page_title: United Airlines Flight 553
section_title: Investigation
hierarchical_section_title: United Airlines Flight 553 / Investigation
caption_attribution_description: English: United Air Lines Flight 553
context_page_description: United Airlines Flight 553 was a scheduled flight from Washington National Airport to Omaha, Nebraska, via Chicago Midway International Airport. On December 8, 1972, the Boeing 737-222 serving the flight, City of Lincoln, registration N9031U, crashed during an aborted landing and go around while approaching Chicago Midway International Airport.
  The plane crashed into a residential neighborhood, destroying five houses; there was an intense ground fire. 43 of the 61 aboard the aircraft and two on the ground were killed. Among the passengers killed were Illinois congressman George W. Collins and Dorothy Hunt, the wife of Watergate conspirator E. Howard Hunt. This crash was the first fatal accident involving a Boeing 737, which had entered airline service nearly five years earlier in February 1968.
context_section_description: The National Transportation Safety Board (NTSB) was notified of the accident at 14:40 CST and immediately dispatched an investigation team to the scene. Agents of the Federal Bureau of Investigation (FBI) were on the scene about 45 minutes after the crash, before any investigators from the NTSB.
  The Flight Data Recorder (FDR) on board the aircraft was not functioning at the time of the crash due to a mechanical failure. Fortunately, the ARTS-III (Automated Terminal Radar Services) system at nearby O'Hare International Airport was in operation at the time of the accident, and saved recorded transponder data on magnetic tape. The tapes were analyzed extensively and compared to Boeing flight profile data to develop the course, speed, rate of descent, and altitudes of the plane as it made its approach to Chicago Midway.  The system had tracked the plane from a position of 55 miles (89 km) east of its antenna site to close to the crash site.
  The Cockpit Voice Recorder (CVR) was working normally and the tape in that "black box" was relatively undamaged, which enabled the NTSB to sequence it in time with the readings of ARTS-III. The NTSB then was able to determine the power output of the engines, at any given point in time, with CVR tape sound analysis.  That correlation, CVR with ARTS-III, allowed the NTSB to reconstruct the flight's performance, and to determine that the stick shaker first sounded 6 to 7 seconds after the plane leveled off at 1,000 ft (300 m) MSL (380 ft (120 m) AGL) and continued until ground impact.
  No evidence was found of sabotage or foul play.  The NTSB Report described nonsurvivors’ injuries in unusual detail, finding this “necessary” because of the allegations “injected into the publicity surrounding” the accident.  The Board’s official finding of the probable cause of the accident was the captain’s failure to exercise positive flight management.
  The Analysis section of the Report concludes with a paragraph to “emphasise”
  that the accident sequence resulted from that failure, and “reiterate[d]
  its often-expressed concern about the apparent lack of crew coordination and cockpit discipline during nonprecision approaches”.  It went on to make comparison with the then-recent Eastern Airlines hard landing at Fort Lauderdale and Southern Airways accident at Huntington Tri-State, and refers
  the reader to the Report on the Southern Airways accident which quotes in full an FAA Bulletin raising issues of training and culture.
  The CVR showed cockpit discussion of the FDR fault
  and it has since been reported
  as fact that the crew had become distracted by it.
  At 14:27 the final-descent checklist was completed and the first officer then called out "thousand feet", apparently in reference to the plane's altitude reaching 1,000 feet (300 m) MSL, a height of only 380 ft (120 m) above the ground at the eventual impact point.  According to the airline’s procedures, the First Officer should by then have been monitoring instruments, and calling out conformance to the specified descent profile, every 100 ft (30 m).  A similar 1000ft call and instrument check should have been made at a height above ground of 1000ft (1000 AGL) but had been omitted.  Ground impact occurred at 14:28.
  The NTSB sought to understand how the rapid descent had been accomplished.  From performance studies and simulator tests it was clear that the aircraft was in a high-drag configuration, rather than any of  the approach configurations specified by the airline, and the Board concluded that Flight 553 had landing gear down, flaps at 30 degrees and spoilers extended to the flight detent position.  The status indicator for the spoilers would then be showing green: the same indication as for spoilers retracted but ready to deploy automatically immediately on landing, potentially misleading the First Officer when executing the final-descent checklist urgently.  It was thus likely that when the Captain attempted to level off he failed to immediately retract the spoilers.  The aircraft lost speed, and a stall began to develop.
  Coincidentally, the Air Traff
caption: A photo of the crash site,
  taken by NTSB investigators
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