Why Are F-22 Pilots Choking?

Wired:

Also on Tuesday, Warner and Rep. Adam Kinzinger (R-Illinois) sent a letter to Air Force officials that cited data from an Air Force committee about a crucial Raptor component, the On-Board Oxygen Generating System, or OBOGS. The data indicates that the “quantity of oxygen” the pilots need “may, in fact, be greater” than what the OBOGS supplies. And Warner wants to know whether the data will reach a panel in charge of overseeing the investigation.

“I have to say at least I have concerns about the Air Force’s ability to get to the bottom of this,” Warner said.
OBOGS had long been suspected as a culprit. The way it works: Compressed air from the Raptor’s engines is sucked into the system, which produces a (theoretically) unlimited supply of breathable oxygen. If there’s a problem with getting enough oxygen, odds are there’s a problem with OBOGS.
But in February, attention focused on the F-22′s coolant system, which investigators believed could be leaking into the oxygen system. Another potential culprit was the pilots’ constrictive g-suits, which the Air Force ordered replaced. But with incidents still occurring, attention refocused on OBOGS.
“One of the things that the Air Force had indicated to us was that they were looking at the fact that the OBOGS, when it was originally designed, may have been designed to older standards of how many liters of oxygen per minute a pilot needed,” Warner said. “And that when you actually look at the extremely high workloads these pilots are enduring under high gees, heavy maneuvering type of flight, that it may be that they require more oxygen than the system was originally designed to put out.”
But that wouldn’t explain hypoxia-like incidents which occurred on the ground, Warner cautions. The truth may instead be a series of interrelated problems with no easy solution. Even attempting to fix the problem has created other problems.

Wow.  This would seem like something the Air Force would have under control.  Pilots have been provided oxygen since we were flying B-17s.  I can't believe they haven't been able to figure out what is causing it.