Monday, June 2, 2003
Air Midwest Crash Links Maintenance And Operations
Regional carriers can expect tighter controls on both maintenance programs and operational weight and balance procedures following hearings on the fatal crash of an Air Midwest Beech 1900D at Charlotte, N.C.
The crash occurred on Jan. 8, two days after the aircraft underwent maintenance, causing the National Transportation Safety Board (NTSB) to focus its investigation on the airline's maintenance procedures. It was also carrying a full load of passengers and baggage, possibly placing it almost 300 pounds over its maximum takeoff weight.
The first officer, Jonathan Gibbs, had calculated the weight at 17,018 pounds, just 102 pounds below the maximum weight of 17,120 pounds. However, based on the physical evidence following the crash, NTSB investigators believe the actual weight was closer to 17,400 pounds, or 280 pounds over maximum gross takeoff weight. Because of the baggage stowed in the rear, the aircraft was tail heavy to the extent that its center of gravity (CG) was slightly more than two inches outside the aft CG limit.
At the time of the accident, the Federal Aviation Administration (FAA) allowed operators to use either actual weights or approved weight averages, based on a 1996 advisory circular. Out of 22 operators of aircraft in the 10- to 19-seat category, 15 use weight averaging, including Air Midwest. Aircraft having less than 10 seats must use actual weights.
Using weight averaging, FAA presumes a mix of 60 percent males and 40 percent females. The Air Midwest flight mix was 84 percent male and 16 percent female. If actual weights had been used for the flight, the aircraft would not have been allowed to take off.
The FAA has now updated its average weight based on a survey conducted after the crash. The average weight for a passenger with carry-on plus one checked bag is about 40 pounds heavier than the figures previously used. Had the Air Midwest pilots used the new, updated figures, the aircraft would have been over the legally allowed takeoff weight.
Because of the weight averaging in use at the time of the accident, the aircraft was legally allowed to take off, yet too heavy for safe flight.
Even with the overweight and the aft CG situation, the aircraft should have been controllable under normal circumstances. However, according to NTSB investigator-in-charge Lorenda Ward, investigation of the crash indicated that the aircraft had lost about two-thirds of its down elevator capability. Ergo, as the aircraft broke ground on takeoff, the overloaded tail caused the nose to rise sharply. Without the full down elevator authority, the pilots were unable to lower the nose in order to recover the aircraft. Although the engines were powerful enough to continue the climb, the high angle of attack caused the wings to stall out, rolling the aircraft over into the fatal crash.
The aircraft went in for a scheduled Detail 6 (or D6) check on the night of Jan. 6 at the Raytheon Aerospace [NTSE: RTN] facility at Huntington, W.Va., under contract to Air Midwest. Part of that D6 check required checking the tension of the pitch control cable.
Although Air Midwest had contract with Raytheon Aerospace for the maintenance, the actual work had been subcontracted to a Florida-based company called Structural Modification and Repair Technicians (SMART). That company is essentially an office without any maintenance facilities, and is not an approved repair station. Nor are its officials licensed airframe and powerplant (A&P) mechanics. They simply hire mechanics and place them in other companies' maintenance facilities.
On the night of the D6 maintenance check on the Air Midwest Beech 1900D, there were seven people at the Raytheon facility - five mechanics, an inspector and a foremen. Six of them were SMART employees and the seventh was a Raytheon employee.
NTSB member John Goglia noted that the five mechanics doing the D6 check had "virtually zero experience on the Beech 1900." The mechanic who did the cable tension check was a recently hired mechanic who was receiving on-the-job training (OJT). The supervisor who was providing the OJT, George States, was also the quality assurance inspector for the night's work. States said during his testimony that he had fully rigged the Beech 1900 elevator control cables only one time before, but had tested and adjusted the cable tension "several times."
Testimony during the hearings indicated that several steps during the adjustment and testing phase were skipped. An elevator control system friction test also was not conducted.
When slack was found in the two elevator control cables, turnbuckles were used to increase the tension. However, it was done in such a way that the turnbuckles had a 1.76-inch difference in length, with one being "adjusted to an abnormal position," NTSB said.
The effect of the improper cable tension was shown on the flight data record (FDR)for flights just before the maintenance work and just after. The FDR showed that during normal cruise prior to maintenance, the aircraft flew with the elevator in about a 4 degrees nose-down position. After the maintenance, the elevator during cruise was in about a 13 degrees nose-down position.
Along with the physical difference in the tension cables, several other problems emerged as part of the NTSB hearings. States essentially did the work, showing the trainee, Brian Zias, how to do it. Zias then signed off on the work and States applied his stamp to the paperwork as the quality assurance inspector. In other words, the two men who did the work also signed off on it and approved it. Adjustment of the control cable is a required inspection item (RII). Any RII work must be inspected by a qualified individual holding RII inspector authority who was not involved in performing the work. State's self-inspection was thus in violation of federal aviation regulations.
The Huntington facility was also understaffed, with under-qualified people. Even before the accident, Air Midwest had expressed concern about the short staffing at the facility. As a result of the accident, Raytheon has added two additional people to the Huntington facility and the maintenance manual has been revised with a new and more specific procedure for rigging and tension adjustment.
(Information in the feature comes from NTSB hearings attended and written on by David Evans, Editor-in-Chief, Air Safety Week, a sister PBI Media publication. Tel: 301-354- 1822, e-mail: firstname.lastname@example.org)