In early April, the Navy announced an operational pause for all its T-45s at the three training bases that fly them. The move came after about 100 instructor pilots refused to fly, citing safety concerns with the aircraft amid a surge of hypoxia-like incidents in the cockpit, according to a report from Fox News.

Later the same month, the aircraft resumed operations with stringent flight limitations, include a 5,000-foot altitude limit and a requirement that pilots pull no more than 2Gs. But training flights for student pilots remained effectively halted, with only currency flights for trainers taking place. That was still the case as of mid-June, Vice Adm. Paul Grosklags, head of Naval Air Systems command, told lawmakers during a hearing on naval aviation.

Since then, a series of measures have been implemented to gauge cockpit safety and improve systems in the trainers, including installation of the CRU-123 oxygen monitor system, an upgrade from the CRU-99 system that allows for measurement of oxygen and has the capacity to download data on cockpit conditions after each flight. As of Sept. 14, 111 of the 170 T-45s have been outfitted with the systems, Lt. Cmdr. Dave Bennett, a spokesman for the Navy’s physiological episodes action team, told Military.com.

“We assess that all T-45 aircraft will have the CRU-123 installed by the end of the second quarter of 2018,” he said.

Capt. Sara “Clutch” Joyner, the newly appointed head of the Navy’s team to study physiological episodes, said additional mitigating measures have included instruments that more precisely measure oxygen, air pressure, and any air contaminants.

“So NAVAIR was able to come up with a monitoring system and we were able to adjust fleet procedures or training procedures so they were able to stay in the regimes of flight that were most supportive,” she said. “And we were able to groom the aircraft as well to make sure they were keeping that work of breathing to a supportable level for the human being.”

New episodes

Since those measures were implemented in August, however, about four additional cockpit episodes have been documented. These episodes, Joyner said, share a telling commonality: in the two-seater aircraft, one of the aircrew experienced problems, and the other did not. In addition, she said, measurement devices reported that oxygen and air pressure remained at normal levels.

“When we went through, we were able to really review and find human factors and also physiological responses when people are under stress and how they breathe. And we’re working right now to make sure we’re incorporating that training as well for the aviators,” Joyner said. “So I would say more of what we’ve seen to date has been physiologically based response, but the aircraft overall has seemed to be well supporting the human in the loop.”

In addition, she said, new measurement devices have yet to find any evidence of cockpit air contaminants that would present a concern for aircrew.

With recent incidents, Joyner said, evidence points to the human rather than the machine as the source of the issue.

‘No Fixing the Human’

For those on the Navy’s team to diagnose and fix physiological episodes, the determination that human factors are sometimes the source presents its own levels of complexity.

“There is no fixing the human; there is nothing broken with the human,” said Capt. Cliff Blumenberg, the Navy’s Aerospace Medicine branch head and director for Fleet Programs. “Every human reacts differently to every situation. The same person in the same aircraft on different days and different flights might experience a physiological episode on one flight and maybe not on the next.”

Possible factors affecting whether an episode is experienced, he said, might include hydration levels, rest, onset of sickness, and even emotions and stressors.

“[It could be] any unanticipated physical response that impacts your ability to pilot that aircraft,” Blumenberg said. “Some may be due to pressure performance and some of it may be due to something else. Some may be a combination of the two.”

The Navy announced in May that it was substituting a portable reduced oxygen breathing device, or ROBD, in place of its large low-pressure chambers historically used for aviation hypoxia training. The move makes training more realistic, officials said at the time, and reduces the risk of decompression sickness inherent in the old trainers.

Officials said the training now emphasizes participation from other members of the squadron, unaffected by limited on oxygen flow.

“So now I’m not only training myself to recognize symptoms in me, but I’m training my wingmen to recognize symptoms in me, so [they know] how to recognize it early and take action quickly,” said Capt. David “DW” Kindley, F/A-18 and EA-18G program office manager for the Navy.

Efforts continue to pinpoint the cause of the surge in cockpit episodes affecting the T-45, as well as causes of hypoxia-like episodes in the F/A-18 Hornet. But as officials probe both human and mechanical factors contributing to problems in the air, it appears one outcome of the Navy’s assessment may be a more cautious approach to entering the cockpit in the first place.

“Maybe there are times when they shouldn’t go in a jet and they can self-recognize before they take off the ground that this is not the day for them to go airborne,” Joyner said. “It’s sort of a dual approach.”