Accident Overview
On the date of the accident, United Air Lines, Inc., Flight 389 (UAL 389) was a regularly scheduled domestic passenger/cargo flight from LaGuardia Airport, New York, to O'Hare International Airport, Chicago, Illinois. The aircraft, a Boeing 727-22 registered as N7036U, had arrived at LaGuardia earlier that day following a trip from Los Angeles, California, with stops in Sacramento, California; Reno, Nevada; Denver, Colorado; and Chicago, Illinois.
Flight Crew and Departure
The flight crew reported for duty at LaGuardia Airport one hour before the scheduled departure. They prepared for the flight to Chicago. The stewardesses arrived with the aircraft from Chicago. Persons known to have been in contact with the crew prior to departure noted nothing unusual about their behavior or appearance. UAL 389 departed LaGuardia at 1952 on an Instrument Flight Rules (IFR) flight plan, cruising at Flight Level 350 (FL 350) and estimating arrival at O'Hare at 2127.
Communication and Descent
The crew reported at FL 350 at 2011.35. At 2102, UAL 389 came under the control of the Chicago Air Route Traffic Control Center (ARTCC), reporting its altitude as FL 350. The flight was cleared to O'Hare Airport via the Pullman VORTAC direct to the Northbrook VORTAC, then direct O'Hare, and was instructed to maintain FL 350. The crew acknowledged correctly, and radar contact was established. At 2103, the ARTCC controller cleared UAL 389 to descend to FL 240 and to "start descent now through 31" (FL 310). UAL 389 replied "...down to 240, leaving three five."
At 2106, UAL 389 was cleared to continue its descent to 14,000 feet and given an altimeter setting of 29.90 inches for O'Hare. The crew acknowledged immediately and, in reply to the controller's inquiry, reported leaving FL 280 "now." At 2109, the flight was instructed to change frequencies and, within the same minute, reported out of FL 260 descending to fourteen thousand feet. This was the last altitude information received from the crew.
At 2111, the flight was cleared to descend to 6,000 feet, and the clearance was immediately acknowledged correctly. At 2118:35, control of the flight was passed to Chicago Approach Control (ORD). The radar target of UAL 389 was in the vicinity of the Sturgeon Intersection (intersection of the 011 radial of Chicago Heights and 076 radial of Northbrook VORTAC, 28 miles east of Northbrook VORTAC). At 2118:38, the target was observed approximately 2 miles east of the intersection. At 2119:36, the crew contacted ORD and was advised that radar contact had been established. At this time, the aircraft target was 2-3 miles west of Sturgeon.
UAL 389 was cleared to maintain 6,000 feet and to depart the Northbrook VORTAC on a heading of 240 degrees. The flight was advised that instrument landing system approaches were in progress on runway 14R at O'Hare and that the current O'Hare altimeter setting was 29.93. The pilot read back the altimeter setting incorrectly, the controller corrected him, and the pilot repeated it correctly. This was the last communication received from the flight, ending at 2120:03.
Crash
The airplane crashed into Lake Michigan and exploded upon impact. All 30 occupants were killed.
Probable Cause
The National Transportation Safety Board was unable to determine the reason for the aircraft not being leveled off at its assigned altitude of 6,000 feet.