What happened
On the afternoon of the accident, a L-188A Electra, registered as N9707C, departed from Houston Hobby Airport (HOU) bound for Dallas Love Field (DAL). After climbing to 20,000 feet, the flight crew encountered intense thunderstorm activity. In an effort to navigate around the weather, the crew requested a descent and a westward deviation. Despite warnings from air traffic control regarding other aircraft moving east to avoid the cells, the crew proceeded with a westward course.
As the flight progressed, the aircraft was cleared to descend through various altitudes, eventually reaching 5,000 feet. At approximately 16:47, after encountering severe weather conditions including hail, the crew requested and received clearance for a 180-degree turn. During the execution of this right turn, the aircraft entered an extreme upset. The plane rolled to the right beyond 90 degrees and pitched its nose downward to roughly 40 degrees.
In an attempt to recover from this unusual attitude, the crew initiated maneuvers that subjected the airframe to forces of 4.35 g. This intense stress caused a failure in the right wing, leading the aircraft to break apart at an altitude of 6,750 feet. The wreckage crashed and caught fire shortly thereafter. There were 85 fatalities and no survivors from the flight.
Findings
The investigation determined that the structural failure was caused by the airframe being stressed beyond its ultimate strength limits during recovery maneuvers. This occurred while the aircraft was attempting to correct an unusual attitude induced by heavy turbulence. The decision to fly through known severe weather conditions contributed significantly to the event.