ROBINS AIR FORCE BASE, Ga. — There are times when what you can’t see can be a lifesaver, especially when it comes to ensuring the safety of F-15 pilots.

In November, an extensive crack was discovered during a routine nondestructive inspection of a right F-15 wing spar, the critical component that attaches to the aircraft.

An initial ultrasound inspection of the spar included a particularly challenging location to inspect. Something caught the eye, or rather ear, of NDI work leader Helen Mulvaney, who became suspicious of the accuracy of the ultrasound.

While a visible crack could be seen once the wing was taken apart, a second inspection method was performed using a bolt hole eddy current probe for a more accurate look.

With the bolt hole inspection, the probe is looking for an air gap, or crack. If there’s no indication of one, there’s no crack. 

In this case, the crack was about a half inch on each side of the identified hole.

“Lo and behold, it was a pretty-good-sized crack that went from one side of the hole, across and through it, and out the other side up the web,” she said. “It was definitely crucial that we be 100 percent since this was for an aircraft returning to Nellis Air Force Base, Nevada.” 

That particular spar is no longer in service because it couldn’t be repaired.

Following the direction of engineers from the System Program Office, the 402nd Commodities Maintenance Group was tasked to inspect other C/D model F-15s at Robins. 

As of December, eight wings had been inspected, and three repaired at Robins. There are more than 100 F-15s in the fleet that are potentially affected, according to Ben Stuart with the 573rd CMXG.

Once defects are found, machinists — including Josh Bryant and Levi Wilcox — work diligently to remove cracks. 

“With cracks being found on the bottom side of the wing, there’s a lot of stress put on it,” said Bryant.

Tools are used to create precise-sized holes in the spar, which is made out of titanium. The process is slow and tedious and performed with extreme care since titanium is tough to drill through.

Brig. Gen. Eric Fick, the Air Force Life Cycle Management Center’s program executive officer for Fighters and Bombers, paid a visit to Robins in early December for an up-close look at some of the work being done on F-15s.

“I appreciate CMXG’s diligence in helping identify this issue,” he said. “This is a great demonstration of the cooperative efforts between the Air Force Life Cycle Management Center and the Air Force Sustainment Center in developing a way for the field to check for this hard-to-find phenomena. We’re working collaboratively to identify the extent of the issue and posture ourselves to meet it head-on.”