1961 — Sep 17, Northwest 706, mechanical failure takeoff crash, O’Hare, Chicago IL– 37

— 37 AirDisaster.Com. Accident Database. Accident Synopsis 09171961.
— 37 CAB. AAR. Northwest Airlines…O’Hare Int. Airport, Chicago, IL, Sep 17, 1961.
— 37 Kimura. World Commercial Aircraft Accidents 3rd Ed., 1946-1993, V.1. 4-11-1994, p. 3-6.

Narrative Information

Civil Aeronautics Board: “On September 17, 1961, at 0857 c.d.t., a Northwest Airlines, Inc., Lockheed Electra, N 137US, crashed shortly after takeoff from runway 14R, at O’Hare International Airport, Chicago, Illinois. All 32 passengers and the crew of 5 sustained fatal injuries. The aircraft was totally destroyed by impact and subsequent fire.

“Flight 706 originated in Milwaukee, Wisconsin, and was a regularly scheduled flight from Milwaukee to Miami, Florida, with intermediate stops at Chicago, Illinois, Tampa, and Fort Lauderdale, Florida. While at O’Hare Airport the aircraft was routinely serviced and checked, and a scheduled crew change was made. At approximately 0855, while taxiing from the ramp, the flight was cleared for takeoff, and shortly thereafter the aircraft departed. Takeoff and Initial climb appeared to be normal, but at approximately 200 feet a shallow turn to the right continued into a gradually increasing bank of about 85 to 90 degrees. While in the turn, the crew made a short, garbled transmission indicating alarm. During the latter part of the turn a gradual descent began and, two minutes after takeoff, the aircraft struck the ground….

“The right wing near the No. 4 engine struck powerlines adjacent to the Chicago Northwestern Railroad tracks, severing the lines at an angle of about 70 degrees from the horizontal, and causing a bright bluish flash. The aircraft 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, and wreckage was strewn over an area 200 feet wide and 1,200 feet long. Evidence of ground fire was found at various points along this path.

“Impact occurred on airport property about 3,800 feet abeam and to the right of the end of runway 14R, about 500 feet north of Irving Park Road. After passing beyond the railroad embankment the aircraft was lost to view by most of the eye witnesses because of trees and other obstructions; immediately thereafter a large mushroom of orange-red flame accompanied by heavy black smoke was seen. Time of impact was established as 0857. The aircraft was demolished by impact and fire. All occupants were fatally injured….

“The preponderance of evidence shows that the following chain of events led to, and had a direct bearing on, the destruction of N 137US on September 17, 1961: At, or shortly after, the aircraft began its turn to the right following takeoff from O’Hare Airport, a failure occurred in the aileron primary control system between the boost -input quadrant and the control wheel. This failure was caused by a separation of the left wing down cable from the slack absorber on the copilot’s side. Failure at this point made it impossible for the crew to decrease the steepening bank or effect a recovery by any means at such a low altitude. In connection with the failure experienced, it was established that two months prior to the accident, during an aileron boost unit change, the cable connectors to the slack absorber terminals were unsafetied and unscrewed, and that these connectors were never tightened and resafetied before the aircraft was released for flight. During the period July 12, 1961, until the accident, it is believed that there occurred a gradual unscrewing of the connector in question until it finally separated from the slack absorber following takeoff on the flight involved….

Mention has already been made of the fact that eight aileron flight control discrepancies were reported by pilots on the logs of N 137US from June 27, to July 11, 1961, the date the aileron booster unit was removed, and that during this time the aircraft was flown on a total of 29 scheduled flights. The aircraft logs recording the corrective actions taken indicate that little effort was made to analyze the cause of these discrepancies and to correct them. This type of operation reflects a casual attitude on the part of maintenance personnel toward a potentially hazardous condition, which was also evident in the replacement of the aileron boost assembly.

“The training of Northwest Airlines line maintenance personnel on the Lockheed Electra appeared to have been sporadic and inadequate in scope, particularly with reference to flight control systems. Although the changing of this aileron boost unit provided an excellent opportunity for advantageous use of the existing on-the-job training program, this potential went unrealized.

“The Board determines that the probable cause of this accident was a 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.” (CAB. AAR. Northwest Airlines…O’Hare Int. Airport, Chicago, IL, Sep 17, 1961.)

Sources

AirDisaster.Com. Accident Database. Accident Synopsis 09171961. Accessed at: http://www.airdisaster.com/cgi-bin/view_details.cgi?date=09171961&reg=N137US&airline=Northwest+Orient

Civil Aeronautics Board. Aircraft Accident Report. Northwest Airlines, Inc., Lockheed Electra, L-188c, N 137US, O’Hare International Airport, Chicago, Illinois, September 17, 1961. Washington, DC: CAB (File No. 1-0018), December 13, 1962, 19 pages. Accessed at: http://dotlibrary1.specialcollection.net/scripts/ws.dll?file&fn=8&name=*P%3A%5CDOT%5Cairplane%20accidents%5Cwebsearch%5C091761.pdf

Kimura, Chris Y. World Commercial Aircraft Accidents 3rd Edition, 1946-1993, Volume 1: Jet and Turboprop Aircrafts. Livermore, CA: Lawrence Livermore National Laboratory, Risk Assessment and Nuclear Engineering Group. 4-11-1994.