Northwest Orient Airlines Flight 706
|Date||September 17, 1961|
|Site||Chicago, Illinois, US
|Aircraft type||Lockheed Electra|
|Operator||Northwest Orient Airlines|
Northwest Orient Airlines Flight 706, registration N137US, was a Lockheed L-188 Electra aircraft which crashed on take-off from Chicago's O'Hare International Airport September 17, 1961. All 37 on board were killed in the accident.
Flight 706 began its day in Milwaukee, Wisconsin, and was scheduled to stop at Chicago before travelling to Tampa, Fort Lauderdale, and Miami, Florida. It arrived at Chicago in the early morning and left soon afterwards, being cleared for takeoff at 8:55 AM. Takeoff was normal until the aircraft reached the altitude of 100 feet above ground level, when witnesses noticed a slight change in the sound of the Electra's engines. The aircraft began a gentle bank to the right as the starboard wing began to drop. The bank angle increased to 35°; at that point the tower controllers picked up a garbled broadcast believed to be from the pilots. The aircraft climbed to approximately 300 feet but continued to bank, eventually reaching a bank angle of over 50°. At that point, the starboard wing nicked a series of high-tension power lines running along the south boundary of the airport; shortly after that, the aircraft struck an embankment and cartwheeled onto its nose, sliding tailfirst along a stand of trees before exploding into a ball of flame among the trees. The accident took less than two minutes from the beginning of takeoff until the final crash.
Investigators with the Civil Aeronautics Board determined that the cable physically connecting the first officer's control wheel to the aileron boost unit had disconnected. This had caused the ailerons to put the aircraft in a starboard-wing-down attitude, and had prevented the pilots from being able to correct the bank. The cables attaching the pilots' control wheels to the aileron boost unit had been removed two months before the accident during routine maintenance; a safety cable that held part of the assembly together had not been replaced when the cables were hooked back up. The contact slowly separated, eventually completely failing during the takeoff sequence.
See also 
- Aircraft Accident Report on Flight 706 from the Department of Transport's Special Collections
- Accident description at the Aviation Safety Network
- Air Disaster, Vol. 4: The Propeller Era, by Macarthur Job, Aerospace Publications Pty. Ltd. (Australia), 2001 ISBN 1-875671-48-X