First F-35 Test Aircraft Heading For Eglin Air Force Base

Software development involving the F-35 Lightning II sub systems is seeing multiple configurations being developed simultaneously as the new aircraft is progressing towards reaching initial operational capabilities later in the decade. Traditionally “evolutionary” approach would permit software-enabled capabilities to be incremented using the same code base while the aircraft program transitions from “training” to “war fighting” status. In the F-35 case, multiple teams are working on various software releases hoping to merge capabilities at a future stage of maturity. As a result various timetables describe the scope of remaining work done against the aircraft’s sub systems architecture. The road map we explore surveys the program’s development effort from the current Block 1 “Ready for Training” software configuration to the Block 4 “Enhanced War fighting” maturity target.

The F-35 presents major systems components whose  functionality does not fall within he realm of traditional software-enabled capabilities (flight sciences, training systems, etc). Rather the aircraft program is seeing a greater share of software development and integration bound to the innovative Prognosis Health Management System (PHM) and the powerful Autonomic Logistics Information Systems (ALIS) management and planning tool.

Autonomic Logistics Information Systems ALIS

ALIS is evolving as a major software development and integration undertaking whose complexity has been a source of schedule slips. The system is designed to improve the aircraft maintainability by providing direct visibility horizontally across maintenance, support, pilot, mission, logistics etc.. functions. In that realm, spare parts can be produced and inventoried in keeping with ALIS-generated components life cycle model. It forms a high value distributed information system implementing best practice Enterprise Supply Chain Management. In fact ALIS is at the heart of the F-35 JSF achieving major requirement of guaranteed “low cost” logistics throughout the targeted 30 years (or 8,000 flight hours) of service life. However, a Recent Quick Look Review document has stressed the multi-level risks associated with ALIS from a development standpoint:

the immaturity of ALIS development and the data integrity of aircraft configuration information are program-level sustainment risks which affect ALIS usability in test and operations. Concurrent development and production drives the need for multiple ALIS software releases in test and in the field which increases time and resources required to develop, correct and manage software.”

Structural Prognostic Health Management System (PHM)

With both on-board and off-board sub systems components, the F-35 Prognosis Health Management systems (PHM) plays the critical role of orchestrating the data flow between aircraft sensors linked to ALIS ground stations. This data flow can propagate relevant flight events correlated into valuable information for strategic fleet management insight; fleet sortie generation, customer support, suppliers and OEM as well as base management activities. With global logistics in mind F-35 operators derive tremendous benefits in support cost as well as optimal aircraft mission availability (an enterprise management approach with long range simulation and forecasting optimized towards the 8,000 flight hours/30 years service life target).

PHM Architecture: On-Board vs Off-Board systems

With its On-Board and Off-Board system architecture, PHM is tasked with fusing numerous sensors carried abroad the aircraft prior to offloading events information to off-board “health prognostics” processing.

The on-board air vehicle’s sensors monitor the health of flight critical, propulsion, airframe, mission and vehicle systems (over 100 parameters) recorded several events per second at frequency ranging from 20 events per second (Hz) to 80 Hz (320 Hz in aggregate). Some estimates credit the system for generating as much as 100-200 MB of data per flight hour which are recorded and preserved every 10 flight lifecycles in some cases.

The On-Board component of the PHM is interfaced to a vehicle support system interface with on-board diagnostics panel and to a portable memory device. The Off-Board Mission System (OMS) component which logs data recorded during flight provides maintenance debriefing insight and prognostics for intelligent logistics.

PHM Sensor Fusion

The sensor fusion paradigm promulgated by the PHM provides data as diverse as:

-Inertia and Strain sensor data (longitudinal, normal, lateral acceleration at the center of gravity) ,

-Engine Data (estimated total gross thrust feedback, estimated main nozzle thrust, main engine core speed, engine fan speed, ready to convert to jet, lift fan nozzle, pitch angle position,estimated lift fan thrust, estimated left and right roll nozzle thrust feedback, lift fan speed -physical/RPM, lift fan clutch status word),

-Control Surface (left & right flaperon angular position, left & right horizontal tail angular position, left & right vertical tail angular position),

-Air Data (angle of attack, static pressure measured, angle of sideslip, mach number, true airspeed, altitude rate) etc.

A prior GAO audit recognized this abundance of sensors as a factor in the growth of F-35 software code in comparison to previous aircraft programs: “The program’s software generation will integrate complex real-time interfacing of sensor “fusion”, weapons and fire control, maintenance and diagnostics, and propulsion and various actuated controls. The effort implements 8 times more software lines of code than found on the F/A18E/F and 4 times more than the F-22. Further growth of software code size soon became apparent “Software growth was 40% at preliminary design review, 13% after the critical design review. Recent programs saw 30 to 100% growth”.

F-35 Multiple Software Releases

A previous entry following the 2011 Selected Acquisition Report described the scope and pace of software development work for the program:

the initial limited release of Block 1 software was flown for the first time in November 2010 with Block I capability being implemented in software code at 81% (20M out of 24M software line of code). The road to Block 3.0 full warfighting capability scheduled for development in 2011-2014 has been charted through implementing the following blocks:

Block 0.1 (flight sciences 2006-2007),

Block 0.5 (initial mission systems architecture 2008-2010),

Block 1.0 (initial training capability 2008-2011),

Block 2.0 (initial warfighter capability 2010-2013) and

Block 3.0 (full warfighting capability 2011-2014).

The latest Quick Look Review has identified currently 8 flight releases versions being “manage(d) in System Design and Development; 4 for mission systems and 4 for Flight Sciences”. A Selected Acquisition Report also points to further complexity whenever functionality is added: “Additional mission systems capability is being added in each software block. The program has already encountered six weeks of down time on (test aircraft) AF-6 for software Block 1B, 2A, 2B which add weapons and more sensor fusion remains to be tested.”

F-35 software development phases:

Block 1

Block 1AReady For Training”

The first software release was incorporated into the first twelve F-35 delivered to Eglin Air Force base with basic “training capabilities” in the early phase of the program SDD (System Design and Development) testing phase in 2010 and 2011. These airframes covered the Low Rate Initial Production (LRIP) lot 1 and 2. The On Board software completed final flight testing with 44 sorties realizing 78.5 flight hours well on its way to receiving airworthiness clearance from the Air Force. Off board systems managed to reach government certification phase.

Block 1BInitial Training Capabilities”

This software implementation would bring timely Initial training capabilities to the System Design and Development phase. This software block permits simulating Air to Air and Air to Ground engagements and equips the 17 aircraft of the LRIP 3 lot with delivery schedule between late 2011 and late 2012. The12 aircraft using Block 1A configuration would be upgraded to Block 1B standard.

On Board systems have completed 25% of flight testing and are considered half way to production readiness. Mission systems appear poised with 99% of capabilities implementing new functionality for sensor fusion, electronic warfare and on board imagery as well as system security provisions. These systems have been partially tested (25% of flight test schedules undertaken) while production readiness testing has reached 50%.

Off board systems are still undergoing system integration and test rework for security certification and government acceptance while its mission systems components have incurred an additional 2.5 month schedule slip even though 99% test-verified.

The Off-Board Block 1B software validation regimen has completed 86% of the ALIS/HM test work and 82% of training system integration

Block 2

Block 2A “Advanced Capabilities”

Improving on the Block 1B, Block 2A systems include enhanced simulated air-to-air and air-to-ground training features incorporating weapons and electronic attack as well as tactical data sharing via the MADL (Multifunction Advanced Data Link) and Link 16 for interoperability. These features cover 32 aircraft of the LRIP lot number 4 scheduled for delivery from late 2012 to early 2013 and the 32 LRIP 5 aircraft due to arrive between early 2013 and early 2014. Following initial deployment on Cooperative Avionics Test Bed in October 2011, 70% of integration work had been completed as of November 2011.

For off-board systems, despite completion of requirement work, system integration and test rework marginally began. Code development code and unit tests have been completed though.

Block 2B “Initial warfighting Capabilities”

F-35 with the Block 2B configuration would in theory be Initial warfighting capable; capable of conducting actual tactical missions such as basic Combat Air Strike and interdiction, equipped with 2 GBU-12, 2 GBU-32 precision bombs, or 2 AMRAAM for air-to-air all internally carried.

Development phase for On-Board component was still limited to development code and unit tests.

Off-Board systems are also in code development and unit tests phase.

The Block 2B would also be available for retrofit on bpard the 64 Block 2A F-35 aircraft initially delivered as lot 4 and 5 and initially fitted with the Block 2A release.

Block 3

Block 3I (Initial) Tech Refresh 2

With only 30% into its development phase completed, the Block 3I (Initial) did no present a challenge other than being a Technical Refresh 2 version implementing the Block 2B variant on a hardware processor upgrade. The 38 aircraft of LRIP lot 6 due between early 2014 and early 2016, along with the 70 aircraft of LRIP lot 7 due from early 2015to early 2016, will share similar operational capabilities with the 64 Block 2B aircraft. Development work onto the off-boards air craft have been lagging that of the Block 2B ones.

Block 3F (Final) Full War Fighting

This software release would pave the way for the F-35 to conform in full to “war fighting” status as defined in the project Operational Requirements Documents. The 110 aircraft scheduled for delivery as LRIP lot 8 between early 2016 to early 2017 will display the Block 3F build. The LRIP lot 9 aircraft due probably beyond 2017 have not yet been accounted into a order schedule. When retrofitted onto LRIP 6 and 7 aircraft, the Block 3F (“Final”) software release will be the definitive F-35 war-ready configuration. It is estimated that on-board systems definition requirements are still being finalized.

The 2012 selected acquisition report relates the note of caution emitted by legislators regarding progress on the Block 3 configuration: “Under the recently revised F-35 schedule the committee notes that development of block three hardware and software components will not be complete before 2015 and believes that the request to procure kits to retrofit 25 LRIP F-35A aircraft to the block three configuration is premature. Accordingly the committee recommends $7.6 million, a decrease of $86.6 million for F-35A modifications.”

Block 4

In a similar fashion, SAR 2012 reports the deferment of Fiscal Year 2014 $115.7 million funding for the development of Block 4 “Enhanced war fighting mode” that would improve on the Block 3F build on account of additional program risks.


The F-35 software development program represents concurrency development with all its main attributes of risks, delays and inefficiencies applied to an already complex, delay-prone undertaking. The concurrency quick look review of November 29th 2011 considers the F-35 design as still not mature on account of the basic design awaiting the incorporation of numerous changes and modifications. Given the 18 to 24 months median time span required for design modifications to be incorporated,the 725 currently identified Change Requests carry the potential to push the program to the brink.

The discovery of newer software defects, bugs or shortcomings on the aircraft’s multiple software Block releases is likely to further stretch the program current SDD testing phase.



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