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Flight 705 is regularly scheduled from Miami to Portland, Oregon, with intermediate stops at Chicago, Illinois and Spokane and Seattle, Washington. The computed takeoff gross weight of 175,784 pounds, and center of gravity (c.g.) of 25 percent mean aerodynamic chord (MAC) were both well within the allowable limits. Prior to departing the ramp at 1325, the crew asked the ground controller about the departure routes being utilized, and he replied that most flights were departing "... either through a southwest climb or a southeast climb and then back over the top of it..." The flight departed Miami with an Instrument Flight Rules (IFR) clearance at 1335. In accordance with the pilot's request for a "... southeast vector..." a left turn was made after the takeoff from runway 27L and circuitous routing was utilized in conjunction with radar vectors from Miami Departure Control, to avoid areas of anticipated turbulence associated with thunderstorm activity (See Attachment A). A similar departure pattern had been previously flown by another flight. Subsequently, while maintaining 5,000 feet and a heading of 300 degrees, Flight 705 requested clearance to climb to a higher altitude. Following a discussion between the flight and the Federal Aviation Agency (FAA) radar departure controller about the storm activity, and while clearance to climb was being coordinated with the Miami Air Route Traffic Control Center (ARTCC), the flight advised, "Ah-h we're in the clear now. We can see it out ahead... looks pretty bad." At 1343, Flight 705 was cleared to climb to flight level[1] 250 (FL250). They responded, "OK ahhh, we'll make a left turn about thirty degrees here and climb..." The controller asked if 270 degrees was their selected climbout heading, and they replied that this would take them "... out in the open again..." Accordingly, clearance was granted. Following some discussion about the severity of the turbulence, which was described as moderate to heavy, the flight advised, "OK, you better run the rest of them off the other way then."
At 1345 radar service was terminated and control of Flight 705 was transferred to Miami ARTCC. When the flight did not establish radio communication with ARTCC on the initial frequency, Departure Control provided a secondary frequency, and instructed the flight to turn to a heading of 360 degrees which was acknowledged. When Miami ARTCC requested position and altitude, the flight replied, "We're just out of seventeen five (17,500 feet) and standby on the DME one." This transmission ended at 1348, and was the last known communication with Flight 705. The voice transmissions emanating from the flight were made by the first officer.
Witnesses in the area reported that a loud explosion had occurred in the air, and several felt a subsequent ground tremor. They also reported that heavy rain had been falling in the area. One witness, in company with five other persons, was seven miles south of the main wreckage site. She heard the sound of an explosion which had no echo. When she looked in that direction she saw an orange ball of flame in the edge of a cloud. As she directed the attention of her companions toward this flame, it dropped straight down, becoming a streak, and disappeared behind trees. Shortly after the disappearance a second sound was heard.
- ↑ "ATP 7110.1A Sec. 120 - a level of constant atmospheric pressure related to a reference datum of 29.92 inches of mercury." Utilized by all aircraft operating above 23,500 feet at the time.
