What happened
On a day characterized by significant convective activity, Flight 705 arrived in Miami from Chicago for a scheduled turnaround. Before departure, maintenance crews addressed minor issues, including cleaning sticky outflow valves and plugging a leaking rivet in the No. 4 reserve fuel tank. The aircraft's takeoff weight and center of gravity were within approved operational limits.
Following its 1335 departure from runway 27L under Instrument Flight Rules, the crew utilized radar vectors to navigate around heavy thunderstorm activity. While climbing through 5,000 feet, the flight crew requested an increase in altitude to flight level 250. During coordination with Miami Air Route Traffic Control Center, the crew noted visible severe weather ahead. After discussing the intensity of the turbulence, the aircraft was cleared to climb on a heading of 270 degrees.
At 1345, radar services were terminated and control was transferred to the Miami ARTCC. The last communication from the aircraft occurred at 1348, with the first officer reporting the aircraft was passing through 17,500 feet. Shortly thereafter, witnesses near the area reported hearing a loud explosion followed by a ground tremor. An orange fireball was observed descending through the clouds and disappearing behind trees. The Boeing 720 (implied via context of similar fleet operations) was destroyed upon impact, resulting in 43 fatalities.
Findings
Weather observations at the time indicated a massive pre-frontal squall line moving southeast across the region, containing thunderstorm cells with tops reaching 30,000 feet. While an earlier weather advisory had warned of potential extreme turbulence, the most recent SIGMET was not received by the crew before their taxi time due to communication delays between the dispatch office and the aircraft.
Witnesses in the vicinity reported heavy rainfall and observed the aircraft's descent following a visible explosion in the sky.