WASHINGTON — In response to reports of hypoxia-like symptoms experienced by F-35A pilots at Luke Air Force Base, Arizona, the program office intends to make changes to the onboard oxygen generation system to optimize the flow of oxygen to those flying the jet.

The modification to the onboard oxygen generation system, or OBOGS, involves refining the algorithm associated with oxygen concentration, an F-35 joint program office spokesperson explained in a statement to Defense News.

"There is no indication the delivered oxygen concentration was a contributor to any of the recent events," said Brandi Schiff. However, by tweaking the levels of oxygen associated with varying altitudes, the office may be able to help prevent further physiological incidents from happening.

Honeywell, the manufacturer of the F-35's OBOGS system, will be responsible for designing upgraded firmware as well as a path to retrofit all variants of the joint strike fighter with the new capability, she said.

"Cost estimates are still being developed," Schiff said. "The current time estimate is 24 months, but the F-35 joint program office, or JPO, is pushing [F-35 prime contractor] Lockheed Martin to accelerate the fielding of this new firmware."

On June 9, officials at Luke AFB announced that it would pause F-35 flight operations at the base because of five incidents when pilots experienced symptoms similar to hypoxia, or oxygen deprivation. Experts from the program office were dispatched to the base, where they conducted testing and analysis for a week without reaching a solid conclusion on what had caused the episodes.

Brook Leonard, commander of the 56th Fighter Wing at Luke AFB, ultimately made the decision to restart F-35 flight operations on June 21 after implementing several protective measures such as flying the aircraft at lower altitudes and increasing the minimum levels for backup oxygen systems.

Although the issues with the F-35 have been limited to the A models at Luke AFB, finding the root cause of physiological incidents like hypoxia has proved to be a difficult problem for all of the military services across a wide array of aircraft. The U.S. Navy has had little luck discerning the cause of similar symptoms exhibited by T-45 trainers and F/A-18 Hornets. Further complicating the issue is that the symptoms of oxygen deprivation are very similar to other conditions, like having too much oxygen in the blood or oxygen contamination, making it hard to parse whether the blame can be attributed to just one problem.

There has been only one physiological incident at Luke AFB since flights resumed, said Maj. Rebecca Heyse, a spokeswoman for the base. On July 10, a pilot experienced "hypoxia-like" symptoms during a flight, but inspectors were quickly able to find the culprit: an irregular oxygen valve that has since been replaced. The U.S. Air Force views this as an isolated event that is unconnected to the still-unexplained earlier episodes.

Investigation into the physiological events is ongoing, with the JPO, F-35 physiological event team, the U.S. Air Force’s 711 Human Performance Wing and the Navy Medical Research Unit Dayton all engaged in analysis, Schiff said.

The U.S. Air Force and JPO couldn’t rule out a larger, systemic problem with OBOGS in their initial investigations and plan to do further evaluation. For instance, they will take the F-35s involved in the physiological incidents and conduct "extensive testing" to ensure that all OBOGS components were working properly. They also plan to assess whether life support systems like OBOGS are meeting reliability requirements and conduct air quality tests on Luke AFB jets to ensure oxygen is not being contaminated.

Additionally, Schiff noted that the JPO is evaluating "potential improvements and opportunities for implementing additional sensing capability, including redundant oxygen sensors and a suite of air quality sensors."

A team of officials from the JPO, U.S. Air Force F-35 integration office and 711 Human Performance Wing is set to arrive at Luke AFB on Wednesday to begin an eight-week "heat exhaust study," Heyse said.

The team will study how the aircraft ramp is set up and assess temperature and air quality data to ensure pilots are not suffering negative effects on the ground before takeoff that could be exacerbated during flight, she said.