It was a nasty afternoon in Miami the day of February 12, 1963. A Northwest Airlines Boeing 720, designated flight 705, was scheduled to depart at 1:30pm bound for Portland, Oregon. On the flight deck that day was Captain Roy Almquist and First Officer Robert Feller. Along with the flight engineer and five cabin attendants, only thirty-five passengers boarded for the first leg to Chicago. A squall line was lying to the northwest of the city, slowly moving southeast. Associated with this line were thunderstorm cells up to 20 miles in diameter, some reaching as high as 40,000ft. A sigmet had been issued for moderate to severe turbulence with a chance of extreme turbulence inside the storms. The crew asked for a southeast departure, hoping to go around or over the top of the worst of the weather. After heading south east initially, the aircraft was vectored back north at 5000ft. Feller called Miami, asking for a higher altitude and reporting that "We're in the clear now. We can see it out looks pretty bad." 705 was then cleared to climb to FL250 and said they would be turning 30 degrees left, giving them and approximate heading of 270 degrees. Feller then told Miami that turbulence was "moderate to heavy" and then advised them "OK, you better run the rest of them off the other way." After being handed off to Miami Centre, Feller reported that they were climbing through 17,500ft. This transmission, thirteen minutes after takeoff, was the last from 705. Shortly after, several people located in the Everglades heard a loud explosion followed by a ground tremor. One women reported seeing what looked like "a ball of flame in the edge of a cloud."
......Wreckage was strewn over some fifteen miles, indicating an in-flight break-up of the aircraft. While it was clear the weather was severe in the area, sabotage could not be ruled out nor could some other sort of component failure, the aircraft having been involved in a landing accident a few months prior.

Reconstructed Wreckage of 705

Collection of the wreckage showed that the tail surfaces had broken off downward while the forward fuselage separated upwards. All four engines had separated upward as well. Readout of the FDR showed that showed that the aircraft had encountered some heavy turbulence while climbing to 15,000ft until it turned more westerly. It then turned back northwest and began to climb again, at one point obtaining a climb rate of 9000ft/min until reaching just over 19,000ft. At this point, the vertical acceleration suddenly became negative 2gs, increasing even further with fluctuations up to negative 2.8gs, the airspeed continuing to increase as well. Vertical acceleration abruptly went back to positive 1.5gs. During it's descent, the airspeed increased until the FDR was no longer able to accurately measure it, greater than 470kts. Analysis showed that the aircraft would have reached some 22 degrees pitch up during it's dramatic climb to beyond vertical in it's final descent. Structural tests of the 720 showed that it could have withstood the initial excessive forces brought on by the thunderstorm gusts. It appeared that the aircraft did not break up until the crew apparently tried to recover when passing through 10,000ft. The question then was what caused the aircraft to get into such an unusual condition. The answer came in the fact that the aircraft has an inherit tendency to 'weathervane' into gusts. So, when the initial updraft caught the aircraft, it would have an initial tendency to nose down into the gust. This apparently prompted Almquist to give nose-up inputs, which would actually worsen the overall situation. The same effect worked in the downdraft which followed. It is also important to note that, although it appears full up elevator was used in the recovery attempt, full nose-down trim was still wound in from the prior encounter with the updraft. Boeing tests showed that recovery from the dive in this condition beyond 320kts is not possible.