1. Flight

2. Accident
     Victims  

3. Investigation

4. Conspiracy theories

5. Notes

6. References

7. External links

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 {{nowrap|were killed.^[4][5]}} Among the passengers killed were Illinois congressman George W. Collins and Dorothy Hunt, the wife of Watergate conspirator E. Howard Hunt.^[6] This crash was the first fatal accident involving a Boeing 737, which entered airline service nearly five years earlier in February 1968.

Flight

United Airlines Flight 553 was a scheduled service from Washington National Airport to Omaha, Nebraska, via Chicago Midway International Airport. {{nowrap|The aircraft}} used for the flight was a four-year-old Boeing 737-222 City of Lincoln, registration {{airreg|N|9031U|,}}^[1]{{rp|2}} (built in 1968).

The flight-deck crew consisted of Captain Wendell Lewis Whitehouse (age 44), First Officer Walter Coble (43), and Second Officer {{nowrap|Barry Elder (31).^[1]{{rp|36}}}} {{nowrap|The captain,}} a highly experienced pilot with approximately {{nowrap|18,000 flight hours}} to his credit, had been with the airline since 1956 and had logged more than {{nowrap|2,400 flight hours}} on the Boeing 737 cockpit.^[1]{{rp|36}} First Officer Coble had more than 10,600 flight hours under his belt and Second Officer Elder had close {{nowrap|to 2,700 hours.^[1]{{rp|36}}}}

Accident

The accident occurred as the aircraft was on a northwesterly heading, on instruments, making a nonprecision final approach to Midway Airport.^[1]{{rp|1}}

At 14:24 CST, Flight 553 was cleared by air traffic control to Midway Airport on an approach to runway 31L. The localizer approach for runway 31L used an Outer Marker Beacon (OMB) named "Kedzie," located {{convert|3.3|nmi|abbr=on}} prior to the threshold of runway 31L. Under the published landing procedures, the aircraft was to maintain a minimum altitude of {{convert|1500|ft}} until it passed the OMB, at which point the flight was allowed to descend to a minimum altitude of {{nowrap|{{convert|1040|ft}}.^[1]{{rp|7}}}} Published procedures, and pilots operating under instrument flight rules, use mean sea level (MSL) as the point of reference for measuring altitude; at Midway Airport, an altitude of {{nowrap|{{convert|1040|ft}} MSL}} corresponded to an actual height above ground level (AGL) of only {{nowrap|{{convert|429|ft}}.^[1]{{rp|7}}}} The area was overcast at the time Flight 553 was due to land. A pilot landing on 31L immediately after the accident later reported that the airport was only visible below {{nowrap|{{convert|500|-|600|ft}} AGL.^[1]{{rp|7}}}}

When Flight 553 reached the Kedzie OMB, the aircraft was still at an altitude of {{convert|2200|ft}} MSL, a full {{convert|700|ft}} above the minimum crossing altitude of {{convert|1500|ft}} MSL.^[1]{{rp|26}} Realizing the aircraft was too high, the captain extended the spoilers (speed brakes) and steepened the aircraft's descent rate to {{convert|1550|ft}} per minute^[1]{{rp|26}} (in comparison with the {{convert|1000|ft}} per minute approximate rate specified^[1]{{rp|57}} by United Airlines for the final segment of a nonprecision approach;^[1]{{rp|26–27}} the descent rate required by the corresponding precision approach path was {{convert|600|–|700|ft}} per minute.{{cn|date=March 2019}}) The aircraft continued to descend at a rate of {{convert|1500|ft}} per minute, emerging from cloud {{convert|500|ft}} above the ground,^[1]{{rp|28}} until it reached its level-off altitude of {{nowrap|{{convert|1040|ft}} MSL.^[1]{{rp|26–27}}}}

At 14:27, the first officer called out "thousand feet" in reference to the plane's altitude reaching {{convert|1000|ft}} MSL, a height of only {{convert|380|ft|abbr=on}} above the ground at the eventual impact point.^[1]{{rp|15}} The captain leveled the plane off and increased engine power. The throttles were not advanced fully and, with the spoilers still extended, did not provide enough thrust to climb or even to maintain level flight without losing speed.^[1]{{rp|29}} The stick shaker, a stall warning device attached to the pilots' control yoke, activated 6–7 seconds after the aircraft leveled off and continued to sound as the aircraft entered an aerodynamic stall.^[1]{{rp|28}}

At 14:28, the aircraft struck trees and then roofs along W. 71st Street before crashing into a house at 3722 W. 70th Place,^[5][7] {{convert|1.89|mi|1}} southeast of the runway,^[8] in a residential area of the city's West Lawn community, one and a half blocks west of Marquette Park. {{nowrap|({{coord|41.7653|-87.716}})}}

Victims

The three-man flight crew died, along with 40 of the 55 passengers.^[1]{{rp|4}} The crash destroyed five houses and damaged three others,^[1]{{rp|5}} killing two people on the ground.^[1]{{rp|4}} Survivors credited the actions of stewardesses as heroes, as the stewardesses called out to survivors to exit the plane through a hole in the rear of the plane.^[9]

Investigation

The National Transportation Safety Board (NTSB) was notified of the accident at 14:40 CST and immediately dispatched an investigation team to the scene.^[1]{{rp|35}} Agents of the Federal Bureau of Investigation (FBI) were on the scene about 45 minutes after the crash, before any investigators from the NTSB.{{efn|Extract of letter written by John Reed, chairman of the NTSB to FBI Director William Ruckelshaus (June 5, 1973): {{quote|Our investigative team assigned to this accident discovered on the day following the accident that several FBI agents had taken a number of non-typical actions relating to this accident within the first few hours following the accident. Included were: for the first time in the memory of our staff, an FBI agent went to the control tower and listened to the tower tapes before our investigators had done so; and for the-first time to our knowledge, in connection with an aircraft accident, an FBI agent interviewed witnesses to the crash, including flight attendants on the aircraft prior to the NTSB interviews. As I am sure you can understand, these actions, particularly with respect to this flight on which Mrs. E. Howard Hunt was killed, have raised innumerable questions in the minds of those with legitimate interests in ascertaining the cause of this accident. Included among those who have asked questions, for example, is the Government Activities Subcommittee of the House Government Operations Committee.^[10]

}}}}{{efn|Extract of reply from William Ruckelshaus to John Reed: {{quote|FBI has primary investigative jurisdiction in connection with the Destruction of Aircraft or Motor Vehicles (DAMV) Statute, Title 18, Section 32, U.S. Code, which pertains to the willful damaging, destroying or disabling of any civil aircraft in interstate, overseas or foreign air commerce. The fact that Mrs. E. Howard Hunt was aboard the plane was unknown to the FBI at the time our investigation was instituted. It has been longstanding FBI policy to immediately proceed to the scene of an airplane crash for the purpose of developing any information indicating a possible Federal violation within the investigative jurisdiction of the FBI. In all such instances liaison is immediately, established with the National Transportation Safety Board (NTSB) personnel upon their arrival at the scene. Approximately 50 FBI Agents responded to the crash scene, the first ones arriving within 45 minutes of the crash ... The FBI's investigation in this matter was terminated within 20 hours of the accident and on December 11, 1972, Mr. William L. Lamb, NTSB, was furnished with copies of the complete FBI investigation pertaining to this crash after it was determined there was apparently no violation of the DAM or CAA Statutes.^[10]}}}}

The Flight Data Recorder on board the aircraft was not functioning at the time of the crash due to a mechanical failure.^[1]{{rp|8}} 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.^[1]{{rp|14–15}} Those 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.^[1]{{rp|15}} The Cockpit Voice Recorder was working normally and the tape in that "black box" was relatively undamaged,^[1]{{rp|8}} which enabled the NTSB to sequence it in time with the readings of ARTS-III.^[1]{{rp|18}} 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 {{convert|1000|ft|abbr=on}} MSL ({{convert|380|ft|abbr=on}} AGL) and continued until ground impact.

That ARTS-III system tracked the plane from a position of {{convert|55|mi}} east of its antennae site to the point when the plane stalled at {{convert|1000|ft|abbr=on}} MSL.^[1]{{rp|15}}

The official finding of the NTSB was that the probable cause of the accident was the stalling of the airplane (airspeed too low) because the captain failed to ensure that the flight remained within the required airspeed and altitude parameters for that non-precision approach profile.^[1]{{rp|32}} No evidence was ever found of sabotage or foul play.

From their performance study and simulator tests, the NTSB concluded that the spoilers must have been extended to at least the flight detent position during the rapid descent that preceded the stall. It was thus likely that when the Captain attempted to level off and then to go-around, the crew failed to immediately retract the spoilers which made it all the more difficult to recover from the stall before ground impact. Although the spoilers were found to be fully retracted in the wreckage, it was possible that the spoilers could have retracted on their own as a result of the impact forces and loss of hydraulic pressure.

The final mistake was inappropriate retraction of the flaps, from 30 degrees to 15 degrees, while the plane's airspeed was still too low, and the spoilers were extended. Flap retraction is inappropriate with the stick shaker activating because flap retraction causes an increase in stall speed.

Conspiracy theories

Dorothy Hunt's death led to the accident becoming caught up in rumors and conspiracy theories related to the unfolding Watergate scandal.^[11] Mrs. Hunt was carrying $10,000 in $100 bills when the plane crashed, and some alleged that this money was meant for people connected to Watergate.^[6][11] James McCord alleged that Mrs. Hunt supplied the Watergate defendants with money for legal expenses.^[6] The FBI's appearance at the crash scene was also regarded by some as unusually fast.^[10][11] Skeptics of the official narrative speculated that the plane was targeted due to Mrs. Hunt's presence on board, and that sabotage of the flight was covered up by government agencies. As a result, the accident became known as "the Watergate crash."^[10][11]

Proponents of Watergate-related theories included Sherman Skolnick, a Chicago-based private investigator, who alleged that the aircraft had been sabotaged by the CIA.{{efn|"Skolnick was instantaneous in charging that the crash of United flight 533 was the result of sabotage and that there was a big Watergate connection."^[10]}} On June 13, 1973, Skolnick testified at an NTSB hearing in Rosemont, Illinois and claimed the Federal Bureau of Investigation, Columbia Broadcasting System, United Airlines, traffic controllers at Midway, and the NTSB itself conspired in a plot to sabotage the flight because 12 of its passengers had links to Watergate.^[12]{{efn|According to the Chicago Tribune, Skolnick also linked the crash to "a pipeline lobby, investment scandals in Switzerland, legislative acts in Costa Rica, and underworld dealings in stolen currency."^[12]}} United Airlines officials had asked the NTSB to hear Skolnick's version because he had frequently charged that UAL was among those attempting to suppress his explanation of events.^[12] He said that Hunt carried $2 million in traveler's checks and money orders stolen from the Committee for the Re-Election of the President, $50,000 in currency, and documents that may have led to the impeachment of President Richard Nixon.^[12] He stated a hitman — that Nixon had placed aboard the aircraft to make sure that Hunt was killed — also died in the crash.^[12] The Chicago Tribune said that Skolnick "[knitted] scores of facts and assumptions together loosely" and "[no] documentation was produced to substantiate the charges".^[12]

The claim of CIA responsibility was echoed by Nixon's special counsel Chuck Colson in an interview with Time magazine in 1974.^[13] However, the same article speculated that Colson was accusing the CIA of the broad Watergate conspiracy in a desperate attempt to stave off Nixon's impeachment in the scandal, and that Colson may have "lost touch with reality" as he faced a prison sentence.^[13]

Notes

References

External links

• Cockpit Voice Recorder transcript (at tailstrike.com)

Note that tailstrike.com‘s accident summary is from this
Wikipedia article, as in December 2007, lightly copy-edited.

• FBI file on United Airlines Flight 553

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