In this issue we unearth the challenges of both isolating the root causes and conceiving solutions for no fault found (NFF) (see story), a complex problem affecting operators, maintenance facilities and original equipment manufacturers (OEMs), alike. NFF and its main contributor, the intermittent failure, cause unwanted expense, even hazards. For example, pilot response to an intermittent malfunction of a position indicator was a suspected contributor to the fatal 1992 crash in Panama of COPA Airlines' Flight 201, according to a report penned by Brent Sorensen, president of Universal Synaptics. In what may prove to be one of the costliest intermittent failures ever, an apparently malfunctioning hydrogen fuel sensor postponed the launch of the Space Shuttle Discovery on July 14.
Definitive statistics regarding NFF are difficult to nail down. Different sources will give different ratios of NFFs to hard failures. Nevertheless, the problem represents at least a costly nuisance that has many members of the aviation community investing appreciable manpower and money to resolve.
An example of an airframe OEM's quest to reduce NFFs is Dassault Falcon in Teterboro, N.J. For several years this U.S. division of the French aircraft manufacturer has been tabulating the NFFs reported on its customers' business jets. The result is not only a greater understanding of the NFF problem, but also a course of action that has reduced the company's NFF reports significantly, according to Gerry Goguen, Dassault Falcon's senior vice president-customer service.
Much of what the study discovered mirrors what is mentioned in our coverage (page 22). However, in addition, it found that just 15 percent of the NFF reports come from operators of older aircraft, while the remaining reports comes from operators of newer aircraft. The protection of the newer aircraft's warranty would explain why many operators would more freely submit suspicious components for test and repair. But Goguen suggests other factors, claiming that modern bizjets are more complex and that the operator's support staff often "doesn't understand the troubleshooting process yet."
Older aircraft have their own obstacles to mitigating NFF. "Cost of maintenance becomes a driver," Goguen explains, "and too often the lesser trained mechanics are assigned to the older aircraft."
He adds that, according to his company's study, "the parts most prone to no fault found are computers and control systems that have multiple inputs." In that light he says the older aircraft can aggravate the NFF problem. They "are less integrated, [so] the computer takes inputs from a variety of components; and all those parts have gone through an evolution, [so] the test procedure has to be adjusted to a configuration that didn't exist when [the computer and connecting parts] first came out."
The Dassault Falcon study also tracks the source of NFF reports and uses that data to alleviate the problem. How so? "We try to make arrangements with two repair agents for each [type of] part," says Goguen. "If one has more no fault founds than the other, we have our audit team visit them to identify what may be wrong with their testing procedures." At the same time, the company also tracks operator deliveries of parts for test and repair. If one operator sends in a type of part that results in NFFs more often than other operators using the same part, "then we visit that operator to examine his method of troubleshooting," says Goguen. Using its tracking processes and its visits to repair facilities and operators, Dassault Falcon has managed to reduce NFFs by up to 30 percent.
"I think many operators believe a box has some inherent evil in it, and you can't trust it," says Goguen. "But we've learned that a majority of the no fault founds have a logical explanation."
Despite the diagnostics and built-in test equipment in today's aircraft, no fault found will doubtlessly continue to vex the aviation industry. But entities affected by the problem can reduce NFFs through thorough analysis and actions taken by companies such as Dassault Falcon. Says Goguen, "The research we conducted is the only way I know to reduce the [NFF] problem."