F-35 Modifications

F-35 Modifications is the U.S. Air Force procurement line for retrofitting F-35A Conventional Take Off and Landing (CTOL) aircraft and their integrated air systems. It sits within Aircraft Procurement, Air Force, Budget Activity 05, Modification of Inservice Aircraft, and the Tactical Aircraft budget subactivity. The work corrects documented safety, maintainability, structural-life, and system deficiencies while bringing earlier aircraft closer to evolving fleet configurations. Field teams and depots install changes to navigation, weapons, avionics, survivability, mission deployment, and other capabilities.

The FY2027 request is based on an F-35A total active inventory of 541 aircraft. It combines discretionary funding for deficiency correction, Block 4, APG-85 radar, propulsion, and reliability and maintainability products with mandatory reconciliation funding for Block 4 retrofit products. The request rises because more modification kits are being procured; installation of engineering change proposal (ECP) kits bought with mandatory funding remains a baseline requirement from FY2028 onward. Air Force initial operational capability occurred in August 2016, and full-rate production was approved in March 2024.

Block 3i LRIP 2 5 Upgrade was an earlier step toward a common Block 3F fleet. It upgraded Block 1B, 2A, and 2B aircraft from low-rate initial production (LRIP) lots 2 5 with radar modules, Integrated Core Processor (ICP) modules and rack, electronic warfare (EW) modules, and the Gen III Helmet. The effort also provided depot tooling and test equipment. Its purpose was to prepare early aircraft for later capability upgrades and avoid maintaining numerous configurations at operating locations; no FY2027 funding is requested.

Block 3F LRIP 2 5 Upgrade supplied software and installation work for 46 aircraft and integrated systems that had received Block 3i hardware. Block 3F LRIP 6 8 Upgrade performed the corresponding baseline upgrade for 56 aircraft from later LRIP lots. Both efforts aimed to provide full Block 3F warfighting capability and reduce configuration differences across the fleet. Neither requests FY2027 funding.

Concurrency addressed deficiencies discovered after formal acceptance of aircraft built while development continued. Changes were approved by the Joint Configuration Control Board and prioritized in a requirements document reviewed by the services and partners every six months. Its remaining Digital Tuner Insertion Program (DTIP) converts Lots 5 10 toward a Lot 11 configuration: their digital radio-frequency-memory equipment is incompatible with Technical Refresh 3 (TR-3). DTIP installation alongside TR-3 upgrades in FY2026 supports standardization of training and combat-coded aircraft; this line has no FY2027 request.

Correction of Deficiencies funds FY2027 ECP material, engineering, installation labor, and depot support. Its principal effort, Structural Life Limited Parts 2 (SLLP2), comprises 24 ECPs intended to remove structural life limits below 4,000 flight hours. Follow-on SLLP3 addresses limits between 4,000 and the aircraft's intended 8,000 hours; FY2027 work continues nonrecurring engineering on priority ECPs and kit procurement. Ogden Air Logistics Complex support includes modification management and supplementary work needed to return inducted aircraft safely to flight status.

Block 4 Modifications delivers advanced capabilities through recurring hardware and software updates rather than a single block conversion. FY2027 procurement includes TR-3-related work and Pre-42Px kits, while the program also prepares 42Px Kit A and Kit B retrofits. TR-3 adds a new ICP, Panoramic Cockpit Display, and Aircraft Memory System; Pre-42Px adds communications processing, EW antenna modules, and cooling. Kit A modernizes EW processing, while Kit B enables capabilities including full-motion video, enhanced radar-warning coverage, navigation and communications improvements. Simulator software and logistics systems must change alongside aircraft hardware.

APG-85 Retrofits are identified as a distinct FY2027 funding purpose within the Block 4 request, with retrofit procurement and depot installation planned in later years. The Block 4 schedule generally places retrofits one year behind production to account for manufacturing ramp-up and hardware technical risk. Delays to TR-3 shifted some equipment into the separately identified Pre-42Px kit; other production timing changes reshaped Kit B. Tooling investment supports the manufacturing rates needed to deliver these capabilities to fielded aircraft.

Propulsion supports FY2027 material for F135 engine changes intended to improve readiness, reliability, maintainability, and availability while addressing production deficiencies and obsolescence. Pratt & Whitney modifications include fan-power lockwireless fittings, a multi-attitude deaerator gearbox redesign, fuel-pump gearing, nozzle-linkage durability, fuel-throttle-valve bellows, the main oil pump, and a high-pressure-turbine honeycomb change. Installation occurs at depot or unit level as aircraft and resources become available.

Reliability and Maintainability separately targets F-35A readiness degraders, cost per flight hour, obsolescence, and life-cycle costs. FY2027 funding purchases modification kits and covers support and field-team installation as critical issues are identified and ECPs prepared. This effort transitioned from the correction-of-deficiencies category in FY2022. Together, these distinct lines sustain fielded aircraft while structural repairs and successive capability retrofits proceed.