Under the heading "Impact If Not Fixed," the test group member wrote, "Real-world failure of [the oxygen system] due to ECS shutdown is unacceptable. ECS failure and the subsequent loss of supplemental breathing oxygen may result in pilot debilitation or fatality due to either altitude hypoxia [oxygen deprivation] or decompression sickness in the event of cabin depressurization."
"Investigate and take corrective action," the 2000 document says. "Suggest repairing the ECS system so it will provide continuous, adequate service throughout the flight envelope. Suggest providing a reliable source of bleed air for [the oxygen system] in the event of ECS failure... [C]onsider addition of pilot breathing air plenum to fill gaps when [the oxygen system] is not operating, as during ECS shutdown."
A plenum, as described by former Marine Corps fighter pilot and ABC News consultant Steve Ganyard, is a common feature in legacy fighter planes akin to a tank within the primary oxygen system that could hold excess air for use in the case of crisis.
The Air Force was able to "mitigate" the instances of ECS shut down due to the high-altitude maneuvers to "an acceptable level of operational risk," the service said, but it never provided a secondary "reliable source" of air for the oxygen system nor did it add a plenum as a back-up. Instead, the Air Force directed pilots to a manual emergency oxygen system in the event of an ECS shutdown.
Here is an excerpt from an earlier story I did that covers the USAF's efforts to upgrade the Raptor. The full story can found here.
In 2014, the USAF will start to field Increment 3.2A. The software-only modification "incorporates new electronic protection techniques and improves the situational awareness of the pilot with the addition of new combat identification techniques", Williams says. It will also correlate data from the Link 16 data-link and fuse it with the F-22's integrated sensors.
That effort will be followed up with an Increment 3.2B upgrade. A Milestone B decision to go ahead with the procurement of Increment 3.2B is planned for December 2012, Williams says. "Kit procurement begins in fiscal year  with kit deliveries in [the third quarter of] fiscal year  and initial installations completed in [the first quarter of fiscal year ," he says.
Increment 3.2B is a hardware and software upgrade that will fully incorporate the
AIM-120D and AIM-9X air-to-air missiles in addition to further upgraded geo-location and electronic protection capabilities.
But according to a recent Government Accountability Office (GAO) report, it will no longer add the capability to independently re-target eight SDBs at eight separate targets or an automatic ground collision avoidance system (Auto-GCAS). A USAF Scientific Advisory Board study on the Raptor's ongoing oxygen system woes has recommended that an Auto-GCAS be implemented.
Increment 3.2B is a much more complicated upgrade than the previous efforts.
"We will be implementing a new enhanced stores management system, increasing the ability of the aircraft to communicate with the weapons," Williams says. "This change will provide a common split-bus architecture for the Block 30/35 aircraft to support the increased communication requirements of newer weapon systems."
However, the USAF cannot wait until 2017 to launch its newest air-to-air weapons from the Raptor. The service is planning to add a "rudimentary" capability to carry both the AIM-9X and AIM-120D before Increment 3.2B is completed.
The AIM-120D will be added first in Update 4, which the service plans to release to the fleet in 2013. The AIM-9X will be added in Update 5, which is set for a 2015 release. "The AIM-9X effort in Update 5 also serves as a risk reduction activity for Increment 3.2B," Williams says.
Every aircraft from Tail 03-4045 onwards will receive Increment 3.2A and B, says ACC. According to a recent Government Accountability Office report, the cost of the Raptor upgrade programme will total about $9.7 billion.
A further update called Increment 3.2C has recently been renamed Increment 3.3, but the capabilities that it might include have not yet been defined. Williams says it will focus on making sure the Raptor remains compatible with new air traffic control systems.
"The effort will be focused on maintaining airspace access and endeavour to include all of the current airspace mandates like Mode S and Mode 5 as well as other FAA/ICAO mandated requirements," he says.
The F-22 System Program Office is still working on trying to graft an open systems architecture to the jet's computers.
Meanwhile, the Flight defense team is in Las Vegas, Nevada, for AVUSI's Unmanned Systems North America 2012 show. So watch for our coverage.