The US Navy and industry will pursue a next-generation on board oxygen generator system (OBOGS) while the service implements fixes to mitigate persistent oxygen and pressurization issues on its Boeing/BAE Systems T-45 trainers and Boeing F/A-18E/F Super Hornets.

Following a comprehensive review of physiological events on the T-45 Goshawks and F/A-18E/F fighters, the navy concluded the OBOGS on both aircraft are not able to provide clean, dry air to pilots and can even allow contaminants to escape into their breathing air that can cause hypoxia. The navy found pressurization issues caused most of the oxygen problems for F/A-18E/F pilots, while the OBOGS emerged as the culprit on T-45s,

In a 15 June call with reporters, vice chief of naval operations Adm Bill Moran admitted that while the report found issues with the OBOGS and the F/A-18E/F’s environmental control system, which provide air for pressurization, heating and cooling, the root cause of hypoxia remains elusive.

“Root cause to me is if you identify a specific system or event or environmental condition that causes a hypoxic event or a pressurization malfunction,” Moran says. “When I say we haven’t found the cause, it may be more than one component or condition that clearly leads to a physiological event. So what we’re doing is systematically going after anything that contributes to the cleanliness, the dryness and pressure of air at any stage of ground or flight operations.”

However, the navy’s review team discovered T-45's OBOGS does not have a water separator mechanism, even though the service fields a similar mechanism on OBOGS in high performance jets, Moran says. When water interacts with contaminants in the OBOGS, it can release the contaminants into the aircrew breathing air. The navy will install water separators on T-45s by this fall, Moran says.

In parallel with ongoing mitigation efforts, industry will install breathing air pressure warning for aircraft fitted with the solid state oxygen monitor (CRU-123) this month and develop a next-generation OBOGS known as GGU-25.

T-45’s current OBOGS is made up of Cobham’s oxygen concentrator (GGU-7), an oxygen monitor (CRU-99) and an aircrew-worn breathing air regulator (CRU- 103).

The CRU-123 is a digital upgrade to the current CRU-99 and will be able to deliver information on both temperature and oxygen pressure to pilots, Moran says. Cobham is looking at the redesigned OBOGS as a potential replacement for the legacy system if the navy’s mitigation efforts do not work, he adds. The effort also includes adding a larger capacity emergency oxygen system on the T-45 to eliminate the current way the navy uses on board oxygen today.

“So we’re doing all that in parallel,” Moran says. “We’re not waiting for next-generation or a complete redesign which will take quite a bit longer we’re installing some mitigation measures.”

Meanwhile, the Navy is sharing its findings on hypoxia issues with the US Air Force, which recently experienced oxygen problems on Lockheed Martin F-35As at Luke Air Force Base, Arizona. The Defense Department has asked the navy for information on the hypoxia study and will determine whether the F-35 effort should merit an independent or can follow on the navy’s effort, Moran says.