Managing Aging Aircraft

By Jeff Guzzetti

It was the most dramatic aircraft accident video clip I have ever seen, and I've seen plenty during my 15-plus years as an air safety investigator. As I watched the nightly news, the video showed both wings fold upward and separate from the center section of the military-surplus Lockheed C-130 that had just completed a fire retardant drop in Walker, California. The wingless, cigar-shaped fuselage then continued on its deadly trajectory, careening into the mountainside, bursting into flames, and killing the three-person crew (see photo).

After an exhaustive investigation (NTSB Case Number LAX02GA201), the National Transportation Safety Board determined that the probable cause was "the inflight failure of the right wing due to fatigue cracking in the center wing lower skin and underlying structural members." More importantly, the NTSB also ruled that a factor contributing to the accident was "inadequate maintenance procedures to detect fatigue cracking."

As a result of this accident and two others involving military-surplus firefighting aircraft, the Board issued several recommendations to the U.S. Forest Service to "develop maintenance and inspection programs for aircraft that are used in firefighting operations..." that take into account things such as the airplane's original design requirements, intended mission, operational life, and a detailed engineering evaluation to predict and prevent fatigue separations. The Board also issued a recommendation to "hire personnel with ... maintenance expertise to conduct appropriate oversight..." to ensure that the new maintenance requirements are met.

The story doesn't stop there. Since the Walker accident, numerous deadly inflight breakups involving other military-surplus aircraft have occurred. Most recently there was the Chalk's Ocean Airways accident in Miami on December 19, 2005 (NTSB Case number DCA06MA010) in which the right wing broke off of a turbine Mallard commercial seaplane during climbout, killing all 20 people on board (see related story page 22). All of these accidents involved metal fatigue failures. Some maintenance programs may not require adequate inspection of the areas most susceptible to fatigue damage. In some cases, the manufacturer may not have considered fatigue life or damage tolerance in the design of the aircraft structure. But in most instances, current nondestructive inspection methods (for example, dye penetrant, eddy current, X-ray, etc.) will detect fatigue cracking before it reaches a critical level.

Regional NTSB investigators are currently investigating pure civilian general aviation (GA) aircraft that are having problems associated with "old age." Investigators are analyzing fatigue cracks on a wing spar in several twin-engine Cessna 402s, a plastic control yoke that failed during takeoff in a Cessna 205, and deteriorated seat restraints in a fatal F-19 Taylorcraft accident. All of these airplanes were well over 30 years old. Is it possible that the military surplus aircraft accidents are leading indicators of a burgeoning problem with aging GA aircraft?

When most general aviation aircraft were designed and built in the 1950s, it was never imagined that they would last beyond 30, 40, or 50 years. According to the General Aviation Manufacturers Association (GAMA), the average age of the piston-powered general aviation fleet is about 35 years old. FAA survey data indicate that more than 40,000 GA aircraft flying today are more than 40 years old!

What can maintenance managers and technicians do to mitigate potential problems with aging aircraft? For starters, they can ensure that all required maintenance and inspection items that exist for the airframe are scrupulously followed. They can also ensure that close attention is given to structural inspections in order to pick up indicators of fatigue damage. Aging airplanes are susceptible to fatigue damage even when operated well within the original load envelope as designed by the manufacturer. This susceptibility increases when the airplanes are operated near the maximum design limit load envelope.

To this day, I use the dramatic video clip of the Walker C-130 inflight breakup to kick off the two-week Basic Aviation Accident Investigation Course that is taught every year to new investigators at the NTSB Academy in Ashburn, Virginia. The investigation and the recommendations demonstrate to the students that accident prevention is why we undertake our grim task. In my business, to see how an airplane "dies" we first must determine how it lived. That's where maintenance managers and technicians enter the story. If an aging airplane is not adequately maintained and inspected, then the airplane, and the people it carries, will die. It's that simple.

Jeff Guzzetti is deputy director for regional operations, National Transportation Safety Board Office of Aviation Safety.