Four US F/A-18 Pilot Deaths Tied to Oxygen System Issues

An investigation was launched in late March after more than 100 T-45 instructor pilots at a number of US Navy training bases refused to fly with students in trainer jets to protest against the ongoing issue with oxygen contamination that can result in disorientation, loss of consciousness and even death.

Due to the increase in cases of hypoxia caused by problems with the Onboard Oxygen Generation System (OBOGS), US Navy student pilots have not been allowed to fly for the past three months.

On Thursday, the Navy released a report on the ongoing investigation development. The investigators have documented a rise in T-45 oxygen system failures from 13 in 2012 to 38 in 2016. Hornet oxygen system failures have also spiked from 57 to 125 during the same period.

Investigators suggest that the deaths of four F-18 pilots that occurred over more than a decade could be attributed to the quality of air in the cockpit, for all incidents were linked by the fact that pilots experienced symptoms falling within the scope of what is described as a "physiological episode" in response to hypoxia.

"Subsequent to these mishaps, training to recognize the symptoms increased and procedures now stress the importance of selecting emergency oxygen as a first step. Correct application of emergency oxygen would have likely prevented these mishaps," the investigation reported.

A single root cause of the problems has not been discovered, but the Navy managed to identify several areas of concern. For instance, pilots on both T-45 and F-18 breathe through OBOGS that use a sieve to absorb excess nitrogen from the air and add oxygen into the mixture before passing it on to the pilot.

But the sieve is highly sensitive to temperature changes and humidity and can be affected by water to the point that "any entrapped contaminants could be exchanged for moisture in the sieve bed and the contaminants then released from OBOGS into aircrew breathing air," the report says.

The Navy said it now intends to look at all the oxygen system components on its jets. Both aircraft are in the process of getting new, upgraded sieve systems.