We received a briefing this morning on this, and I think it did a lot to dispel some of the complaints voiced in this thread. For the last month, an OT&E team has been flying sorties breathing ambient air and undergoing endless medical analysis before and after each flight, NASA has been involved sampling cockpit and mask air quality, and maintenance has been tearing down OBOGS to try and find a source of the issue. Below are some of the highlights from that briefing.
1) Only TCTO compliant aircraft will be flown with OBOGS operational as normal. Breathing cockpit air was not approved by AETC nor recommended by the OT&E team. To answer those who wondered why this was such a big deal when other aircraft fly unpressurized without oxygen, it is an FAA airworthiness certificate issue. Without the OBOGS, the T-6 would not be considered airworthy by the FAA without an amendment.
2) The TCTOs are a "millimeter by millimeter" (their words) inspection of the OBOGS from the engine air inlet all the way to the mask. It replaces parts to make the system as close to factory new as possible.
3) This is not the end. No causal factor was found, but the OT&E unanimously agreed that returning the OBOGS to a factory new state made them comfortable flying the jet. Flying is still volunteer only at PIT.
4) The top six of the T-6 SPO were fired due to mismanagement of the program and a fly-to-fail mentality. The zeolite bed maintenance interval has been aggressively reduced from 4,500 to 700 hours, and the new SPO is re-evaluating other fly-to-fail parts on the T-6 to possibly set replacement intervals. 19 AF is also using this debacle to highlight the ISS and EFIS issues.
5) The future: The team considers this only the beginning and are still trying to drill down to a single cause. From what the briefer said though, the OBOGS on all of the jets inspected were absolutely horrendous (kinked lines, valves stuck in the open position, evidence of water in the lines, general dirt and gunk, etc), and 79% failed the inspection, so there might not be one silver bullet. The incident T-6s are all still impounded, but an Edwards AFB test team will begin inspecting those independently and in parallel so the two teams can compare notes.
Honestly, I was pretty impressed with what the team has been doing this last month. There were a lot of really smart people helping with this, to include a NASA test engineer who has made a career out of OBOGS issues. It also received visibility all the way up to the VPOTUS. My biggest misgiving is that they never found a single causal factor, but I am not surprised given the fact that the entire system was basically never inspected since the plane left the factory. I think the 19 AF initially fumbled at the beginning of this grounding a month ago, but since then a lot of good things have happened to make up for it.