United Airlines Flight 553

Infobox Airliner accident|name=United Airlines Flight 553
Date=December 8, 1972
Type=Pilot error
Site=Chicago, Illinois
Fatalities=45 (2 on the ground)
Injuries=16
Aircraft Type=Boeing 737-222
Operator=United Airlines
Tail Number=airreg|N|9031U|disaster
Passengers=55
Crew=6
Survivors =18

United Airlines Flight 553, registration airreg|N|9031U|disaster, "City of Lincoln", was a Boeing 737-222 en route from Washington National Airport to Omaha, Nebraska via Chicago Midway International Airport on December 8 1972. After the crew was told to go around and abort their first landing attempt on runway 31L, the aircraft struck trees and then roofs along West 71st Street before crashing into a house in the 3700 block of West 70th Place. A total of 45 people were killed in the accident, 43 of them on the plane.

The three-man flight crew died and the three flight attendants survived. 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. The only person to survive in the forward part of the plane ahead of the wing was the First Class flight attendant. Her jumpseat collapsed, and she was severely injured in the crash. Fifteen passengers and the other two flight attendants in coach survived.

Among the passengers killed were Illinois Congressman George W. Collins and Watergate conspirator E. Howard Hunt's wife, Dorothy Hunt. Also killed was Michele Clark, a correspondent for CBS News. Clark was one of the first female African-American network correspondents.

Investigation

The accident was, at the time, one of the most investigated airplane crashes in history. Mrs. Hunt's purse contained $10,585 in cash and she had purchased flight insurance for $250,000 prior to boarding the flight. Conspiracy theorists believed the plane was targeted by government agencies. The Federal Bureau of Investigation assisted the National Transportation Safety Board (NTSB) in its investigation when claims surfaced that the flight was possibly sabotaged. The office of the Cook County Medical Examiner convened a coroner's jury and launched a parallel investigation. Some have claimed the FBI withheld or destroyed evidence. [http://www.rollingstone.com/politics/story/13893143/the_last_confessions_of_e_howard_hunt/2 The Last Confessions of E. Howard Hunt : Rolling Stone ] ] Nixon administration figure Chuck Colson told TIME magazine that "I don't say this to my people. They'd think I'm nuts. I think the CIA killed Dorothy Hunt."The Yankee and Cowboy Way, by Carl Oglesby, Berkley Medallion Books, New York, 1977, p. 227, citing Time for July 8, 1974.] [http://www.time.com/time/magazine/article/0,9171,943904-1,00.html "Colson's Weird Scenario"] July 8, 1974, TIME Magazine. Accessed January 26, 2007.] 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. [http://www.time.com/time/magazine/article/0,9171,943904-1,00.html "Colson's Weird Scenario"] July 8, 1974, TIME Magazine. Accessed January 26, 2007.]

The NTSB found that 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. AGL.

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.

It was a classic pilot-error accident, compounded by poor crew coordination and discipline. The plane was descending too fast, at too low of an airspeed, to be within the required "stabilized approach" parameters. Ironically, that situation was created by the fact that the plane was too fast and too high just prior to reaching the Outer Marker Beacon. The plane was 700 feet too high when it finally passed over that OMB. At that point, the pilot was required to initiate a missed approach procedure. However, the Captain, who was the pilot flying the plane, chose to continue the approach. When he finally did call for go-around thrust, it was too late. The plane entered the stall regime and then crashed before the pilot was able to effect a recovery.

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 further increased drag while decreasing lift.

Thirty-three years later to the day, in 2005, Southwest Airlines Flight 1248 skidded off the same runway, now designated 31C, at Midway Airport and onto a residential street.

United still flies a flight under the 553 designation; currently this route is from Chicago O'Hare International Airport (ORD) to Minneapolis-St. Paul International Airport (MSP).

References

External links

* [http://www.chipublib.org/004chicago/disasters/flight533_crash.html Chicago Public Library MRC Listing: Crash of United Airlines Flight 553]
* [http://amelia.db.erau.edu/reports/ntsb/aar/AAR73-16.pdf NTSB report on United Air Lines Inc. Flight 553]

ee also

Runway overshoots

* Southwest Airlines Flight 1248
* Air France Flight 358