United Airlines Flight 232 — A Hidden Flaw Severed Every Hydraulic Line, and a Crew Flew on Engines Alone

On 19 July 1989, United Airlines Flight 232, a McDonnell Douglas DC-10-10 registered N1819U, crash-landed at Sioux Gateway Airport in Sioux City, Iowa, after the catastrophic failure of its tail-mounted number two engine destroyed all three of the aircraft’s hydraulic systems. Of the 296 people aboard, 112 were killed and 184 survived. Unlike most entries in this file, the outcome is remembered less for the deaths than for the survivals: an aircraft left with no conventional flight controls was kept airborne for some 44 minutes and brought to a runway by a crew improvising with engine thrust alone, a feat the investigators and the wider profession regarded as extraordinary.

The aircraft had departed Denver’s Stapleton International for Chicago O’Hare, with onward service to Philadelphia. About an hour into cruise at 37,000 feet, the stage-one fan disk of the rear General Electric CF6-6 engine fractured and burst apart. The engine failed in an uncontained manner: high-energy fragments were thrown clear of the engine casing and through the tail. Those fragments cut the lines of all three independent hydraulic systems where they passed close together near the tail. Hydraulic fluid drained away, and with it went the aircraft’s ability to move its elevators, ailerons, rudder, flaps, and slats. The DC-10 was, in the conventional sense, uncontrollable.

What followed was a controlled descent flown on differential thrust. Captain Alfred Haynes and his crew, joined by an off-duty United DC-10 training check airman, Captain Dennis Fitch, who was travelling as a passenger and came forward to help, manipulated the two remaining wing engines — adding and reducing power on each side to turn, and using power changes to coax the nose up and down — to fly the crippled aircraft toward Sioux City. On final approach the aircraft was descending too fast and drifting right; the right wingtip struck the runway, the aircraft cartwheeled, broke apart, and caught fire. That so many lived through it was attributed to the crew’s airmanship, the cabin crew’s preparation, and a well-drilled local emergency response that happened to be on a shift change with extra personnel available.

The National Transportation Safety Board, in report AAR-90/06, traced the disaster to a metallurgical defect that had been present in the fan disk since its manufacture and had grown into a fatigue crack that inspections failed to catch. The board’s probable cause did not stop at the metal; it faulted the inspection and quality-control regime that should have found the crack and did not.