Joint testing clears F-35B/C for night refueling

A Marine Corps F-35B Lightning II from Air Test and Evaluation Squadron (VX) 23, Naval Air Station Patuxent River, undergoes ground testing of an improved probe light assembly in a hangar at Edwards Air Force Base, Calif.

The F-35 Lightning II program recently completed testing on an improved lighting assembly with the KC-135 that will enable the Navy and Marine Corps F-35 variants to refuel behind the tanker at night. Flight testing of the redesigned light, which attaches to a refueling probe, was led by the Patuxent River Naval Air Station test team and supported by the team at Edwards Air Force Base.

The test evolution demonstrated teamwork across three services and two test units located on opposite coasts, all focused on quickly evaluating this lighting fix under specific nighttime conditions to ensure that F-35 operators can expand their night refueling operations to include all configurations of the KC-135.

The purpose of the probe light on Navy and Marine aircraft is to illuminate the refueling receptacle, or “basket,” to ensure that the F-35 pilot can see adequately and make contact to begin refueling. However, the existing lighting design made it difficult for the KC-135 boom operator to see the silhouette of the F-35. Under the Air Force requirement, the boom operator monitors refueling operations and helps the F-35 pilot maintain safe separation from the refueling boom. One of the redesign’s objectives is to ensure better visibility for the KC-135 boom operator.

“The current probe light was too bright, blinding the KC-135 aerial refueling boom operators,” said Michael McGee, 418th Flight Test Squadron (FLTS), aerial refueling project manager at Edwards AFB. “The new light was designed to be less bright, but still bright enough for the F-35 pilot to see clearly.”

For this test, an F-35B from Air Test and Evaluation Squadron (VX) 23 at Patuxent River deployed to Edwards AFB and paired up with a KC-135 and test aircrew from the 418th FLTS. Both ground and flight tests posed interesting challenges for the teams.

“For the ground test we used a hangar,” McGee said. “The environment needed to be completely dark. We had to remove emergency lighting from the facility and place mats on the floor to reduce light glare. The boom operators were on a scissor lift to simulate the KC-135 tanker. The team had to simulate the drogue basket approaching the F-35B so the 461st FLTS maintainers mounted the basket onto a B-4 stand. Since the stand is on wheels, we could simulate the basket approaching the probe while the F-35 pilot assessed the brightness of the light.”

The ground test evaluated two types of lights with different color tones—a warm white light and an amber light—across various brightness levels. The warm white light was determined to be the best choice for both boom operators and pilots, McGee said.

The first flight test lasted four hours and accomplished all of the required test points.

“Our biggest concern was completing the test during the lowest moon illumination; worst-case lighting scenario timeframe, which was March 1-11,” McGee said. “For the flight test, we planned a minimum of two flights, but captured all test points on our first flight.”

Based on favorable results, the design is being evaluated by the Air Refueling Certification Agency this summer and, once approved, will be incorporated into a revised flight clearance for the Navy and Marine Corps.

The F-35A—the Air Force variant—does not have a probe so no light change is required for that model.