United Airlines Flight 553

United Airlines Flight 553 was a Boeing 737-222 that crashed on approach to Chicago Midway International Airport at 2:28 p.m. CST, on December 8, 1972. After the crew was told to go around and abort their first landing attempt on runway 31L at Midway Airport, the aircraft struck trees and then roofs along W. 71st Street before crashing into a house at 3722 W. 70th Place. A total of 45 people were killed in the accident, 43 of them on the plane.

The three-man flight crew died along with 40 of the 55 passengers. The crash destroyed five houses and damaged three others, killing two people on the ground.

Among the passengers killed were Illinois Congressman George W. Collins and Dorothy Hunt, the wife of Watergate conspirator E. Howard Hunt. Also killed were Michele Clark, a correspondent for CBS News, and Dr. Alex E. Krill, a noted ophthalmologist from the University of Chicago. Clark was one of the first female African-American network correspondents.

This crash was the first fatal accident involving a Boeing 737, which entered airline service in February 1968.

Flight
United Airlines Flight 553 was a scheduled service from Washington National Airport to Omaha, Nebraska, via Chicago Midway International Airport. On December 8, 1972, the aircraft used for the flight was Boeing 737-222 City of Lincoln, registration N9031U.

The flight-deck crew consisted of captain Wendell Lewis Whitehouse, first officer Walter Coble and second officer Barry Elder. The pilots' union contract at the time compelled United Airlines to have three licensed pilots on board, even though Boeing had designed the 737 to be flown by a crew of two, instead of three.

Crash
The accident occurred as the airplane was making its final approach to Midway Airport.

The plane was descending too fast, at too low an airspeed, to be within the required "stabilized approach" parameters. That situation was created by the fact that the plane was too fast and too high just prior to reaching the Kedzie Outer Marker Beacon (OMB), 3.3nmi prior to the threshold of runway 31L. The plane was 700 feet above the minimum crossing altitude when it passed over that OMB. The captain extended the spoilers (speed brakes) and steepened the descent.

When it emerged from cloud approximately 400-500' above the ground the airplane was descending at a rate of more than 1500ft/min. This compares to a descent rate of 600-700ft/min required by the precision approach path to runway 31L, and United Airlines' recommended descent rate for the Boeing 737 of 1000ft/min. The captain leveled the plane off, and increased engine power. However, 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. The stick-shaker warning system activated 6-7 seconds after the aircraft leveled off and continued until it entered an aerodynamic stall.

It crashed into West 70th Place, approximately 1½ miles short of the runway.

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. Agents of the Federal Bureau of Investigation (FBI) were on the scene about 45 minutes after the crash, before any investigators from the NTSB. Oglesby, Carl, chapter 7. Extract of letter written by John Reed, chairman of the NTSB to FBI Director William Ruckelshaus (5th June, 1973): "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." Extract of reply from William Ruckelshaus to John Reed "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."

The Flight Data Recorder on board the aircraft had become inoperative approximately 14 minutes before the crash. Fortunately, the ARTS-III (Automated Terminal Radar Services) system was in operation at the time of the accident, and that data was saved on tapes in the Midway Control Tower. 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. The Cockpit Voice Recorder was working normally, and the tape in that "black box" was relatively undamaged. That 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) showed that the stick shaker (stall warning device attached to the pilots' control yoke) started 6 to 7 seconds after the plane leveled off at 1,000 ft MSL, and it continued until ground impact.

That ARTS-III system tracked the plane from a position of 55 miles east of its antennae site to the point when the plane was stalling at 380 ft. above ground level.

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. 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. That 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 manipulation of the flaps, from 30 degrees to 15 degrees, while the plane was still at too low of an airspeed, with spoilers extended. That was the wrong thing to do while attempting to go-around with the stick shaker activating, because it decreased lift and therefore increased the stall speed.

Conspiracy theories
The death of Dorothy Hunt led to the accident becoming caught up in the swirl of claim, counter-claim and rumor surrounding the unfolding Watergate scandal. In his book The Yankee and Cowboy War: Conspiracies from Dallas to Watergate, writer Carl Oglesby described flight 553 as "the Watergate plane crash".

Hunt's purse contained $10,585 in cash and she had purchased flight insurance for $250,000 prior to boarding the flight. Skeptics of the official government narrative speculate that the plane was targeted by government agencies and sabotage of the flight has been covered up. Foremost amongst these was Sherman Skolnick, a Chicago-based private investigator, who alleged that the aircraft had been sabotaged by the CIA This claim was echoed by Nixon's special counsel Chuck Colson in an interview with TIME Magazine in 1974. However, the same article speculated that Colson was accusing the CIA of the broad Watergate conspiracy in a desperate attempt to stave off President Richard Nixon's impeachment in the scandal, and that he may have "lost touch with reality" as he faced a prison sentence.

The day after the crash, White House aide Egil Krogh was appointed Undersecretary of Transportation, supervising the National Transportation Safety Board and the Federal Aviation Administration - the two agencies charged with investigating the airline crash. A week later, Nixon's deputy assistant Alexander P. Butterfield was made the new head of the FAA, and five weeks later Dwight L. Chapin, the president's appointment secretary, become a top executive with United Airlines. Mr. Krogh would later be convicted of complicity in the break-in of Daniel Ellsberg's psychiatrist's office along with Hunt, G. Gordon Liddy and a small cast of CIA-trained and retained Cuban black-bag specialists. Mr. Chapin was convicted of making false and/or misleading statements in connection to his involvement and spent less than a year in prison; Mr. Butterfield, who previously headed the office that secretly taped President Nixon's White House meetings in the Oval Office, was not prosecuted or convicted in the Watergate scandal.

The office of the Cook County Medical Examiner convened a coroner's jury and launched a parallel investigation. E. Howard Hunt in his "last confessions," reported in Rolling Stone Magazine, claimed the FBI withheld or destroyed evidence.