Has the USAF solved T-6 hypoxia problems?

A number of incidents at Vance Air Force base were among the first in a series of hypoxic and hypoxic-like episodes that plagued the T-6 fleet, that led to the USAF looking to remedy the issue. Five pilots at Vance reported hypoxia-like symptoms during four flights, leading to the November 2017 grounding for three weeks.

The Beechcraft T-6 Texan II is a single-engine turboprop aircraft built by the Raytheon Aircraft Company. It is a trainer aircraft based on the Pilatus PC-9. The Hellenic Air Force operates 25 T-6A and 20 T-6A NTA aircraft.

Concerns began to mount, and frustrations grew, as such episodes continued without a solution. In January 2018, the 19th Air Force suspended all T-6 solo flights and authorized pilots to fly with their masks down to reduce risks of hypoxia. After the wave of physiological episodes the last week of that month, the US Air Force grounded all T-6 flights for all of February and launched a serious effort to figure out what was wrong.

In early February 2018, Rep. Michael Turner, R-Ohio attacked Lieutenant General Mark Nowland, then-deputy chief of staff for operations, for suggesting that training would be an important part of fixing the problem, implying that it was the fault of pilots rather than the Air Force. Nowland swiftly clarified he was not blaming pilots.

After months of study, the Air Force concluded that the physiological episodes were caused by rapidly fluctuating oxygen concentrations in the T-6. It wasn’t happening all the time, or even most of the time, which made the problem tricky to pinpoint.

One thing the Air Force learned from consulting with the Navy is that periodically purging moisture from the On-Board Oxygen Generating System OBOGS — as the Navy does every two weeks — might cut down on unexplained physiological event (UPEs). Some maintainers and experts from the Air Force Research Laboratory believe the buildup of moisture degrades the OBOGS’ performance.

The Air Force has been purging moisture regularly for the past few months, and there are signs that it’s helping. The Air Force is also experimenting with moisture purges at different intervals to see which is most effective.

The Air Force is also in the midst of some long-overdue hardware upgrades to the T-6’s OBOGS. A new oxygen concentrator has been designed, and deliveries began in December. The redesigned concentrator has new parts and materials, is built to more recent specifications, and is more reliable than the previous two-decade-old concentrator, he said. It will likely take a year to 18 months to install the new concentrators in all of the roughly 400 T-6s in the fleet.

One of the new concentrator’s biggest improvements is that its software can be easily upgraded or adjusted if, for example, the Air Force decides to tweak the concentration of oxygen in the cockpit. This is similar to how engine software is upgraded today.

The old concentrator wasn’t designed to accept software adjustments, so maintainers would have to physically take the concentrator out of the plane and basically “break” the device to hack in the new software.

The Air Force is designing a backup system for the T-6, similar to the F-15’s which now has a two-tank OBOGS, and a prototype is expected to be ready in a year, however, it’s not certain the Air Force will move forward with the four-tank OBOGS for the T-6.

The T-6 will also get more sensors to better track how oxygen is flowing to the pilot. The T-6 OBOGS currently has sensors that measure whether it’s producing oxygen, how much, and if the system is meeting its requirements. But it doesn’t have sensors that show if the oxygen is flowing all the way to the pilot’s mask and regulator, like the Strike Eagle does, which could alert the pilot if there’s a leak in a hose or other problem.

The T-6 OBOGS will be almost entirely replaced, save for a few standard pipes and hoses. The oxygen concentrator upgrade alone accounts for 80 percent of the OBOGS.