Former NTSB and FAA investigator Jeff Guzzetti explains how shortcutting the procedure to rig the elevators of a commuter plane led to a tragic accident shortly after takeoff.
As a former aircraft accident investigator, I can attest to the fact that the incorrect rigging of flight controls has led to numerous in-flight emergencies, accidents, and even deaths. Maintenance personnel who serviced or checked the controls did not recognize that the surfaces were moving in the wrong direction. In some cases, the mechanics who performed this work were highly experienced. Anyone can make mistakes, but these mistakes usually lead to tragic circumstances.
Perhaps the most notorious of these types of events occurred on January 8, 2003, when Air Midwest — doing business as US Airways Express flight 5481 — crashed shortly after takeoff from Charlotte, North Carolina. The two pilots and all 19 passengers on board the Beech 1900D turboprop commuter were killed. The National Transportation Safety Board (NTSB) investigation into this crash was intense, complex and comprehensive, and it yielded many lessons learned for airline maintenance professionals.
At the time of the accident, I had recently been promoted out of the NTSB’s Major Investigation Division, so I missed the opportunity to lead the “go-team” in Charlotte. However, in my new role as the head of all NTSB field offices, I closely monitored the investigation and supervised the investigation of a second Beech 1900D mis-rigging event that occurred nine months later.
The Investigation
The NTSB arrived at the Charlotte crash site a few hours after the accident, and their first order of business was to retrieve the “black boxes.” An initial audition of the cockpit voice recorder (CVR) revealed trouble as soon as the landing gear was raised upon liftoff. For the next 26 seconds, the airplane pitched up, stalled, and descended into the side of a hangar, igniting a massive fireball (see graphics 1 and 2).
The final word recorded on the CVR was from someone in the passenger cabin who yelled “Daddy” — a stark and emotional indication of the potential consequences of improper maintenance.
Information from the flight data recorder (FDR) showed that the airplane was rotating nose-up after takeoff, even though the flight crew was pushing the control column fully forward and trimming the airplane in the nose-down direction. This prompted investigators to focus on the pitch control system of the Beech 1900D, which consisted of cables, pulleys and bellcranks connecting the cockpit control columns at the front of the airplane to the elevator surfaces at its tail (see graphic 3).
The pitch control system also included two turnbuckles that allowed mechanics to adjust the position and cable tension of the system (see graphic 4). Examination of the turnbuckles as found in the wreckage revealed that the nose-down turnbuckle, which measured 7.30 inches in length, was extended 1.76 inches more than the nose-up turnbuckle, which measured 5.54 inches in length (see graphics 5). By quickly conducting a survey of its fleet of 42 Beech 1900D airplanes, the airline discovered that these measurements were not normal. The survey results indicated that the nose-down turnbuckle was extended, on average, only 0.04 inch less than the nose-up turnbuckle, rather than the 1.76-inch difference noted in the wreckage.
Investigators quickly learned that the airplane had undergone a “Detail Six” or D6 maintenance check two days prior to the accident at Air Midwest’s West Virginia maintenance station (see graphics 6). FDR data, ground test results, and aerodynamic analysis showed that, before the D6 check, the airplane’s full range of downward elevator travel was available. However, after the D6 check, the downward elevator travel was limited to about seven degrees rather than the 14-15 degrees specified in the Beech 1900D Airliner Maintenance Manual (AMM).
Part of the D6 check involved checking the tension of the elevator control system cables and adjusting the tension if necessary. The mechanic who performed this work had not previously performed it on a Beech 1900D. As a result, he was receiving on-the-job training (OJT) from a quality assurance (QA) inspector for the tasks associated with that part of the D6 check.
The mechanic determined that the airplane’s cables needed to be adjusted because their average tension was too low. He stated that he adjusted the cables and performed some, but not all, of the steps of the elevator rigging procedure. However, whenever cable tension adjustments are made, the entire elevator control system rigging procedure needs to be performed — not just those steps that apply to cable tensioning.
While NTSB could not precisely determine the changes that were made to the elevator control system during the D6 check to restrict the elevator travel, they discovered during ground testing a scenario that was consistent with FDR data from the accident airplane and the physical measurements of the turnbuckles. Specifically, when the rig pin for the aft bellcrank was not removed and the cable tension was released, and then the rig pin for the forward bellcrank was installed aft of the bellcrank arm, adjustments to the turnbuckles resulted in a nose-up turnbuckle length of 5.12 inches and a nose-down turnbuckle length of 7.70 inches. After the aft rig pin was removed, the test airplane’s elevator moved to 7.7 deg. nose-down.
Skipped Steps and Inadequate OJT
Five of the six mechanics who were on duty on the night of the D6 check had worked at the West Virginia facility for less than eight weeks, and none of them had completed training for the D6 check. The mechanic assigned by the foreman to perform the elevator control cable check was selected for the task because he had previously accomplished flight control rigging work on another type of airplane (DeHavilland DHC-8). The QA inspector, who was providing the mechanic’s OJT, stated that he did not think he needed to closely supervise the mechanic because of his previous flight control rigging experience.
The mechanic stated that, before he inspected the elevator control system, the foreman helped him locate the access panel for the forward bellcrank rig pin and the elevator cable turnbuckles. The mechanic also stated that he and the QA inspector discussed the low cable tensions, the need to adjust the tensions, and the steps that could be skipped. The QA inspector then left to attend to other duties, and another mechanic held the turnbuckles while he adjusted them. The QA inspector returned after the rigging work was completed to observe the final check of the elevator control system.
The QA inspector stated that, after he verified that the forward bellcrank rig pin had been inserted, he left the mechanic unsupervised during the elevator control cable inspections and turnbuckle adjustments. The QA inspector indicated that he had to provide OJT to another mechanic and also perform a borescope inspection on an engine.
The Beech 1900D elevator control system rigging procedure did not include provisions for adjusting cable tension as an isolated task. However, the mechanic decided to adjust the cables as an isolated task and, as a result, did not follow each step included in the rigging procedure. The QA inspector was aware that the mechanic was selectively performing steps from the rigging procedure and that he was only adjusting cable tension. In fact, the inspector stated that he did not think the manufacturer intended for mechanics to follow the entire rigging procedure and that the entire procedure had not been followed when past cable tension adjustments were made.
The NTSB opined that the insufficient training and supervision resulted in the mechanic making mistakes that led to the incorrect rigging and the restricted downward elevator travel. If the QA inspector had provided better training and supervision, the likelihood of such errors would have been minimized.
Another Beech 1900D Mis-rigging
Then, on October 16 of that same year, another Beech 1900D was found to have mis-rigged elevator controls. This time, the airplane was operated by CommutAir as Continental Connection flight 8718. As the airplane accelerated for takeoff from Albany, New York, the captain noted that the elevator control was jammed, prompting him to abort the takeoff. Fortunately, no one was hurt, but the Major Investigations Division asked that I dispatch one of my field office investigators to initiate an incident investigation, given the limelight of the fatal Charlotte accident nine months prior.
Examination of the incident airplane revealed that when the elevator trim wheel in the cockpit was positioned to neutral, the elevator trim was actually in the full nose-down position. The incident flight was the first flight after maintenance the day before, in which the elevator trim wheel was removed and reinstalled. The NTSB discovered that part of the work performed on the airplane included removal and replacement of a throttle pin. To accomplish that procedure, the maintenance technician had removed the elevator trim wheel. However, he did not index the elevator trim wheel before removing it, and reinstalled it incorrectly.
To make matters worse, neither the maintenance technician nor the QA inspector performed a functional check of the elevator trim system following the maintenance. Also, NTSB was shocked to learn that AAM had no published procedure regarding the removal and reinstallation of the elevator trim wheel.
Causes, Factors, and Lessons Learned
The NTSB determined the probable cause of the Flight 5481 disaster in Charlotte to be the airplane’s loss of pitch control during takeoff that resulted from the incorrect rigging of the elevator system, compounded by the airplane’s aft center of gravity, which was substantially aft of the certified aft limit. The NTSB also cited numerous “contributing factors,” such as the airline’s lack of oversight of the work being performed at the West Virginia maintenance station, and its inadequate maintenance procedures and documentation. They also cited the QA inspector’s failure to detect the incorrect rigging of the elevator control system, and the FAA’s lack of oversight of the airline’s maintenance program and its weight and balance program. The NTSB issued 14 recommendations to the FAA related to air carrier maintenance programs, including one to prohibit inspectors from performing required inspection item inspections on any maintenance task for which the inspector provided on-the-job training to the mechanic who accomplished the task.
The legacy of Flight 5481 is its clarion call to all maintenance personnel to prevent mis-rigging accidents by heeding the following items:
• Become familiar with the normal directional movement of the controls and surfaces before disassembling the systems. It is easier to recognize “abnormal” if you are familiar with what “normal” looks like.
• Carefully follow manufacturers’ instructions to ensure that the work is completed as specified. Always refer to up-to-date instructions and manuals — including airworthiness directives — when performing a task.
• Be aware that some maintenance information, especially for older airplanes, may be nonspecific. Ask questions of another qualified person if something is unfamiliar.
• Remember that well-meaning, motivated, experienced technicians can make mistakes: fatigue, distraction, stress, complacency, and pressure to get the job done are some common factors that can lead to human errors. Learn about and adhere to sound risk management practices to help prevent common errors.
• Ensure that the aircraft owner or pilot is thoroughly briefed about the work that has been performed. This may prompt them to thoroughly check the system during preflight or help them successfully troubleshoot if an in-flight problem occurs.