Aerial refueling probe light evaluations flown with KC-135: Effort to clear Navy, USMC F-35 night refueling envelope
By Kenji Thuloweit, 412th Test Wing Public Affairs
/ Published March 29, 2019
EDWARDS AIR FORCE BASE, Calif. (AFNS) -- The F-35 Lightning II program recently completed testing on an improved lighting assembly with the KC-135 Stratotanker 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 Patuxent River Naval Air Station, Maryland, and supported by Edwards Air Force Base, California.
The test demonstrated teamwork across three services and between 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, which is an Air Force requirement in order for the boom operator to monitor refueling operations and help the F-35 pilot maintain safe separation from the refueling boom. One main objective of this redesign is to ensure better visibility for the KC-135 boom operator.
“An issue with the current probe light was that it was too bright, blinding the KC-135 aerial refueling boom operators,” said Michael McGee, 418th Flight Test Squadron 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 deployed to Edwards AFB from Air Test and Evaluation Squadron 23, or VX-23, Naval Air Station Patuxent River, and was paired up with a KC-135 and test aircrew from the 418th FLTS. Both ground and flight tests posed interesting challenges for the team consisting of 418th FLTS and 461st Flight Test Squadron personnel.
“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 raised 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 aircraft maintenance 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 assessed as the best choice for both of the 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.”
The evaluation had favorable results and the design will now be considered by the Air Refueling Certification Agency to be incorporated into a revised flight clearance for the Navy and Marine Corps, anticipated by early this summer.
The F-35A — the U.S. Air Force variant — does not have a probe so no light change is required for that model.