The Lockheed Martin F-35 Joint Strike Fighter has completed the nearly 12-year System Development and Demonstration (SDD) phase of the program.

The final SDD test flight was conducted on April 11 at Naval Air Station Patuxent (PAX) River by F-35C development jet CF-2 which completed a loads data mission while carrying external 2,000-pound GBU-31 Joint Direct Attack Munitions (JDAM) and AIM-9X air-to-air missiles.

“Completing F-35 SDD flight test is the culmination of years of hard work and dedication from the joint government and industry team,” F-35 Program Executive Officer Vice Admiral Mat Winter said in a statement.

Since the first production representative F-35 AA-1 flew in 2006,the program has conducted 9,200 flights over more than 17,000 flight hours, and has completed more than 65,000 test points. The test fleet comprised all three variants from the US, UK and The Netherlands, and these were based at Edwards AFB in California, and at Pax River  near Washington DC.

The completion of SDD sees the Block 3F operational flight program software load released for operational test and evaluation (OT&E), and should clear the way for the approval of full rate production.

“The F-35 flight test program represents the most comprehensive, rigorous and the safest developmental flight test program in aviation history,” said Greg Ulmer, Lockheed Martin’s vice president and general manager of the F-35 program. “The joint government and industry team demonstrated exceptional collaboration and expertise, and the results have given the men and women who fly the F-35 great confidence in its transformational capability.”

The JSF program has suffered from its share of development issues throughout the SDD process which has seen service entry for US and partner nations delayed by up to five years, but to-date no aircraft has been lost during development.

Program critics have often pointed to the concurrent process of SDD being ongoing while low-rate production was underway as contributing to the delays. This concurrency has also resulted in more than a hundred early production aircraft requiring structural fixes and other upgrades, including Australia’s first two F-35As which were produced in low rate initial production (LRIP) lot 6 and recently completed their rework at Hill AFB in Utah.

Flight testing of the F-35 will continue throughout the type’s expected 40+ year service life as new software loads, hardware refreshes, weapons and other enhancements and capabilities are added to the aircraft.