United Airlines Flight 232 - Chronology of The Flight

Chronology of The Flight

The flight took off at 14:09 (CDT) from Stapleton International Airport, Denver, Colorado, bound for O'Hare International Airport in Chicago, with ongoing service to Philadelphia International Airport. At 15:16, while the plane was in a shallow right turn at 37,000 feet, the fan disk of its tail-mounted General Electric CF6-6 engine failed and disintegrated. The debris from the failed disk was not contained by the engine's nacelle, a housing that protects the engine. Pieces of the structure penetrated the aircraft tail section in numerous places, including the horizontal stabilizer. This shrapnel punctured the lines of all three hydraulic systems, allowing the fluid to rapidly drain away.

Captain Alfred C. Haynes and his flight crew, First Officer William Records, and Second Officer Dudley Dvorak, flight engineer, felt a jolt go through the aircraft. Warning lights illuminated which indicated that the autopilot had disengaged and the tail-mounted number two engine was malfunctioning. Captain Haynes watched First Officer Records place his hands on the flight controls in response to the autopilot disconnecting and therefore focused his attention on the malfunctioning engine. Second Officer Dvorak obtained the engine failure checklist and read the first item: throttle power must be reduced to idle. Haynes was unable to move the throttle; the linkage had been jammed as a result of the engine failure. The second item called for the fuel supply lever to be pulled to shutoff, but it would not move either. At this point, at Dvorak's suggestion, the firewall shutoff valve was actuated, and the fuel flow to the engine was shut off. This part of the emergency took 14 seconds.

Meanwhile, Records noticed that the airliner was off course, and moved his control column to correct this, but the plane did not respond. Records reported to Captain Haynes that he could not control the airplane. Haynes, having just shut off the fuel supply to the malfunctioning engine, looked at Records and was surprised by what he saw: Records had the control column turned all the way to the left, commanding maximum left aileron, and pulled all the way back, commanding maximum up elevator. These inputs would never be utilized simultaneously in normal flight. What was more, despite these inputs, which command a roll to the left and the aircraft's nose to rise, the aircraft was instead banking to the right with the nose dropping. Haynes took the flight controls and attempted to level the aircraft with his own control column. When this was ineffective, both Haynes and Records utilized their control columns at the same time in an attempt to recover from the steepening bank. The aircraft still did not respond. Out of options, and in danger of the aircraft rolling into a completely inverted position (an unrecoverable situation which would result in a crash), the crew took the throttle for the left wing mounted number 1 engine and reduced the power to idle, while also taking the throttle for the right wing mounted number 3 engine and commanding maximum power. The resulting differential thrust (no power on the left side and maximum power on the right side) caused the airplane to slowly level out.

With the imminent danger over for the time being, the crew began to diagnose the situation on the flight deck. Dvorak discovered that the pressure gauges and quantity gauges on his instrument panel for the three hydraulic systems were registering zero, and reported this to Haynes. The three hydraulic systems were separate; a single event in one system would not disable the other systems, but lines for all three systems shared the same 10-inch-wide (250 mm) route through the tail where the engine debris had penetrated. There was no additional backup system. The flight crew quickly realized that the initial failure had left all hydraulic systems, and therefore all control surfaces, inoperative. The crew called United Airlines' maintenance base using one of their radios, but as a total loss of hydraulics on the DC-10 was considered "virtually impossible", there were no procedures or guidelines for dealing with such an event.

Because of the damage in the tail, the plane had a continual tendency to turn right, and without flight controls it was difficult to maintain a stable course. The plane began to slowly oscillate vertically in a phugoid cycle, which is characteristic of planes in which control surface command is lost. With each iteration of the cycle the aircraft lost approximately 1,500 feet (460 m) of altitude. Dennis E. Fitch, an off-duty United Airlines DC-10 flight instructor, was seated in the first class section and, noticing the crew were having trouble controlling the airplane, offered his assistance to the flight attendants. Upon being informed that there was a DC-10 instructor on board, Haynes immediately invited him to the cockpit, hoping his instructional knowledge of the aircraft would help them regain control. Upon entering the cockpit and looking at the hydraulic gauges, Fitch determined that the situation was beyond anything he had ever faced. The flight crew, while using the engines to control the airplane, were also still trying to fly the airplane using their control columns. Haynes asked Fitch to go into the passenger cabin and see if their control inputs were having any effect on the ailerons. Fitch reported back that the ailerons were not moving at all. Despite this news, the crew would continue trying to fly the airplane with their control columns for the remainder of the flight, hopeful that it was at least having some effect. Fitch, his first task concluded, asked how he might be of further assistance. Haynes, still trying to fly the airplane with his control column while simultaneously working the throttles, asked Fitch to work the throttles instead. With one throttle in each hand, Fitch was able to mitigate the phugoid cycle and make rough steering adjustments.

Air traffic control (ATC) was contacted and an emergency landing at nearby Sioux Gateway Airport was organized.

Haynes kept his sense of humor during the emergency, as recorded on the plane's cockpit voice recorder (CVR):

Fitch: I'll tell you what, we'll have a beer when this is all done."

Haynes: Well I don't drink, but I'll sure as hell have one."

and later:

Sioux City Approach: United Two Thirty-Two Heavy, the wind's currently three six zero at one one; three sixty at eleven. You're cleared to land on any runway.

Haynes: Roger. You want to be particular and make it a runway, huh? (Haynes was alluding to the extreme difficulty in controlling the aircraft and their extremely low chances of making it to the airport at all.)

A more serious remark often quoted from Haynes was made when ATC asked the crew to make a left turn to keep them clear of the city:

Haynes: Whatever you do, keep us away from the city.

Haynes later noted that "We were too busy . You must maintain your composure in the airplane or you will die. You learn that from your first day flying."

As the crew began to prepare for arrival at Sioux City, they questioned whether they should deploy the landing gear or belly-land the aircraft with the gear retracted. They decided that having the landing gear down would provide some shock absorption on impact. However, the complete hydraulic failure left the landing gear lowering mechanism inoperative. Two options were available to the flight crew. The DC-10 is designed such that if hydraulic pressure to the landing gear is lost, it will fall down slightly and rest on the landing gear doors. Placing the regular landing gear handle into the down position will unlock the doors mechanically, and the doors and landing gear will then fall down into place and lock due to gravity. An alternative system is also available where the gear will fall into position by pulling a lever in the cockpit floor. This lever has the added benefit of unlocking the outboard ailerons, which are not used in high-speed flight and are locked in a neutral position. The crew hoped that there might be some trapped hydraulic fluid in the outboard ailerons and that they might regain some use of flight controls by unlocking them. They elected to extend the gear with the alternative system. Although the gear deployed successfully, there was no change in the controllability of the aircraft.

Landing was originally planned on the 9,000-foot (2,700 m) Runway 31. Difficulties in controlling the aircraft made lining up almost impossible. While dumping excess fuel, the plane executed a series of mostly right-hand turns (it was easier to turn the plane in this direction) with the intention of lining up with Runway 31. When they came out they were instead lined up with the shorter (6,600 ft) Runway 22, and had little capacity to maneuver. Fire trucks had been placed on Runway 22, anticipating a landing on Runway 31, so all the vehicles were quickly moved out of the way before the plane touched down.

Fitch continued to control the aircraft's descent by adjusting engine thrust. With the loss of all hydraulics, the crew were unable to control airspeed independent from sink rate. On final descent, the aircraft was going 240 knots and sinking at 1,850 feet per minute (approximately 440 km/h forward and 34 km/h downward speed), while a safe landing would require 140 knots and 300 feet per minute (approximately 260 and 5 km/h respectively). Fitch needed a seat for landing; Dvorak offered up his own, as it could be moved to a position behind the throttles. Dvorak sat in the cockpit's jump seat for landing. Unfortunately, right before touchdown, the aircraft began a downward phugoid and veered right. The flight crew had no time to react. The tip of the right wing hit the runway first, spilling fuel, which ignited immediately. The tail section broke off from the force of the impact, and the rest of the aircraft bounced several times, shedding the landing gear and engine nacelles and breaking the fuselage into several main pieces. On the final impact, the right wing was sheared off and the main part of the aircraft skidded sideways, rolled over on to its back, and slid to a stop upside-down in a corn field to the right of Runway 22. Witnesses reported that the aircraft "cartwheeled" end-over-end, but the investigation did not confirm this. The reports were due to misinterpretation of the video of the crash that showed the flaming right wing tumbling end-over-end and the intact left wing, still attached to the fuselage, rolling up and over as the fuselage flipped over.

Of the 296 people on board, 111 died in the crash. Most were killed by injuries sustained in the multiple impacts, but 35 people in the middle fuselage section directly above the fuel tanks died from smoke inhalation in the post-crash fire. Of those, 24 had no traumatic blunt-force injuries. The majority of the 185 survivors were seated behind first class and ahead of the wings. Many passengers were able to walk out through the ruptures to the structure, and in many cases got lost in the high field of corn adjacent to the runway until rescue workers arrived on the scene and escorted them to safety.

Of all of the passengers:

• 35 died due to smoke inhalation (none were in first class)
• 76 died for reasons other than smoke inhalation (17 were in first class)
• 47 were seriously injured (8 were in first class)
• 125 had minor injuries (1 was in first class)
• 13 had no injuries (none were in first class)

The passengers who died for reasons other than smoke inhalation were seated in rows 1–4, 24–25 and 28–38. Passengers who died due to smoke inhalation were seated in rows 14, 16 and 22–30. A person assigned to 20H moved to an unknown seat and died due to smoke inhalation.

One crash survivor died 31 days after the accident; he was classified according to NTSB regulations as a survivor with serious injuries.

Fifty-two children, including four "lap children" without their own seats, were on board the flight due to the United Airlines "Children's Day" promotion. Eleven children, including one lap child, died. Many of the children had traveled alone.

Rescuers initially ignored the cockpit, as it had been compressed in the crash to approximately waist high and was completely unrecognizable. It was not until 35 minutes after the crash that rescuers discovered that the debris was the cockpit and that the four pilots were still alive inside. All four recovered from their injuries and returned to work: Haynes, Records and Dvorak returned in three months, while Fitch, more seriously injured than the others, returned in 11 months.