F-35 test pilots will begin flying this year with a third-generation helmet mounted display system (HMDS) that incorporates modifications to the earlier-generation display system, which the Pentagon has identified as an F-35 program risk. The fixes the fighter program developed for the “Gen 3” helmet system persuaded the Pentagon’s F-35 Joint Program Office (JPO) to stop funding an alternate helmet-mounted display.

“I definitely have confidence that we are on the right track; we have the right plan for these fixes in place,” said Marine Lt. Col. Matthew Kelly, government flight test director at the F-35 integrated training center at the Naval Air Station Patuxent River, Md.

In 2011, the Department of Defense identified the HMDS as one of several F-35 program risks. It found that the Gen 2 system being developed by the joint venture between Rockwell Collins and Elbit Systems of America—then called Vision Systems International (VSI)—was deficient in the areas of night-vision acuity, display jitter during aircraft buffeting and image latency from the fighter’s electro-optical distributed aperture system (DAS). In September 2011, F-35 prime contractor Lockheed Martin awarded BAE Systems a contract to develop an alternate HMDS with detachable night-vision goggles (NVGs) in the event VSI failed to resolve issues with the incumbent helmet-mounted display.

Last October, after testing display-system fixes over the course of two years, the JPO gained enough confidence in the new Gen 3 HMDS to stop BAE’s parallel display effort. In an interview with AIN, Kelly, an F-35 test pilot, described some of the testing that took place during the intervening period between the start and termination of the alternate HMDS development.

The night-vision acuity of the Gen 2 HMDS, which contains an ISIE (Intevac silicon imaging engine) 10 sensor for low-light-level detection, was the helmet system’s major deficiency, according to Kelly. An ISIE 11 sensor based on Intevac Photonics’ patented electron bombarded activated pixel sensor (EBAPS) technology brings the system’s night-vision acuity closer to the 20/20 vision NVGs can provide.

Last summer, the F-35 program tested a production-representative night-vision camera with ISIE 11 sensor in a modified Gen 2 helmet, using a twin-engine King Air surrogate aircraft. Flying from St. Mary’s County Regional Airport in Maryland, close to NAS Patuxent River, pilots tested the system in high- and low-light conditions and compared it to using ANVIS 9 NVGs. Testers also used a ground-based laser designator to determine how far away pilots could spot a laser pointer. “There were some limitations to the test,” Kelly acknowledged. “It wasn’t in an F-35, but it was close enough that we could make a confident decision about the usability and the effectiveness of the new ISIE 11 night-vision camera in the Gen 3 helmet.”

In a separate interview with AIN, Drew Brugal, Intevac Photonics general manager, said “the plan had always been” to eventually deliver the ISIE 11 sensor, which was not mature when the company was contracted to provide integrated night imaging for the F-35 HMDS. Last fall, Intevac started delivering ISIE 11 sensors to the Merrimack, N.H. operations of Elbit Systems of America, which builds the sensor into the night-vision camera.

Brugal formerly headed VSI, which the partner companies dissolved in 2012 after his departure and replaced with a new organization, Rockwell Collins ESA Vision Systems. The joint venture with Elbit “was restructured to provide a more efficient and agile operating structure for the business,” according to Rockwell Collins. The companies “continue to be equal partners in the joint venture with similar product and technology responsibilities as before; however, program offices of the company’s product line management were transitioned from VSI to the parent companies.”

The Gen 2 helmet system’s latency, or response time at importing DAS imagery—measured in milliseconds—was not the problem testers thought it would be, Kelly said. Pilots just hadn’t had the opportunity to use the DAS sensor array during flight testing. Test pilots experienced display jitter in areas of the F-35 flight envelope that hadn’t been approved for training, he said. The program addressed the problem by integrating micro inertial measurement units and filtering algorithms in the HMDS to cancel out jitter effects. Pilots flew the fixes using a modified Gen 2 helmet.

“It’s still not perfect, but it’s the 95-percent solution and the major issue there is resolved,” Kelly said.