Editor's note: This article, originally published Jan. 8, has been updated with an additional statement from the Air Force.

WASHINGTON — The US Air Force won’t lift weight restrictions on F-35 pilots until 2018 — at the earliest — as more testing needs to be done to address safety issues with the jet’s ejection seat, Defense News has learned.

"The [Joint Program Office] is working to accelerate the timeline for fixes and a lot of energy will be applied to ensuring this issue is resolved in 2017," Air Force spokesman Lt. Col. Christopher Karns wrote in a Jan. 9 email to Defense News. "However, getting this right is the top priority."

The news of the delay is another blow to the Pentagon's Joint Strike Fighter, which is fast approaching a critical deadline this year to declare the Air Force F-35A variant operational. The pressure is also on for the fighter jet to make its expected European debut at the Farnborough Air Show in the UK this summer. In an embarrassment for a program with years of cost overruns and schedule delays already under its belt, the plane was forced to skip Farnborough in 2014 after an engine fire grounded the fleet.

If 2014 was the year of the engine, 2015 was the year of the ejection seat. The issue has dogged the Pentagon since last summer, when Defense News revealed concern about increased risk of neck injury to pilots during low-speed ejections prompted the services to ground lightweight pilots. Testing of the seat, built by UK company Martin-Baker, last August showed an "elevated" risk of injury for F-35 pilots weighing under 165 pounds, and an "unacceptable" risk for those under 136 pounds, according to the Air Force.

The Pentagon is working with Martin Baker and aircraft maker Lockheed Martin on three fixes to the ejection seat problem: designing a lighter helmet to reduce pressure on the pilot's neck; installing a switch for lightweight pilots that will delay deployment of the main parachute; and mounting a "head support panel" between the parachute risers that will protect the pilot's head from moving backwards during parachute opening.

The JPO told Defense News in October that all three fixes would be fully implemented by summer 2017, allowing the services to look at lifting the weight restrictions. But in a Jan. 8 email, the Air Force acknowledged that the date had been pushed back, to early 2018 at the earliest.

"More tests have been conducted, and initial results look promising, but we still have a significant number of tests to conduct to validate and qualify the seat with the changes," wrote Air Force spokeswoman Maj. Kelley Jeter. "The three fixes: the head support panel, the weight selector switch and the lightweight Gen III helmet are scheduled to be ready for implementation by early-2018, and will allow Air Force leadership to lift the restriction that was put in place for lighter weight pilots."

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Although the Air Force did not give additional details about what specific tests have been done on the seat to date, JPO chief Lt. Gen. Chris Bogdan told Congress during an October hearing that the team had tested the seat at low speeds using lightweight mannequins (136 pounds and under) and with heavyweight dummies above 245 pounds. But at the time the program office had not tested the seat using a middleweight mannequin, representing most pilots, between 136 and 245 pounds. The JPO was planning tests in that weight envelope down the road, Bogdan said.