29 Years ago today: On 19 July 1989 a United Air Lines McDonnell Douglas DC-10-10 crashed at Sioux City-Gateway, IA following controlling problems; killing 111 out of 298 on board.

Date:Wednesday 19 July 1989
Type: McDonnell Douglas DC-10-10
Operator:United Airlines
C/n / msn:46618/118
First flight:1973
Total airframe hrs:43401
Engines:General Electric CF6-6D
Crew:Fatalities: 1 / Occupants: 11
Passengers:Fatalities: 110 / Occupants: 285
Total:Fatalities: 111 / Occupants: 296
Aircraft damage:Destroyed
Aircraft fate:Written off (damaged beyond repair)
Location:Sioux Gateway Airport, IA (SUX) (   United States of America)
Crash site elevation:335 m (1099 feet) amsl
Phase:Landing (LDG)
Nature:Domestic Scheduled Passenger
Departure airport:Denver-Stapleton International Airport, CO (DEN/KDEN), United States of America
Destination airport:Chicago-O’Hare International Airport, IL (ORD/KORD), United States of America

United Flight 232 departed Denver at 14:09 CDT for a flight to Philadelphia. Cruising altitude was FL370. About 1 hour and 7 minutes after takeoff the crew heard a loud bang, followed by vibration and a shuddering of the airframe; the no. 2 engine had suffered an uncontained failure. It then appeared that the hydraulic pressure was zero. The DC-10 didn’t respond anymore to flight control inputs and the descending right turn was arrested by using no. 1 engine power reduction. The air driven generator (ADG), which powers the no. 1 auxiliary hydraulic pump, was deployed but hydraulic power couldn’t be restored. An emergency was declared at 15:20, and vectors to Sioux City were given by Minneapolis ARTCC. An off-duty training check airman was travelling on Flight 232 and offered his assistance. He was asked to manipulate the throttles to control pitch and roll, which was difficult because the plane had a continuous tendency to turn to the right The no. 1 and 3 thrust levers couldn’t be used symmetrically, so he used two hands to manipulate the throttles. Sioux City Airport was sighted at 9 miles out, but the aircraft was aligned with the closed runway 22 (6600 feet long) instead of the longer (8999 feet) runway 31. Given the position and the difficulty in making left turns, the approach to runway 22 was continued. The aircraft approached with a high sink rate (1620 feet/min for the last 20 seconds) at an airspeed of 215 knots. At about 100 feet above the ground the nose began to pitch downward and the right wing dropped. The plane touched down on the threshold slightly left of the centreline, skidded to the right and rolled inverted. The DC-10 caught fire and cartwheeled.

Probable Cause:

PROBABLE CAUSE: “The National Transportation Safety Board determines that the probable cause of this accident was the inadequate consideration given to human factors limitations in the inspection and quality control procedures used by United Airlines’ engine overhaul facility which resulted in the failure to detect a fatigue crack originating from a previously undetected metallurgical defect located in a critical area of the stage 1 fan disk that was manufactured by General Electric Aircraft Engines. The subsequent catastrophic disintegration of the disk resulted in the liberation of debris in a pattern of distribution and with energy levels that exceeded the level of protection provided by design features of the hydraulic systems that operate the DC-10’s flight controls.”