Narrative:Lockheed Electra N137US operated on Northwest flight 706 from Milwaukee to Miami (MIA) with intermediate stops at Chicago, Tampa and Fort Lauderdale. After a crew change at Chicago the plane taxied to runway 14R at 08:55 and was cleared for takeoff. Between the 8,000 and the 9,000-foot runway marker the aircraft was observed to commence an apparently coordinated right turn with a slowly increasing rate of bank. When the bank angle was 30 to 45 degrees, the crew made a short, garbled transmission. Immediately thereafter, at a bank angle of 50 to 60 degrees, the aircraft began to lose altitude. The maximum altitude attained in the entire turn was 200 to 300 feet. The right wing struck powerlines adjacent to the Chicago Northwestern Railroad tracks, severing the lines at an angle of about 70 degrees from the horizontal. It then continued in a direction of about 271 degrees magnetic and, when in a bank of about 85 degrees and a nose-down attitude of about 10 degrees, the right wing of the aircraft struck the railroad embankment.
Continuing to roll about its longitudinal axis, the aircraft cartwheeled, the nose crashing into the ground 380 feet beyond the point of first impact, and landed right side up. It then slid tail first another 820 feet. The aircraft disintegrated throughout its path.
PROBABLE CAUSE: "Mechanical failure in the aileron primary control system due to an improper replacement of the aileron boost assembly, resulting in a loss of lateral control of the aircraft at an altitude too low to effect recovery."
This map shows the airport of departure and the intended destination of the flight. The line between the airports does not
display the exact flight path.
Distance from Chicago-O'Hare International Airport, IL to Tampa International Airport, FL as the crow flies is 1620 km (1012 miles).