Human Errors in Aviation Maintenance

Airline flying is becoming less safe, and maintenance errors are playing an increasing role in the reduced level of operational safety, according to a study directed by professor Gary Eiff at Purdue University's Department of Aviation Technology in Lafayette, IN.

The findings -- that maintenance errors were a contributory factor in far more incidents and accidents than previously thought -- come at a time when financially-strapped operators are contracting out more maintenance to save money, and in a period when federal oversight of repair stations has been found lacking (see AM, May 2006, p. 46).

The Purdue study found that while incidents are trending toward fewer per year, the accident trend is in the opposite direction. The total number of accidents and incidents remains relatively the same, but "the criticality of [the] outcome of such events is becoming more severe."

Eiff and his graduate students, who did the grunt work in the Purdue study, looked at all accidents and incidents in the National Transportation Safety Board (NTSB) database over a 20-year period from 1982 to 2002. The Purdue study focused on scheduled passenger operations; it excluded cargo aircraft, where there are known cases of unairworthy aircraft being returned to flight service, and the study excluded charter operations.

The purpose of the study was to determine if maintenance played a more prominent role in aviation accidents and incidents than previously thought.

The Purdue researchers analyzed roughly 1,300 NTSB records of airline accidents and incidents. The study found that maintenance problems were factors in nearly a third (29 percent) of the events. One of the key assumptions in the study was that mechanical failures were maintenance-related. "While the reports do not directly link these mechanical failures to maintenance, it is reasonable to believe that many result from maintenance shortcomings," the report said.

The study found that maintenance was a contributory factor in more cases than previously thought. For example, a Boeing safety summary attributes only about three percent of crashes to faulty maintenance. The Purdue study suggests that maintenance problems may be some 10 times greater.

A major reason for the difference is that the Boeing data includes only hull losses, whereas the Purdue study included accidents below the severity of hull losses as well as incidents.

Does the Purdue study paint a picture that's closer to reality? Well, the data collection was a straightforward exercise: extracting what the NTSB said and compiling it. Moreover, the Purdue study findings may be consistent with other inquiries. For example, an engine manufacturer found that 50 percent of engine-related turnbacks (return to departure airfield) were caused by installation error.

What is to be done? Eiff argues that both managers and maintainers can do better. "The industry has put a lot of time and effort into increasing compliance with procedures for pilots. We need to do that for mechanics," he maintained. As for the mechanics, he said, "[Some] don't look at the policies and procedures as an error defense, as a way to stay out of trouble. So there's an educational process here."