Deliveries of new F-35 Lightning II engines, as well as the modern stealth aircraft itself, have been paused as the military investigates what led a variant of the aircraft to crash on a runway in Texas last month.
The F-35 Lightning II Joint Program Office told Military.com in an email Thursday that, with some models of the aircraft being grounded following the Dec. 15 incident, it has paused delivery of the fighter jets from production facilities. Additionally, defense contractor Pratt & Whitney -- which makes the F135 engines for the jet -- and the military services have agreed to stop engine deliveries during the maintenance inspections.
"Flight operations restrictions have been imposed at all F-35 Production facilities, which has had the effect of halting aircraft deliveries," the F-35 Joint Program Office said, adding it has also delayed delivery of F135 engines "until further information from the investigation is known and safety of flight can be ensured."
Read Next: Air Force Will Now Consider Advanced Academic Degrees in Some Promotions
Having deliveries of new engines halted could be a sign of progress toward getting some models of the F-35 back in the air, according to Jeremiah Gertler, a senior associate with the Center for Strategic and International Studies think tank in Washington, D.C., who specializes in aviation.
"Engine deliveries being stopped implies they are checking to see if it is an engine issue, or have identified an issue and are working on a fix," Gertler told Military.com on Thursday.
The halt in deliveries comes three weeks after an F-35B Lightning II crashed during a vertical landing at a Naval Air Station Joint Reserve Base Fort Worth runway on Dec. 15.
Video footage posted online by CBS News' Dallas-Fort Worth station showed the F-35B attempting a vertical landing when, shortly after touching down, the aircraft's nose cone smashed into the ground and the jet began to rapidly spin.
The pilot ejected from the jet, according to the footage, and his parachute opened just before hitting the ground.
The pilot, an Air Force major who had been doing performance quality checks on behalf of the Defense Contract Management Agency, was released from the hospital shortly after the crash and suffered only minor injuries.
On Dec. 28, the F-35 Joint Program Office told Military.com that some models of the F-35 had been grounded "while the investigation into the mishap on December 15 continues" but did not disclose numbers or any other specifics.
Ann Stefanek, a Department of the Air Force spokesperson, told Military.com on Dec. 30 that the service "currently has a small number of F-35As that will not fly" as a result of directed grounding but did not provide any other specifics.
The Department of the Navy did not return a Dec. 30 request for comment asking how many F-35s had been grounded by the Navy and Marine Corps following the Dec.15 crash.
Lockheed Martin, the contractor for the F-35 Lightning II, delivered 141 of the aircraft in 2022, according to a Dec. 30 press release, which was just shy of the 148 that the company was scheduled to deliver. The groundings caused by the Dec. 15 incident led to the shortfall.
"The F-35 team was on track to meet the commitment of 148 aircraft as planned; however, due to a temporary pause in flight operations, which is still in effect, necessary acceptance flight tests could not be performed," Lockheed Martin said in its statement.
-- Thomas Novelly can be reached at email@example.com. Follow him on Twitter @TomNovelly.
Related: Military Grounds Some F-35s Following Crash in Texas