A lingering problem with the F-35’s high-tech helmet obscuring the pilot’s vision has prompted U.S. Air Force investigators to call for adjustments to the system, while the service is not following the U.S. Navy and Marine Corps’ effort to retrofit a fix for the “green glow” issue.
The problem forced an F-35A pilot to rapidly pull away from a wingman and refueling tanker during a night operation earlier this year because the green glow caused him to become disoriented and unable to see the nearby aircraft, according to a safety investigation report.
The Air Force incident is similar to situations that Navy and Marine Corps pilots found themselves in during dark night carrier landings, with the glow obscuring the ship and its flight deck. In response, the Navy initiated a capability requirement to address the problem, and the F-35 Joint Program Office (JPO) began a phased Organic Light Emitting Diode (OLED) capability development to replace the projection technology in the helmet, the JPO said in a statement.
The retrofit replaces the helmet’s liquid crystal display (LCD) with the OLED technology, which can provide a clearer image in low light. While these upgrades are underway, the Air Force and international F-35 operators have not determined a requirement for the new capability.
The January incident in Alaska detailed the possible threat of the green glow during night operations. At about 6:10 p.m. on Jan. 6, 2021, an F-35A pilot with the 356th Fighter Squadron at Eielson AFB, Alaska, was on an initial night checkout flight led by an instructor pilot in another F-35A. The task for the night was basic surface attack with an introduction to night air-to-air refueling in the nearby Paxon military operating area.
The night was dark, with the Moon below the horizon, when the two-ship formation joined up with a KC-135R for the refueling training. The instructor pilot moved to take on fuel first, but he could only see the tanker’s beacon intermittently, and briefly stopped the rejoin because the tanker’s lights were too low. Once the KC-135 boom operator turned up the tanker’s light, the instructor pilot then moved to rejoin and took on 3,000 lb. of fuel.
Once disconnected, the instructor moved to observe his wingman from under the KC-135R’s right wing. The tanker started a 10-20 deg. left bank turn, and the second pilot struggled to maintain contact for about 5 min. The aircraft flew through light clouds, and the instructor pilot began to struggle to see his wingman.
Green glow from the helmet, combined with low tanker lighting and hazy clouds, obscured the view of the other F-35 attempting to refuel and the tanker itself. The illumination from the helmet display was so bright that the pilot needed to tilt his head and look below the display to try to see his environment.
After about 2-3 min., the pilot felt the “leans” of disorientation and more frequently checked the F-35’s Electronic Flight Instrument to try to gain situational awareness, according to the investigation. As the tanker rolled, the instructor pilot realized he was “Type-1 Spatially Disoriented,” meaning he was totally blind to what was going on around him. The pilot went to max afterburner, checked away to the right and climbed 10 deg. nose high, calling on the radio “Number 1 is Spatial D’d, climbing in max afterburner.”
The upgrade pilot then radioed “Knock it Off” to halt all training. The instructor climbed away, setting autopilot for flight level 300 and 300 knots indicated air speed. The pilot stayed on autopilot for several minutes, though he felt normal after about 30 sec. The night refueling was terminated and the F-35s safely returned to Eielson.
A brief Air Force safety investigation into the incident, released to Aerospace DAILY as part of a Freedom of Information Act request, said the incident was the result of Personal Equipment Interference and the use of “Poorly Designed or Unsuitable Equipment.”
“The [instructor pilot] repositioned his head to avoid the F-35 helmet green glow, when combined with a lack of natural lighting and the tanker lighting, the [instructor pilot] experienced Spatial Disorientation,” the Air Force Safety Center report said.
The F-35 pilot’s Helmet Mounted Display has three brightness settings—for night, day and auto. The day mode’s setting default is 500 foot-lamberts and the night’s default is 25 foot-lamberts. The report says the brightness in the lowest setting was a “causal factor” for the incident.
The report included a recommendation that the helmet’s brightness at its lowest level is too bright for night air-to-air refueling, and the helmet’s green lighting power output needs to be adjusted to make the lighting more dim.
“This would help pilots avoid having to reposition their heads to avoid the glow,” the report says.
The Eielson incident is at least the second in about eight months involving an Air Force F-35A. On May 19, 2020, an F-35A crashed as it was landing during a night flight at Eglin AFB, Florida, with the pilot able to eject. An Air Force Accident Investigation Board report found the pilot was increasingly distracted throughout the descent by the “green glow,” which affected his visibility, especially just before touching down. A misalignment of the Helmet-Mounted Display also caused him to misunderstand his altitude during landing.
The problem of the “green glow” has been reported since 2012, with the biggest concern being its impact on night carrier landings. The Defense Department’s Director of Operational Test and Evaluation in 2016 said the issue was a “Category 1” deficiency, affecting the safety of flight.
The JPO in a statement said its development effort prioritized an immediate engineering solution for Navy and Marine Corps F-35Cs, with 62 OLED helmets already delivered. Another 62 are expected in May 2022. In September 2021, the JPO contracted with Lockheed Martin to mature the current design for a long-term fix. Once this is tested, the JPO plans to buy production and retrofit helmets for Navy and Marine Corps F-35C pilots and, if required, the rest of the F-35 community.
“The other F-35 member services of the F-35 Partnership did not prioritize the OLED capability requirement, and hence were not part of the original OLED procurement for USN and USMC,” the JPO said.
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