WASHINGTON — The military's top weapons tester has been warning for months that the F-35 will not be ready for its final test phase until 2018 at the earliest. On Tuesday, the Pentagon officially acknowledged the schedule slip.

"We reviewed the status of operational test planning, and there is consensus that that is likely to occur in calendar year 2018 given the realities of the schedule at this time," said Frank Kendall, the Pentagon's top acquisition official, during a Tuesday conference call. "The target was the middle of 2017, but it's clear we're not going to make that."

This slip reflects a six-month delay for initial operational test and evaluation, or IOT&E, the last major period of testing before full-rate production. IOT&E will test the F-35's full combat capability, verifying the jets can fly real, operational missions as intended.

The joint program office's objective to begin IOT&E was August or September 2017, said JPO chief Lt. Gen. Christopher Bogdan, speaking to reporters along with Kendall after the F-35 chief executive officer roundtable in Phoenix. But that start date has slipped to January or February, he said.

The challenge lies with retrofitting all 23 aircraft required for IOT&E with the full 3F software and hardware capability, Bogdan said.

"We believe that in order to get all 23 airplanes for the [operational test] fleet to a full 3F production-representative configuration is going to take us longer than" anticipated, Bogdan said. "That is merely a function of trying to get those older airplanes fully mod-ed to a complete 3F hardware and software capability so they can do IOT&E with production-representative aircraft."

The delay has nothing to do with the ongoing software glitches that cause the jets' systems to shut down and need to be re-booted, a problem seen across the fleet, he said.

However, fixing these software issues did lead to a delay in wrapping up testing of the 3i software, which the Air Force needs to declare its F-35A jets operational this year. The work on 3i has eaten up "a majority" of the team's schedule margin for beginning IOT&E, officials at Edwards Air Force Base, California, told Defense News recently.

Bogdan has already acknowledged that delivery of the final Block 3F software slipped by four months to late fall 2017, a delay that was primarily due to the software issues seen in both 3i and 3F.

The joint program office is still negotiating with manufacturer Lockheed Martin on the long-delayed ninth and 10th batches of F-35s, valued at about $16 billion total, Kendall also said. Bogdan told reporters earlier this year that he expected to finalize the ninth low-rate initial production contract with Lockheed by the end of March, with the 10th following a few months later.

"We are in the final stages of that negotiation and hopefully it will be closed before too much time goes by," Kendall said.

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