What does Lockheed Martin have to do to mark the end, or close out, the System Development and Demonstration phase of the F-35?
The clearest explanation I have found, comes from the Congressional Research Service (www.crs.gov), from RL30563.pdf:
The F-35 is currently in low-rate initial production, with 280 aircraft delivered as of April 2018. At least 250 of those were in U.S. service. Four to five aircraft are currently delivered each month, with the production rate scheduled to increase to 120 per year by 2019. In keeping with the acquisition plan that overlapped development and production (known as “concurrency”), the F-35 was also in system development and demonstration (SDD), with testing and software development ongoing, from October 2001 until April 11, 2018. The SDD phase will formally continue until the end of Initial Operational Test and Evaluation, when a “Milestone C” full-rate production decision will be made.
A copy of the full PDF is available here:
We know from other sources that Initial Operational Test and Evaluation (IOT&E), will formally begin later this year, 2018.