WASHINGTON — Amid the cold winds and snow, a ghost is haunting F-35 jets in the far north, and it’s causing pilots to divert flights and land immediately.

The good news: This ghost is digital.

In early 2018, multiple F-35A flights out of Eielson Air Force Base in Alaska were disrupted when pilots received warnings that a key battery in the plane was failing mid-flight. The pilots were forced to land as quickly as possible and switch out the battery, wiping out flying hours and raising costs for maintenance — and raising the fear that in an emergency, the U.S. would be unable to scramble its high-end fighter.

After studying the issue, the Air Force discovered the problem was a result of extreme cold entering the plane when the doors to the jet’s nose landing gear were open, setting off alarm bells, according to “for official use only” documents exclusively obtained by Defense News.

The cold would enter the plane and overwhelm the battery heater blanket, which is installed to keep a 28-volt battery running at peak condition. The battery would not shut down, but because of the cold, the blanket could not heat the battery as quickly as intended, triggering warning lights in the cockpit that the battery was going to fail.

Although the plane is equipped with another 270-volt battery that serves as the main power, the redundant system is considered vital for backup power in case of a glitch, and safety protocols dictated that the pilots had to immediately land the plane, even if the battery ultimately would have heated up.

The pilots then had to go to “cold iron” to reset, or turning the engine and restarting the whole plane.

The battery challenge “critically restricts the combat readiness” of the Air Force, the document warned, adding that it is “expected to prevent launch of mission[s] on very cold days.” It also leads to unnecessary maintenance performed on the batteries.

The issue is particularly important for the F-35, which is expected to spend a lot of time in the coldest parts of the globe. In addition to partner nations like Norway and Denmark, who plan to use the fifth-generation fighters beyond the Arctic Circle, the U.S. Air Force has plans for the F-35 to be the core of its Arctic operations.

In a January op-ed for Defense News, U.S. Air Force Chief of Staff Gen. David Goldfein and then-Secretary of the Air Force Heather Wilson wrote that the Arctic represents both a northern approach to the United States as well as a critical location for "projecting American power, its geo-strategic significance is difficult to overstate. Key defense assets dot the landscape. ... One way to view the region’s growing importance: By 2022, Alaska will be home to more advanced fighter jets than any place on Earth.”

However, Rebecca Grant of IRIS Independent Research says there is “no way” the Air Force would let this issue scuttle missions if needed.

“The USAF is not going to accept ‘no-go’ for cold weather launches,” she said. “The F-22 and plenty of other aircraft have flown out of Alaska just fine for decades. The F-35 should have had all that sorted out in the climatic lab.”

Cold as ice

Indeed, the F-35 Joint Program Office seems to have found a solution, one that lets the flights go on, even if it is more of a workaround than a full solution.

One small step involves a recommendation that when the jet flies in particularly cold conditions — something fairly easy to predict, thanks to modern weather stations — the heater blanket be activated earlier than normal.

The bigger step involves changing how the alert system recognizes a failure, through a software change. Essentially, because the battery ultimately was going to be OK if the warning light had not gone off so easily, the JPO and prime contractor Lockheed Martin agreed to change the levels at which the warning activates.

“Bottom line, it was just saying: ‘Your battery is not good to go,’ ” according to a source familiar with the matter. "And we needed to change the logic so that the battery will be like: ‘Yep, we’re good to go.’ It’s changing the whole heater logic and how the heater works.”

How to do that without creating a situation where the battery really will fail but pilots won’t be alerted to it took “several years” of work and testing from Lockheed engineers, the source added, noting the software fix will be available to retrofit on existing planes later this year, and it will be incorporated into all new planes by 2021.

“That verification work is what typically takes a long time doing things like this, because you can’t just go change stuff because often, if you do it wrong, you could mess it up,” the source said.

Greg Ulmer, Lockheed’s vice president and program manager for the F-35, told Defense News that the issue was “identified during extreme cold weather testing at negative 30 degrees or below at Eielson Air Force Base, Alaska in February 2018. The probability of the issue reoccurring on aircraft in the operational fleet is very low and with minimal impact to safety of flight or operational performance.”

Valerie Insinna in Washington contributed to this report.