Back in April, the US Navy (USN) grounded all of its T-45 training flights due to issues with the cockpit oxygen system. I personally heard about this before the grounding secondhand from someone in the program, who was familiar with an instructor who did not remember landing during a training flight.
A number of questions arise, but in order to keep with the single question style that seems to be preferred on this board, I will limit myself to one:
Why is it not practical for USN T-45 trainers to be fitted with oxygen systems used in other trainers?
The T-6 Texan II, used in the USN Primary Pilot training phase uses an onboard oxygen-generating system (OBOGS). I would assume that the US Air Force jet trainer uses one as well. It surprises me that with a problem that has spanned several years and with a program that has been grounded for three months (and counting) and no solution on the horizon, such alternatives are not being considered.