The F-35 program has fixed one of the Lockheed Martin [LMT] fighter’s Category 1B deficiencies and looks to resolve another two by the end of the year, while the remaining fourth Category 1B Deficiency Report (DR) will require development, the F-35 Joint Program Office (JPO) said.

“One DR requires technology development to resolve,” the JPO wrote in an emailed response to questions this week.  “An assessment was recently completed, and a multipart solution has been selected.  Funding and closure timeline are currently being determined.”

F-35 testers and operators log such DRs, which normally represent specific, and sometimes rarely undertaken points in the flight envelope, rather than systemic deficiencies in the entire flight envelope. Logging such DRs and retaining them allows testers to evaluate system flaws and determine how often they occur in flight.

The F-35 JPO said that the four Category 1B deficiencies qualify as Controlled Unclassified Information (CUI) and thus the program declined to identify them or elaborate on planned fixes. Category 1B deficiencies are those that represent a critical impact to mission readiness, while more serious Category 1A deficiencies are those that entail a risk to life or the loss of the aircraft.

Three of the four F-35 Category 1B deficiencies, partially discussed in Government Accountability Office (GAO) reports in April and last month, appear to be related to some inaccuracy of the U.S. Air Force F-35A’s 25mm gun and increased vibration stress on the airframe; cockpit overpressurization at one point of the flight test envelope; and unreliable horizon imaging on dark nights from the night vision camera of the Helmet Mounted Display System (HMDS) that can reveal a “green sparkle” to pilots.

Collins Elbit Vision Systems, LLC–a joint venture between Collins Aerospace [RTX] and Israel’s Elbit Systems Ltd. [ESLT] through its Fort Worth-based subsidiary, Elbit Systems of America—builds the HMDS.

A source said that the DR requiring further technology development is likely the “green sparkle” and that the F-35’s Technology Refresh 3–the enabler of the aircraft’s future Block 4 weapons and other improvements–may involve a hardware and firmware fix to reduce latency so that the HMDS’ optics can accept a higher data rate and so that messages will feed the optics more quickly in order that the optics not interpret an information gap and generate the “green sparkle.”

The source said that the cabin overpressurization DR stemmed from one, anomalous data point in the flight test envelope and that the program determined that the DR was not a risk to pilots in the field.

The Category 1B gun deficiency was confined to the F-35A, as gun lugs were backing out during firing, but the program will likely address that with more frequent inspections, per the source.

The F-35 JPO said that, of the four Category 1B deficiencies in this year’s GAO reports, one “has been closed as verified/corrected,” and the other three, including the one that requires further development, are open.

“Two DRs are awaiting verification of fixes,” per the F-35 JPO email this week. “One started verification flight tests in late Q1 [quarter one of] CY [calendar year] 2022 that will continue through a portion of CY 2022. Tests so far indicate the fix is working. Closure verifying correction is expected before the end of the year.”

“The other DR fix implementation recently completed verification testing in May 2022,” per the F-35 JPO. “Data analysis from testing is underway and closure will occur once analysis confirms correction, expected before the end of the year.”

Last month, GAO’s annual weapon systems assessment said that “while the [F-35] program found new performance deficiencies in the past year during operational testing, the total number of performance deficiencies the program is tracking decreased slightly as more were resolved.”

The GAO assessment said that 822 F-35 Category 2 deficiencies remain. Ranking below a Category 1 DR in seriousness, Category 2 DRs are those that may impede or constrain mission accomplishment.