Checks & Balances

On January 8, 2003, Air Midwest Flight 5481, a Raytheon Beech 1900D, crashed into a hangar at Charlotte-Douglas International Airport (CLT), Charlotte, N.C. Preliminary information suggested that the weights of the passengers and baggage on the plane differed from the FAA's "average" profile. About two weeks after the accident, the agency issued a notice to all Part-121 operators of airplanes having 10 to 19 passenger seats. The operators were asked to validate the average weights of their passengers when figuring out weight-and-balance requirements for their aircraft. Operators can use average weights approved by the FAA for their weight-and-balance control programs or actual weights of passengers and baggage.

An FAA Advisory Circular updated in November 1995 said that air carriers should allow at least 180 pounds for an adult passenger in the spring and summer, and 185 pounds in the fall and winter, which includes 20 pounds per person for carry-on bags. The average weight suggested for checked baggage was 25 pounds per bag. The presumption was that the mix of passengers would be 60% male and 40% female.

When the FAA looked at the numbers gathered after the Flight 5481 accident, it found that its average number was no longer accurate. The new weight of adult passengers and their carry-on bags was 195.63 pounds, an increase of 20.63 pounds. Also, the average checked bag weighed 28.81 pounds, 3.81 pounds higher than the FAA's number. So, not only do we weigh more, we're carrying heavier baggage. The safety implications of routinely flying overweight aircraft are startling, especially when you consider that you can't be sure that center of gravity limits are maintained.

The NTSB said that inaccurate weight-and-balance calculations played a significant role in the crash of Flight 5481, compounding the problems faced by the flight crew as a result of incorrect rigging of the airplane's elevator control system. The Air Midwest (operating as US Airways Express) twin-engine turboprop crashed shortly after takeoff from runway 18R at CLT. The two flight crewmembers and 19 passengers aboard the airplane were killed, one person on the ground received minor injuries, and the airplane was destroyed by impact forces and a post-crash fire. Flight 5481 was destined for Greenville-Spartanburg International Airport (GSP), Greer, S.C. Visual meteorological conditions prevailed at the time of the accident.

The airplane had been flown from Huntington, W.Va., to CLT the day before the accident. Air Midwest records indicated that the accident pilots flew the accident airplane on six flight legs that day. Another flight crew met the accident airplane for a trip that night from CLT to Lynchburg, Va. That crew flew the accident airplane back to CLT the next morning, arriving at 7:15. According to post-accident interviews, neither the captain nor the first officer of those two flight legs noticed anything unusual about the airplane.

The dispatch release for flight 5481 showed that a maximum of 32 bags was allowed. One of the two ramp agents who were working the flight told investigators that 23 bags had been checked and that eight bags were carried on the airplane. The ramp agent stated that two of the checked bags were heavy, with an estimated weight of between 70 and 80 pounds, and that he told the captain who indicated that a child would be on board, compensating for the extra baggage weight. The ramp agent estimated that the forward cargo compartment was about 98% full by volume.

The flight data recorder (FDR) indicated that the flight crew performed a control check of the elevators. The FDR's pitch control position parameter, which measures the position of the control column, recorded values from 15 degrees ANU (airplane nose up) to 16.5 degrees AND (airplane nose down). Normal elevator travel for the Beech 1900D is from 20 to 21 degrees ANU to 14 to 15 degrees AND. The elevator neutral position is zero degrees. In a properly rigged elevator control system, the FDR pitch control position parameter accurately reflects the elevator position. However, the elevator control system had been improperly rigged, and investigators had to adjust some of the FDR's data.

At about 8:46:18, the local controller cleared Flight 5481 for takeoff and instructed the flight crew to turn right to a heading of 230 degrees after takeoff.

According to Air Midwest's Beech 1900D Performance Manual, the rotation speed during takeoff is 105 knots. By about 8:46:48, the airspeed was above 102 knots, and the elevator position was seven degrees nose down. About three seconds later, the elevator position was one degree nose down, and the pitch attitude of the airplane began to increase. After 8:46:53, the pitch trim started moving nose down, and about three seconds later, the captain called for the landing gear to be retracted. At about 8:46:57, the elevator position returned to seven degrees nose down, and about two seconds later, the cockpit voice recorder (CVR) recorded the sound of the landing gear retracting.

At about 8:47:02, the first officer stated, "Wuh," and the captain stated, "Oh." The captain then said, "Help me." At that point, the airplane was about 90 feet above ground level, and FDR data showed that the airplane's pitch attitude was 20 degrees nose up and airspeed was 139 knots.

FDR data indicated that the flight crew was forcefully trying to get the nose down, and multiple statements and sounds from both flight crewmembers associated with their efforts to push the airplane's nose down were recorded on the CVR. It also recorded a change in engine and propeller noise and, about one second later, the beginning of a sound similar to the stall warning horn.

At about 8:47:13, the FDR recorded a maximum pitch attitude of 54 degrees nose up. The captain radioed the control tower, "We have an emergency for Air [Midwest] fifty-four eighty-one." At about 8:47:18, the airplane's pitch attitude decreased through zero degrees, and the elevator position began to move nose up. The airplane was about 1,150 feet AGL, and the FDR recorded a maximum left roll of 127 degrees and a minimum airspeed of 31 knots. About one second later, the FDR recorded a pitch attitude of 42 degrees nose down. The captain said, "Pull the power back." The CVR recorded the beginning of a sound similar to the stall warning horn, which continued to the end of the recording. About 8:47:22, the airplane's roll attitude stabilized at about 20 degrees left wing down and the pitch attitude began to increase. The airplane rolled right, reaching a maximum right roll of 68 degrees and a maximum vertical acceleration of 1.9 G's. The airplane struck a US Airways maintenance hangar on CLT property and came to rest about 1,650 feet east of runway 18R's centerline and about 7,600 feet beyond the runway 18R threshold. Controllers heard an emergency locator transmitter signal beginning about 8:47:29.

Air Midwest records indicated that the captain had accumulated 1,865 hours total company flying time, including 1,100 hours as a Beech 1900D captain. She held an ATP certificate and a current first-class medical. The first officer held a commercial certificate and first-class medical, and the company reported he had accrued 706 hours of Beech 1900D time.

Investigators discovered that the airplane had undergone a maintenance check overnight, beginning on January 6. They determined that when the airplane went in for maintenance, the elevator control system was properly rigged to permit full elevator travel in the downward direction. During the maintenance check, however, the elevator control system was incorrectly rigged. This restricted the airplane's elevator travel to seven degrees AND or about half of what it should have been. Investigators found that a mechanic who had been receiving on-the-job training incorrectly adjusted the elevator control system and that rigging procedures weren't followed. The Safety Board concluded that the incorrect rigging wasn't a significant factor on the preceding flights because weight and balance on those flights were well within limits.

The National Transportation Safety Board determined that the probable cause of the accident was the airplane's loss of pitch control during takeoff, which resulted from the incorrect rigging of the elevator control system, compounded by the airplane's aft center of gravity. The Safety Board said the airline's lack of oversight of maintenance work and the FAA's lack of oversight of both the airline's maintenance program and the airline's program for ensuring aircraft weight and balance were among the factors that contributed to the accident.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.