The number of remaining design flaws is one thing, but the 2019 annual operational test report also highlights their persistent nature. The F-35 entered operational testing in December 2018 with a large “technical debt” of problems that had been identified but not corrected during developmental testing, as the Pentagon’s testing office reported earlier this year. Of the 873 deficiencies identified by the testing office as of November 2019, approximately 576, or 66%, were carried over from the development phase. The program’s technical debt has only grown during operational testing as evaluators keep discovering new flaws, and the testing office’s report cautioned that the unresolved flaws “should be addressed by the program to ensure the SDD [System Development and Demonstration] baseline configuration of software and hardware is stable, prior to introducing a large number of new capabilities to the software in the new hardware configuration associated with Block 4 [future development].”

What the testing office is saying in engineering parlance is that the endlessly patched software controlling all the F-35’s components and mission systems is unstable. The “computer that happens to fly” is a densely integrated network of hardware, software, weapons, and mission data. Making a software change to any one component can, and often does, have unintended negative effects on a seemingly unrelated component. The testing office wants to see the program correct all the existing flaws so the F-35 has a stable base on which to build as designers and engineers add new capabilities in the coming years. Unless this occurs, every time a new function is added, they will likely end up piling new flaws on top of old flaws, which will end up endangering schedules and increase costs.

Despite the triumphant 2018 proclamations that the program had completed its troubled development process, the testing office has reported that development “may take years to complete.” Meanwhile, F-35 pilots today are dealing with the effects that “may be observed from both operational testing and fielded operations.”

