Close Call: An Aircraft Maintenance Human Factors Tale

Flying Safety, August, 2001

Aviation Safety Maintainer, Issue 1/2001

(Overworked. Undermanned. Rotating shifts. Low experience levels. High Ops Tempo. Deployed location. Inadequate/incomplete tech data. Miscommunication. Someone who didn't perform the corrective action signs the "Corrected By" block in the forms. Any of this sound familiar? We urge you to read, heed and act-by applying ORM--if one or more of the preceding elements exist in your workcenter. The following narrative, taken from Civil Aviation, Transport Canada's newsletter "Aviation Safety Maintainer," provides a chilling account of how these factors all set the stage for a nearcatastrophic mishap that would have destroyed an aircraft and killed several people if not for the skill of the aircrew and a measure of luck. Remember: Every accident is preceded by a series of events that link up to form a "mishap chain." Changing just one of those events means you can break the chain and prevent the mishap from ever occurring. And every single one of us has the power to break that chain--use it. If this tale doesn't get your attention, nothing will. Ed.)

The pilots of the Convair 580 cargo flight were confronted with a severe nose-up pitch tendency immediately after takeoff. The aircraft had been loaded, and documentation, including the weight and balance sheet, maintenance records, and flight plan, was checked by the flight crew prior to boarding the aircraft. It was noted by the flight crew that considerable maintenance work had been done to the aircraft and that some of the work had involved the elevator and elevator trim. Despite this information and the fact that the aircraft was nearing an uncontrolled condition, the flight crew diagnosed the problem as a weight shift. The pressure of hands and feet on the control column by both pilots was barely enough to get the nose down for a safe landing--an extremely hazardous situation.

Back on the ground it was determined that the (cargo) centre of gravity was within limits and not related to the actual problem. It was also discovered that the elevator trim tab was in the full nose-up position and moved in the opposite direction to the trim control wheel and to the trim indicator in the cockpit. A number of years ago, the Canadian Forces had several incidents resulting from inattention and carelessness during maintenance of flight controls on Cosmopolitan aircraft, the military version of the Convair 580.

At this point, a host of human factors come to light that I will list from the report, as follows:

1. The maintenance base was remote from the parent company and had operated for three years, during which time the company experienced rapid expansion and an increased workload without an increase in staff.

2. The expansion required new staff, but the company found that there were few licensed AMEs available, so they hired technicians in training.

3. There are no regulations regarding the ratio of licensed engineers to technicians in a company, so over half of the employees were under supervision.

4. To fulfill the requirement for 24-hr. servicing coverage, the crews worked rotating 10-hr. shifts.

5. The maintenance work involved in this occurrence took place on the second and third nights of a four-night work cycle. The crew had been working the night shift for a period of five weeks. They were on days, off for three days, and then started back on the night shift schedule. This was their last night shift before returning to the day shift cycle.

6. The occurrence aircraft was a Convair 440 that had been converted by a supplemental-type certificate to a Convair 580. This was an older generation aircraft for which the company had not yet developed a complete set of work cards.

7. The aircraft was acquired at the maintenance base five days before the occurrence for the completion of numerous maintenance tasks.

8. As a result of non-destructive testing (NDT), corrosion that required the removal of the elevator and stabilizer was found. These were removed as a single unit, which meant that only the elevator connection bolts, the stabilizer connection bolts, and the elevator trim cables needed to be disconnected. The elevator trim cables were not marked when they were disassembled; it is not a procedure specified in the maintenance manual, but is one that is considered good practice in the industry. The horizontal stabilizer and elevator were repaired as necessary and reinstalled.

9. The maintenance crew that removed the stabilizer assembly was not available when it was time to reinstall it, so the job was finished by another crew.

10. There were not enough qualified engineers, so the crew chief showed the technicians how to install the stabilizer and hook up the elevator trim cables.

11. The crew chief selected the cables, and the technicians installed the turnbuckles. The crew chief then provided them with the appropriate information on bolt torque and cable tension and left them to complete the job. It was his view that he was helping them with the routine but important task of installing and inspecting the stabilizer, elevator, and elevator trim systems.