WASHINGTON — Only about half of the F-35 fighter jets worldwide were ready to fly during an eight-month period in 2018, with the wait for spare parts keeping jets on the ground nearly 30 percent of the time, according to a new report by the U.S. Government Accountability Office.

Over the past several years, the Defense Department sought to improve mission-capable rates by making improvements to the way it and F-35 manufacturer Lockheed Martin order, stockpile and repair spare parts. However, GAO’s findings imply the situation may have gotten worse.

The GAO’s report, released April 25, investigated how spare parts shortages impacted F-35 availability and mission-capable rates in 2018, with most data gathered between a May and November sustainment contract period.

“In 2017, we reported that DOD was experiencing sustainment challenges that were reducing warfighter readiness, including delays of 6 years in standing up repair capabilities for F-35 parts at its depots and significant spare parts shortages that were preventing the F-35 fleet from flying about 20 percent of the time,” the report found.

“According to prime contractor data, from May through November 2018, F-35 aircraft across the fleet were unable to fly 29.7 percent of the time due to spare parts shortages,” it said. “Specifically, the F-35 supply chain does not have enough spare parts available to keep aircraft flying enough of the time necessary to meet warfighter requirements.”

That lack of improvement may make it more difficult for the U.S. Air Force, Navy and Marine Corps to hit an 80 percent mission-capable rate by the end of fiscal 2019, as mandated last fall by then-Defense Secretary Jim Mattis.

The military services stopped providing mission-capable rates for aircraft last year, citing operational sensitivities. However, the data put forth by the GAO indicates progress stagnated in the lead-up to Mattis’ order.

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From May to November 2018, mission-capable rates — which measure how many planes possessed by a squadron can perform at least one of its missions — hovered around 50 percent for all versions of the F-35.

But when GAO assessed how many planes were fully mission capable — meaning the ability to fulfill all of their mission sets — all variants were far from meeting the 60 percent target. Only 2 percent of F-35C carrier takeoff and landing versions hit the fully mission-capable mark, with the F-35Bs slightly better at 16 percent and the F-35A at 34 percent.

The GAO is skeptical that the services will hit the 80 percent mission-capable rate goal this year, and it is even more critical of the Defense Department’s plans to fund spares in future years.

The department intends to buy “only enough parts to enable about 80 percent of its aircraft to be mission-capable based on the availability of parts.” However, that planning construct will likely only yield a 70 percent mission-capable rate at best, the GAO said, because it only accounts for the aircraft on the flight line and not jets that are in the depot for longer-term maintenance.

No silver bullet

Like all complicated problems, there is no single solution for the F-35 spare parts shortage, which is driven by a number of factors.

GAO indicated the Defense Department has “a limited capacity” to repair broken parts, creating a backlog of 4,300 parts. Between September and November, it took more than six months to fix parts that should have been repaired in a window of two to three months.

The F-35’s much-maligned Autonomic Logistics Information System, or ALIS, was designed to track parts and automate the process of generating and expediting work orders; however, GAO said the system requires manual workarounds from users to accomplish tasks.

Supply and maintenance personnel cited challenges such as “missing or corrupted electronic spare parts data,” limited automation, and problems caused by ALIS’ subsystems not properly communicating with each other, it said.

As the F-35 is still a relatively new platform, it has taken time for the program to assess which parts have been failing more often than previously estimated — but that is an area where the Defense Department is making progress, the GAO stated.

“DOD has identified specific parts shortages that are causing the greatest aircraft capability degradation, and it is developing short-term and long-term mitigation strategies to increase the quantity and reliability of these parts,” the report said.

One such component is a coating used on the F-35’s canopy to maintain stealth characteristics, which has been found to peel off at an unexpected rate, creating a heightened demand for canopies.

“To address these challenges, the program is looking for additional manufacturing sources for the canopy and is considering design changes,” the GAO stated.

But — somewhat paradoxically — the F-35 has been flying long enough that there are significant parts differences between the first jets that rolled off the production line to the most recently manufactured planes. The GAO found “at least 39 different part combinations across the fleet” on top of variations in software.

“According to the program office, DOD spent more than $15 billion to purchase F-35 aircraft from the earliest lots of production, specifically lots 2 through 5 … but it faces challenges in providing enough spare parts for these aircraft,” the report stated.

One problem — the cannibalization of F-35 aircraft for parts — is partially user-inflicted.

“From May through November 2018, F-35 squadrons cannibalized (that is, took) parts from other aircraft at rates that were more than six times greater than the services’ objective,” the GAO stated. “These high rates of cannibalization mask even greater parts shortages, because personnel at F-35 squadrons are pulling parts off of other aircraft that are already unable to fly instead of waiting for new parts to be delivered through the supply chain.”

During an interview this February, Lt. Col. Toby Walker, deputy commander of the 33rd Maintenance Group, told Defense News that F-35 maintainers at Eglin Air Force Base, Florida, had stopped pulling parts off a cannibalized F-35 and had seen some improvements to mission-capable rates as a result.

“We’re not continually moving parts from one aircraft to another. We’re relying on the program to provide our parts,” he said. “It was a very strategic plan to do that to increase aircraft availability by not sitting an aircraft down.”

In a statement, Lockheed Martin said it took key steps to improve parts availability, such as transitioning some suppliers to performance-based logistics contracts that incentivize companies to meet certain targets, as well as “master repair agreements” that will allow other suppliers to make longer-term investments in their production capability.

“These actions are beginning to deliver results and we’re forecasting additional improvement. Newer production aircraft are averaging greater than 60 percent mission capable rates, with some operational squadrons consistently at 70 percent,” the company said.