What happened
On the morning of the accident, Flight 706 was cleared for departure from runway 14R. While taxiing through the runup area toward the runway, the crew performed a running takeoff. Shortly after lifting off, the Electra aircraft was observed at an altitude between 50 and 75 feet while traveling down the runway. As the plane reached the 8,000-foot marker, its altitude was estimated at approximately 100 feet, which was noted as being lower than typical for this aircraft type during this phase of flight. Witnesses reported hearing a change in engine noise during this period.
Between the 8,000 and 9,000-foot markers, the aircraft entered a coordinated right turn with an increasing bank angle. Following a brief, unclear radio transmission from the crew, the aircraft began to descend as the bank reached 50 to 60 degrees. The right wing struck powerlines near the Chicago Northwestern Railroad tracks, which caused a visible flash and severed the lines. The aircraft then struck a railroad embankment with its right wing while in a steep bank and nose-down attitude.
The aircraft subsequently cartwheeled, with the nose impacting the ground 380 feet past the initial strike point before sliding another 820 feet. The impact and subsequent fire caused the airframe to disintegrate across a debris field measuring 1,200 feet in length. The accident occurred on airport property near Irving Park Road. There were no survivors among the occupants of N137US, as all individuals on board were fatally injured.
Findings
Investigation into the crash determined that a mechanical failure in the aileron primary control system occurred. This failure was attributed to an improper replacement of the aileron boost assembly, which led to a loss of lateral control at an altitude insufficient for the crew to recover the aircraft.