Flight 705 Crash in Miami (N724US)

Flight Details and Departure Flight 705 was a regularly scheduled service from Miami to Portland, Oregon, with intermediate stops at Chicago, Illinois, and Spokane and Seattle, Washington. The aircraft arrived in Miami at 1240 following a routine flight from Chicago. The captain reported that the only mechanical discrepancy was that the outflow valves were a little sticky, making it difficult to maintain pressurization smoothly. These valves were cleaned, and a leaking rivet at the No. 4 reserve fuel tank was plugged during the turnaround. The computed takeoff gross weight was 175,784 pounds, and the center of gravity was 25 percent mean aerodynamic chord, both within allowable limits. The flight departed Miami with an Instrument Flight Rules clearance at 1335. In accordance with the pilot's request for a southeast vector, a left turn was made after takeoff from runway 27L, and circuitous routing was utilized with radar vectors from Miami Departure Control to avoid anticipated turbulence associated with thunderstorm activity. A similar departure pattern had been previously flown by another flight. While maintaining 5,000 feet and a heading of 300 degrees, Flight 705 requested clearance to climb to a higher altitude. After a discussion with the FAA radar departure controller about storm activity, the flight advised that they were in the clear and could see the weather ahead, which looked pretty bad. At 1343, Flight 705 was cleared to climb to flight level 250. The controller asked if 270 degrees was their selected climbout heading, and the flight replied that this would take them out in the open again. Following some discussion about the severity of the turbulence, which was described as moderate to heavy, the flight advised that the rest of the flights should be run off the other way. At 1345, radar service was terminated, and control of Flight 705 was transferred to Miami Air Route Traffic Control Center. When the flight did not establish radio communication with the center 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 Air Route Traffic Control Center requested position and altitude, the flight replied that they were just out of 17,500 feet and would standby on the DME one. This transmission ended at 1348 and was the last known communication with Flight 705. The voice transmissions from the flight were made by the first officer. ## Witness and Crew Reports 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. Statements were received from the crews of four other flights operating in the Miami area at the approximate time of the accident. The first, in a large jet which approached Miami from the west at 7,000 feet, reported the weather as in and out of broken clouds and light rain showers with light turbulence. Darker heavy shower activity was observed to the south. They observed no small cells on their radar scope, only a broad rain area. Another crew, in a four-engine aircraft, departed Miami at 1318 via a departure pattern similar to that which Flight 705 later followed. They described the worst turbulence as medium to moderate from west of the airport to north of the Miami VORTAC. They were maintaining 5,000 feet at the time. A third crew in a 720B was flying southeast of Miami at 13,000 feet. They observed numerous rain cells on radar in the Miami area and encountered light ice at this altitude. The fourth crew, also flying a large jet, taxied out shortly after Flight 705 but delayed takeoff for nearly an hour because of the weather. ## Weather Conditions The weather in the Miami area at the time of the accident was characterized by a pre-frontal squall line approximately 250 miles in length, oriented on a northeast-southwest line immediately northwest of Miami. The U.S. Weather Bureau radar observation at Miami at 1344 indicated a broken area of thunderstorms associated with this line, with cells two to twenty miles in diameter, and tops of detectable moisture at 30,000 feet. The line was moving southeast at eight knots, and moderate rain showers were occurring at the station. The 0600 and 1800 Miami radiosonde ascents showed the freezing level to have been at 11,100 and 12,400 feet mean sea level, respectively. SIGMET No. 3, prepared by the U.S. Weather Bureau at Miami and valid from 0900 to 1300, forecast moderate to severe turbulence in thunderstorms, with a chance of extreme turbulence in heavier thunderstorms. This advisory was called to the attention of the crew of Flight 705 by the operations agent at Miami and was attached to their dispatch papers. SIGMET No. 4, valid from 1300 to 1700, was not received until approximately 1315, after the crew of Flight 705 had left the operations office. It forecast moderate to severe turbulence but deleted the reference to extreme turbulence indicated in SIGMET No. 3. Since the dispatcher for this flight was stationed in Minneapolis, the physical limitations involved made it difficult to apprise the crew of this latest advisory prior to their taxi time of 1325. ## Outcome The aircraft was completely destroyed by impact forces, and all 43 occupants were killed.