.