The lessons, however, are not considered major by Venlet, who describes the fixes as merely tweaks to various bolts and supports needed to ensure that maneuvers in the most stressing regimes can be executed. The first weapons test will include a bomb drop, followed later by the release of Raytheon's AIM-120C7, the medium-range air-to-air missile of choice for allied nations. Weapons testing was a major requirement for Lockheed Martin's portion of its fee for the F-35 development contract in 2012.

Though Venlet is satisfied with the progress of weapons testing on the aircraft, other work continues to lag. The Block 2A software—which will facilitate expanded weapons capability (such as the use of precision-guided munitions), improved sensor fusion in the cockpit and data-linking—was slated to be delivered late last year for testing. It will now be delivered to the fleet in low-rate-initial-production (LRIP) 4 aircraft at the end of this year, says Orlando Carvalho, F-35 vice president at Lockheed Martin. The 2A software is being tested by F-35As at Edwards AFB, Calif., and is slated to be used in training in July 2013, says Lorraine Martin, Lockheed Martin's F-35 deputy program manager.

This software is behind about three months, says Venlet. Though he characterizes the delay as small relative to the overall test program that continues through 2017, it is a “very serious three months for me,” he notes. When the program was rescheduled in 2010, some capabilities—including various radar modes, data-linking capabilities and messaging formats—were slipped to Block 2 from Block 1 in order to simplify the work into more achievable increments, he notes.

The 2A software, which has begun flying at Lockheed's facility in Fort Worth, was slated to be delivered for flight testing in midsummer, says Venlet. The lag is partly owing to a slip in developing the 1B software release last year. 1B will be delivered on the LRIP 2 and 3 aircraft, and includes basic navigation, communications, sensors and “limited simulated weapons,” according to government officials. This software package will be used for initial flight training at Eglin; currently aircraft there have the 1A software. The 1A package supports basic pilot training and qualification as well as maintenance training.

However, the 1B release to Eglin is near, according to government officials.

The U.S. Air Force needs the 1B software in order to begin its F-35A operational utility evaluation (OUE), a three-month phase of flying required to determine if the aircraft are ready to conduct routine training operations. Toth says his wing plans to use all six F-35As at Eglin for the OUE phase, and pilots will follow the 1A software syllabus, which will include only basic flying and navigation. The first six weeks of the plan will be restricted to academics for the trainees, and the final six will include flights.

Four pilots will participate in the OUE phase.

Data generated from the OUE, such as sortie turn rates and aborts, will be used by Air Education and Training Center Commander Gen. Edward Rice to assess readiness for formal training.

F-35A flights are ramping up from roughly eight per week in June to 14 in July and 16 in August, says Toth. The F-35B just began flying at Eglin and achieved 6.7 hr. in the air as of May, the latest available figure.

The Marine Corps plans an OUE process similar to the Air Force's prior to beginning formal pilot training for the F-35B, though the time required may be trimmed owing to lessons learned from the Air Force. The Marines, meanwhile, are required to conduct 120 hr. of local familiarization flights prior to beginning their own OUE.