Two of the three episodes occurred in November in the air, during flights out of Davis-Monthan Air Force Base, Arizona, according to Air Force spokesman Capt. Josh Benedetti. In both cases the A-10's backup oxygen system kicked in allowing the pilots to return safely to base. A third pilot suffered from hypoxia symptoms while he was still on the ground.
The root cause of the incident that took place in the sole aircraft outfitted with the older liquid oxygen system (LOX) was later successfully diagnosed and fixed — the Warthog had issues with the oxygen regulator and cabin pressure systems. But investigators haven't yet determined the cause of the problem on the aircraft equipped with the newer Onboard Oxygen Generation System (OBOGS).
The whole fleet of 28 OBOGS-equipped A-10s assigned to Davis-Monathan had to be grounded for about a week, Aviation Week & Space Technology reported.
Root causes of many of these incidents remain unsolved; they can vary from engines to the oxygen-generating capability of the aircraft itself.