The fleet of F-35 Joint Strike Fighters flying in the critical operational testing phase is struggling to stay airborne, which could delay the troubled program’s great leap forward into mass production.

As I recently reported for the Project on Government Oversight (POGO), a document from the program’s test force shows that the fleet’s test aircraft, housed at California’s Edwards Air Force Base, have netted an average 11 percent “fully mission capable rate”—the key measure of how often an aircraft can perform all of its assigned missions—since the process began last December.

To put this into context, the Pentagon’s former operational testing director, Michael Gilmore, has said the fleet needs an 80 percent availability rate to successfully complete the combat-testing phase.

The F-35, by the way, is already the most expensive weapons system in history. As of March, its acquisition price tag was $400 billion. However, the cost of operating and maintaining the fleet over the next several decades stands at an estimated $1.45 trillion.

The 17-year-old program reached an important milestone when, after many delays, officials started the Initial Operational Test and Evaluation (IOT&E) process on December 5, 2018. This is the phase in which the completed product is put through its paces in realistic combat scenarios to determine whether it can fulfill its intended role and is suitable for pilots’ use.

This is supposed to take place after the former design phase. But because the F-35 program hasn’t actually finished the design process, the program effectively created extra obstacles to successful completion of this legally required testing phase. That the test fleet struggles even to get off the ground only compounds these challenges.

The 23-aircraft fleet had a bad start, with a fully mission-capable rate of just 11.5 percent in December, and the situation has only worsened since. The “IOT&E Aircraft Readiness Rates” chart obtained by POGO shows that the fleet’s June 2019 fully mission capable rate was just 8.7 percent. Sure, it was an improvement over May—because then it was an even more dire 4.7 percent.

The chart shows three categories: fully mission capable, “partially mission capable,” and “non-mission capable.” Partially mission capable (commonly called “mission capable”) aircraft can perform at least one of their missions; non-mission capable is self-explanatory. Fully mission capable status is an especially crucial metric of readiness for multi-mission programs like the F-35.

Major defense acquisition programs are legally required to complete operational testing, with the results reported to the secretary of defense and Congress by the operational testing director before progressing to full-rate production.

The clock is ticking. A full-rate production decision is expected in October. It’s hard to imagine that the program will be able to finish operational testing by the deadline.

Careful readers will be surprised to learn that the operational test fleet is actually performing worse than the F-35s in the active Air Force, Marine Corps, and Navy squadrons. The test fleet is made up of 23 F-35s equipped with specialized instruments to record flight and combat data for later analysis to determine the program’s overall effectiveness. According to the latest available figures, the F-35s in the active forces managed a fully mission capable rate of only 27 percent. Nothing to crow about either.

Meanwhile, as the Air Force Times recently reported, the Air Force is contending with a readiness crisis. Data for 2012 through 2018 shows declining mission-capable rates across all aircraft programs—encompassing 5,400 aircraft—from an overall average mission capable rate of 77.9 percent seven years ago to 69.97 last year.

Responding to the sorry state of aircraft readiness, last September then-secretary of defense James Mattis gave the services a year to get to an 80 percent mission capable rate. The Air Force may need a miracle.

The Air Force’s struggles notwithstanding, 80 percent mission capable throughout all programs is a pretty modest goal—though a worthy one. Mattis’s directive focused on mission capable rates, rather than fully mission capable rates, a much more important measure of combat-effectiveness.

A spokesman told the Air Force Times that the low readiness rates are mostly due to the fleet’s age. All you have to do is glance at the numbers to see that’s just not true. Next to the legacy aircraft they’re meant to replace, newer aircraft like the F-22 and F-35 don’t look so hot. While the F-22’s average mission capable rate last year was 51.74 percent, the older F-15E’s was 71.16 percent. The F-35A’s average mission capable rate was 49.55 percent, about 16 percent lower than the F-16D’s and nearly 23 percent lower than the A-10C’s.

Colonel Bill Maxwell, head of the Air Force’s maintenance division, also downplayed concerns to the Air Force Times, calling the overall mission capable rate just a “snapshot in time.”

The F-35 operational test fleet readiness chart that POGO published offers six months’ worth of data for the most expensive weapon system in history, and shows dependably low readiness in the legally required combat-testing phase.

Now it’s up to Robert Behler, the current director of operational testing.

He could give in to pressure to keep to the Pentagon’s arbitrary schedule, call a halt to the tests in October, and allow the program to move to full-rate production without completing the testing plan. But that would be a mistake. At this point, there’s far more at stake: the public’s trust and the troops’ trust, not just in the F-35 but also the integrity of the testing process and the business of acquiring the right tools for the military.

If there is to be any hope of salvaging something from the nightmare that has become the F-35, the design needs to be adequately tested. Only then will the full extent of the program’s shortcomings be revealed and fixes implemented to prevent more taxpayer money from being wasted on flawed aircraft.

Dan Grazier is the Jack Shanahan Military Fellow at the Project on Government Oversight. He is a former Marine Corps captain who served tours of duty in Iraq and Afghanistan during the war on terror. His various assignments in uniform included tours with 2nd Tank Battalion in Camp Lejeune, North Carolina, and 1st Tank Battalion in Twentynine Palms, California.