July 19, 1989: Human Heroics Overcome Aircraft Failure in Sioux City
- 12:00 am |
1989: A catastrophic hydraulic-system failure forces a plane to make an emergency landing in Sioux City, Iowa. The right wing catches on the tarmac, sending the plane careening down the runway in a ball of flame and twisting wreckage. But thanks to the skill of the flight team, the rescue personnel on the ground and several lucky coincidences, over half the passengers survive.
United Flight 232, a McDonnell Douglas DC-10, took off from Stapleton Airport in Denver at 2:09 p.m., bound for Chicago. At 3:16, when the DC-10 was making a slight right turn at 37,000 feet, the fan disk on the tail-mounted No. 2 engine disintegrated. Shrapnel and debris ripped through the tail section, puncturing the horizontal stabilizer and severing all three hydraulic lines, allowing fluid to bleed out.
The ailerons, stabilizers, flaps, rudder — really any component that controlled the movement of the aircraft — were now completely unresponsive. Prior to this accident, it was thought that a complete hydraulic system failure aboard a DC-10 was impossible, because two backup systems were placed far apart within the fuselage.
One of these could take over in the event one or even two of the other systems became incapacitated. However, all three hydraulic lines were routed through a single 10-inch wide opening in the tail — right where shrapnel from the explosion penetrated and severed all three lines.
The moment the accident occurred, Capt. Alfred C. Haynes, First Officer William Records, and Flight Engineer Dudley Dvorak felt a jolt and saw warning lights indicating the No. 2 engine was malfunctioning. It was at this point Records noticed that the plane was off course and moved to correct.
When he attempted to maneuver the jet, he found the controls had absolutely no response. The 120-ton vessel loaded with 296 people was hurtling more 6 miles above the ground, and there was no way to control it.
Then things got worse.
The initial failure of the No. 2 engine and subsequent explosion caused the plane to oscillate and lose altitude. Captain Haynes knew the situation was extremely dire: If the DC-10 did not land soon, it would eventually go completely out of control and crash. He contacted the nearby Sioux City Gateway Airport to coordinate an emergency landing.
But how to do it?
As luck would have it, Dennis E. Fitch, a United DC-10 flight instructor was aboard. He offered to help the crew, who had found that the throttles for the two intact engines still responded. Using differentiating thrust (decreasing power to one engine, while increasing it to the other) they discovered they could crudely maneuver the plane as well as decrease altitude.
Fitch also manually lowered the landing gear, hoping this action would pump some remaining hydraulic fluid back into the system and restore a small amount of control. It didn’t work. The crew contacted United’s San Francisco maintenance base for help, but because of the cataclysmic nature of the accident, they, too, were unable to help.
Haynes was a seasoned pilot with more than 30 years of flight experience at the time of the incident. He knew how deadly the situation looked, but continued to keep his composure, even joking with air traffic controllers during the emergency.
The crew scrambled to prep for a rough landing. They dumped fuel and made a series of right-handed turns (it was easier for the crew to steer the plane in this direction) to line up with the relatively short 6,600-foot runway 22 at Sioux City.
Meanwhile, emergency crews gathered on the runway. Because the accident happened during shift changes at the regional trauma center and the regional burn center in Sioux City, there was nearly double the normal roster of medical personnel available to treat victims.
In addition, the Iowa National Guard happened to be on duty at the Sioux City Gateway Airport. That added another 285 people trained in triage and evacuation to help out.
As flight 232 began its final descent about 45 minutes after the trouble began, Fitch manipulated the throttle to bring the aircraft down. But because of the loss of all hydraulics, the crew could not control the wing flaps to reduce airspeed effectively.
The DC-10 approached the runway traveling about 276 miles per hour. Safe landing speed for a DC-10 is about 160 miles per hour.
The plane was leaning to its right as it landed. The right wingtip struck the runway first, rupturing the fuel tank, which immediately ignited.
The tail section sheared off at impact, while the rest of the plane skittered across the runway, tearing the fuselage apart and ripping the right landing gear off. The right wing was torn completely away and tumbled end-over-end in a brilliant exploding fireball. Some eyewitnesses perceived this as the plane “cartwheeling” down the runway, but this was ultimately determined to be a misinterpretation.
There were a total of 296 people on board flight 232. Of these, 112 died. Most deaths were caused by blunt-impact force form the crash itself, while others came from smoke inhalation that occurred after the wings caught fire. Survivors tended to be seated behind first class but ahead of the wings.
Strangely, some passengers walked away from the wreckage without a scratch. Others suffered moderate-to-severe injuries, with one passenger dying from his wounds a month later.
The entire flight crew, including Fitch, survived as well. The cockpit was torn off from the rest of the fuselage and ended up nose down and partially buried in a cornfield. It took rescuers 30 minutes to extract the badly injured pilots.
National Transportation Safety Board investigators determined the accident was triggered by a faulty maintenance technique used by United Airlines. It turned out the fan disk had a significant crack in it that escaped detection because of human error.
United Airlines reworked the maintenance technique to detect flaws and cracks in fan blades. Additionally, the hydraulic systems of newer aircraft were fitted with fuses that would seal off the punctured section and prevent a total loss of fluid. These fuses were retrofitted to some DC-10s to prevent such an incident occurring again.
The NTSB report commended the flight crew, saying they “greatly exceeded reasonable expectation.” Had it not been for the quick actions of Haynes and the resourcefulness of his crew, the loss of life could have been much, much greater. When technology fails because of human error, it takes the very best in human ingenuity to overcome it.
Image: The United Flight 232 aircraft makes its final descent with damage to its horizontal stabilizer and fuselage tail cone.
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