WASHINGTON — Software glitches have plagued the F-35 in recent months, but operators said they noticed a marked improvement during a June deployment where the aircraft did not experience any shutdowns.

The F-35 joint program office's top official disclosed in April that the fighter jet was struggling with problems associated with the 3i software planned for use when the Air Force fields the planes later this year. Pilots reported that they had trouble booting up their jets, and would have to restart key systems on the plane every three to four hours after sensors shut off without warning.

The program office implemented a fix the following month, and pilots and maintainers who operated the plane during the June deployment at Mountain Home Air Force Base, Idaho, said software bugs no longer seemed to be an issue.

"We cleared 88 of 88 sorties, and we were on time for 100 percent of those sorties for the large force exercises," Maj. Brad Matherne, an F-35A pilot from the 34th Fighter Squadron, told reporters during a June 21 conference call. "We had zero losses due to any software stability issues that were previously out there."

Seven F-35As and a total of 160 pilots, maintainers and other personnel from Hill Air Force Base, Utah, were sent to Mountain Home ahead of the F-35A's initial operational capability, which could come as early as August. The deployment, which took place June 6-17, proved that the aircraft could successfully operate away from its home base against a variety of threats, said Col. David Lyons, commander 388th Fighter Wing and an F-35A pilot.

For the deployment, jets were outfitted with the latest version of the software, 3ib6.21, Matherne said. He said that no shutdowns occurred on the ground or in flight due to software glitches.

"To my knowledge, we did not have any degradations due to software instability," he said. "From a mission systems and tactical employment, we met all of our tactical objectives, which would have been very difficult if that software was an issue, which it was not."

Spare F-35s were used twice due to minor hardware problems that kept jets grounded during takeoff, said Capt. Richard Palz, officer in charge of the 34th Aircraft Maintenance Unit. In one incident, an internal battery failed and had to be removed and replaced. During the second event, the plane's initial navigation system failed, necessitating maintenance.

Both aircraft were returned to service after undergoing repairs and exhibited no additional issues, he said.

Having to move to a spare aircraft is not unusual, even during normal operations, Lyons said.

"We were able to make on-time takeoffs to be a part of the mission and do what we needed to do," he said. "Those are minor problems that you experience with any sort of aviation operation, and I was very, very impressed with the airplane from a reliability and stability perspective," he said.

Col. David Smith, commander of 419th Fighter Wing and currently an F-16 pilot, noted the two F-35 ground aborts are actually an improvement when compared to the failure rates of the F-16 and other 4th-generation aircraft.

The software's performance showed a marked improvement compared to a previous deployment to Mountain Home. During an exercise last February, F-35A aircraft from Edwards Air Force Base, Calif., prepared to make a rapid launch, but only one of six aircraft was able to successfully take off. In written testimony to the Senate Armed Services Committee in May, Michael Gilmore, the Pentagon's lead weapon's tester, characterized the system shut down and restarts as "a symptom of immature systems and software."

Valerie Insinna is Defense News' air warfare reporter. She previously worked the Navy/congressional beats for Defense Daily, which followed almost three years as a staff writer for National Defense Magazine. Prior to that, she worked as an editorial assistant for the Tokyo Shimbun’s Washington bureau.