While inspecting the F-35C in late October, a crack was found in one of its 13 wing spars, Joe DellaVedova told IHS Jane’s. Government and prime contractor engineering teams are formulating a solution, he added.

“Initial estimates indicate a modification of approximately a half a pound to the aircraft will fix it,” said DellaVedova. “Modifications to planes flying today will be incorporated to ensure full life operation.”

The issue is not expected to affect flying operations for any of the three variants, nor will it alter the US Navy’s ability to meet its planned Initial Operating Capability (IOC) for the C-model in August 2018, according to the JPO.

The cracks were found while inspecting durability testing, in which aircraft is deliberately stressed to its structural limits by applying cyclic loads to the airframe to simulate operational flying in order to identify weaknesses and potential corrective actions, IHS Jane’s reports

It is not yet known how much the fix will cost, but it will add to the F-35 program’s overall cost, which has ballooned to more than $1 trillion, making it the most expensive weapons program in the Pentagon’s history.

The cracks are just the latest in a long line of flaws in the program, which has been plagued by systems malfunctions, schedule delays and cost overruns.

The F-35C variant is distinguished by its larger wings and more robust landing gear, designed for catapult launches and arrestments aboard naval aircraft carriers, and its wingtips fold to allow for easier storage aboard a carrier, IHS Jane’s reports.