Air Midwest Flight 5481

The overnight elevator adjustment

During the night of 6 January and the morning of 7 January 2003, N233YV underwent a detail six maintenance check at Huntington, West Virginia. Air Midwest contracted with Raytheon Aerospace to provide maintenance personnel and inspectors. Raytheon Aerospace obtained mechanics through Structural Modification and Repair Technicians. A quality assurance inspector was training two mechanics during the check, and neither mechanic had previously performed the complete inspection.

One mechanic was assigned to check the elevator control cable tensions. After measuring low tension, he adjusted the cables under the inspector's supervision. The maintenance record recorded the adjustment and a normal operational check. The mechanic had experience with flight control rigging on another aircraft type, but this was his first such work on the Beech 1900D. The inspector left him unsupervised during the cable inspections and turnbuckle adjustments while attending to other duties.

The mechanic and inspector agreed to bypass several parts of the elevator rigging procedure. The manual contained no separate procedure for adjusting cable tension alone. Nine applicable steps were skipped, including calibration of the recorder pitch position sensor. That calibration called for an elevator setting of 14 degrees nose down. After the adjustment, the elevator could reach only about 7 degrees nose down. The NTSB found that completing the calibration would likely have exposed the error.

Nine flights with the restriction

N233YV returned to service on the morning of 7 January and flew nine legs before the accident. The accident pilots operated six of those legs. Another crew flew the aircraft to Lynchburg that evening and back to Charlotte the following morning, arriving at 07:15. The crews interviewed after the accident described no unusual handling during those flights.

The control geometry made the maintenance error difficult to detect during ordinary checks. The elevator rested at a shallower downward angle, but its position high above the ground limited the usefulness of an external inspection. Investigators comparing a correctly rigged aircraft with a deliberately misrigged test configuration saw no conspicuous difference from the ground. The total control-column travel decreased by about one inch, and the neutral position shifted forward by about 0.72 inch.

Three pilots qualified on the Beech 1900D also performed control sweeps in the two configurations without reporting a noticeable change in feel or position. The NTSB concluded that the changes were not conspicuous to flight crews. The nine earlier flights had more forward centers of gravity than flight 5481. Their loading demanded less nose-down elevator authority, although the restricted travel still created a potentially dangerous condition.

Loading at Charlotte

On 8 January, flight 5481 was scheduled to carry passengers from Charlotte-Douglas International Airport to Greenville-Spartanburg International Airport in Greer, South Carolina. Air Midwest operated the service as US Airways Express under Part 121. Nineteen passengers and two pilots boarded the aircraft. Conditions at Charlotte were suitable for visual flight.

The dispatch release allowed a maximum of 32 bags. A ramp agent reported 23 checked bags and eight carried to the aircraft. He told investigators that two checked bags seemed particularly heavy and that he mentioned them to the captain. The bags had no heavy-bag tags, and their additional weight was absent from the loading paperwork. Investigators found that the ramp agents handled the baggage according to company procedures.

The crew calculated the load using the airline's average passenger and baggage weights. The manifest showed a takeoff weight of 17,028 pounds and a center of gravity at 37.8 percent of mean aerodynamic chord, a reference distance used to describe the balance position along the wing. Both figures fell inside the certified limits of 17,120 pounds and 40 percent. The NTSB later determined that the aircraft actually weighed about 17,700 pounds and that its center of gravity was about 45.5 percent. Flight 5481 had the most aft loading of the ten flights since maintenance.

The takeoff and steep pitch increase

The flight left the gate about 08:30 with the captain flying. Beginning about 08:35:16, the crew checked elevator movement. The recorder measured the position of the control column. Following the maintenance adjustment, that measurement no longer represented the actual elevator angle accurately. The preflight movement corresponded to full nose-up elevator travel but only about 7 degrees nose down.

At about 08:46:18, the tower cleared flight 5481 to take off from runway 18R and instructed a right turn to heading 230 degrees. The first officer set takeoff power at the captain's request. As the aircraft accelerated through 102 knots, the elevator was near its restricted nose-down limit. The nose began rising as the elevator moved toward neutral. Nose-down trim movement followed, and the captain called for the landing gear to be raised.

At about 08:47:03, with the aircraft approximately 90 feet above the ground, the captain asked the first officer for help. The recorded pitch attitude was about 20 degrees nose up and the airspeed was 139 knots. The recorder showed forceful nose-down commands as both pilots tried to lower the nose. A sound similar to the stall warning began around 08:47:10. At about 08:47:13, the aircraft reached its maximum recorded pitch attitude of 54 degrees nose up.

Loss of control and impact

The captain transmitted an emergency call at about 08:47:16. The aircraft's nose then fell through the horizon. By about 08:47:19, it was approximately 1,150 feet above the ground, with a maximum recorded left roll of 127 degrees and a minimum airspeed of 31 knots. A second later, the recorded pitch attitude was about 42 degrees nose down.

The crew continued moving the controls as the aircraft descended. The captain called for the power to be reduced. The aircraft rolled through wings level and then to the right. At the end of the recording, its pitch attitude was 47 degrees nose down and its bank was 66 degrees right. The final recorded column position corresponded to full nose-up elevator.

The aircraft struck a US Airways maintenance hangar and came to rest approximately 1,650 feet east of the runway centerline and 7,600 feet beyond the runway threshold. Impact and fire destroyed it. All 19 passengers and both pilots died. One US Airways mechanic on the ground was treated for smoke inhalation. The first airport firefighting unit arrived about one minute and 42 seconds after the alarm. The NTSB found the emergency response timely and effective and determined that the occupants experienced impact forces beyond human tolerance.

Reconstructing the elevator and the load

The recovered elevator cable turnbuckles had markedly different lengths. The nose-down turnbuckle measured 7.30 inches between its tooling holes, compared with 5.54 inches for the nose-up turnbuckle. Ground tests reproduced restricted downward elevator movement with turnbuckles adjusted to the recovered lengths. Recorder data from before and after maintenance also showed a shift of about 9 degrees between the indicated column position and the reconstructed elevator position.

Investigators used aircraft certification data, ground tests and flight simulations to establish the available control authority. At the accident loading, a controlled takeoff and climb required about 9 to 10 degrees of nose-down elevator. Only about 7 degrees were available. The NTSB concluded that the combination of the aft center of gravity and the restricted elevator made the aircraft uncontrollable in pitch.

For loading, investigators compared the airline calculation with a component buildup and a model of the takeoff ground roll. Recovered baggage was dried before weighing because firefighting foam had increased its weight. The buildup established a minimum takeoff weight of 17,443 pounds and a center of gravity at 43.3 percent of mean aerodynamic chord. The validated ground-roll model produced the higher estimate of 17,700 pounds, with an uncertainty of 200 pounds, and a center of gravity at 45.5 percent, with an uncertainty of 2 percentage points.

Maintenance and loading oversight findings

The quality assurance inspector had trained the mechanic and then inspected his work. The NTSB found that this arrangement compromised the independence of the required inspection. It also found inadequate supervision and training during the adjustment. A complete functional check, with a person at the tail measuring elevator movement while another person moved the cockpit controls, would have provided another opportunity to find the restriction.

Air Midwest remained responsible for the airworthiness of aircraft maintained by its contractors. Its sole representative at Huntington normally worked the day shift while the maintenance was performed overnight. The investigation found inadequate airline oversight and weaknesses in the training records, procedures and internal surveillance program. The FAA had repeatedly identified serious maintenance training deficiencies before the accident but failed to pursue their correction aggressively.

The loading program had a separate set of errors. The average passenger on flight 5481 weighed 185 pounds, compared with the 175-pound figure assigned in the airline's program. Baggage weight was understated by at least 124 pounds. The NTSB found the FAA average weight assumptions incorrect and the safety margins in average weight programs inadequate to ensure compliance with aircraft limits. Its final probable cause combined the incorrect elevator rigging with the substantially aft center of gravity and identified airline, inspection and FAA deficiencies as contributing factors.

Changes and recommendations

In February 2003, Air Midwest reassigned its regional maintenance site managers to night shifts. Raytheon added a postmaintenance functional check to its revised elevator rigging procedure on 12 February. Air Midwest revised its detail six work card in July, explicitly directing mechanics to perform the complete rigging procedure whenever the cable tensions required adjustment.

The FAA requested passenger and baggage weight surveys from operators of 10-to-19-passenger-seat aircraft using average weight programs. All 15 participating operators using those programs adjusted one or more weight categories. The NTSB continued to find unacceptable errors in hypothetical loading calculations using Air Midwest's revised program. In its final report, adopted on 26 February 2004, the Board recommended complete functional checks after maintenance on critical flight systems, independent required inspections, stronger oversight of contractors and detailed training requirements. It also called for periodic weight sampling, weight and center of gravity safety margins, and research into systems capable of providing actual aircraft weight and balance data before dispatch.