It was a proud moment for the Edwards community when Air Combat Command announced the F-22 Raptor had resumed normal flight operations April 4, particularly for the F-22 Combined Test Force and 412th Aerospace Medicine Squadron, which played vital roles in the jet’s full-force return.
In May 2011 Defense Secretary Leon Panetta stood down the fleet for a period of four months. In September of 2011 the F-22 fleet returned to flying operations with a list of restrictions intended to mitigate risks while personnel worked towards identifying root causes and finding solutions to eliminate hypoxia-like symptoms reported by Raptor pilots.
“The public, Congress and media were all eager to get answers as soon as possible, but we had to perform root-cause analysis in a methodical way to make sure that no stone was left unturned. We did not want to jump to conclusions prematurely,” said Lt. Col. Daron Drown, F-22 CTF director.
In January 2012 the Secretary of the Air Force directed the creation of the F-22 Life Support System Task Force led by the Air Combat Command director of operations. Along with the F-22 System Program Office, Edwards personnel joined forces with leading experts from the U.S. Navy, Air Force Research Laboratory, NASA, Lockheed Martin and Boeing as part of the Task Force.
The Task Force conducted root-cause analysis of the life support system anomaly, ultimately determining that the culprit was restriction to the pilot’s breathing, not insufficient oxygen output from the aircraft or a contamination of the oxygen supply.
“All of our jets were used for data collection,” said Drown. “In addition to our aircraft, we instrumented and evaluated an F-22 from Joint Base Langley-Eustis, Va., and another from Joint Base Elmendorf-Richardson, Alaska, to check for any contamination. We also used sensors to monitor our pilots. We collected data from about 150 sorties using a variety of sensors, some of them routinely used in hospitals.”
Sensors analyzed oxygen concentration, volatile organic compounds, as well as other potential contaminants, providing the test team with real-time data.
“We put sensors in the airplane to measure oxygen concentration and look for contaminants. We also put some sensors in the mask to see how much carbon dioxide pilots were breathing off,” said Lt. Col. Kathy Hughes, 412th AMDS commander. “For pilots, there were blood tests, lung function tests, and we checked for toxins. Pulse oximeters were also used to check the oxygen saturation of their blood.”
It was a unique challenge for the F-22 CTF to become familiar with medical sensors not typically used during flight test.
The pulse oximeter, for example, was originally worn on the pilot’s finger, but consistent interference proved to be problematic.
The sensor had to be moved, and it was 1st Lt. Carolyn Price from the 412th AMDS who determined mounting it to the pilot’s earcup would not only provide the F-22 CTF with more accurate data but create less of a hindrance to the pilot.
Data gathered during flight and ground test produced interesting results and revealed the root-causes of the hypoxia-like symptoms pilots had been experiencing.
The upper pressure garment vests donned by Raptor pilots to protect them in the event of rapid cockpit decompression at high altitudes were inflating prematurely, while deflation was delayed.
“You need space for lungs to expand and contract. It’s just as important to get oxygen into your system as it is to expel carbon dioxide. Lungs have to effectively get carbon dioxide out. For pilots wearing the vest, the bottom of their lungs were being squeezed and it is hypothesized that they could not effectively exchange carbon dioxide and oxygen,” said Drown.
The upper pressure garment’s valve was therefore redesigned and tested by the F-22 CTF before being distributed throughout the fleet.
“The new vest valve prevents premature inflation of the vest and allows it to deflate more rapidly,” said Drown. “This gives pilots more room for their lungs to expand following high-G maneuvering. The new valve was fielded January 10, and operational pilots have given it the thumbs up.”
In addition to the work done to redesign and test the new valve, Edwards personnel also facilitated other modifications to the F-22s life support system that enhanced the aircraft’s margin of safety. One such improvement was the addition of an Automatic Backup Oxygen System to replace use of the F-22′s original Emergency Oxygen System in the event of interruption to the breathing air supply.
Earlier this year, the F-22 CTF began installing the ABOS, a process that will continue through 2014 across the entire fleet. Pilots equipped with ABOS no longer have to activate their emergency oxygen supply. In the event of aircraft malfunctions that interrupt the pilot’s primary supply of breathing air, the new ABOS system automatically turns on, reducing the complexity of dealing with the failure.
“It’s been a challenge, but the Raptor is finally back flying where it is most effective. I’m very proud of the team, as lessons we learned from this will not only benefit the F-22 and keep our pilots safe, but other aircraft programs will benefit as well,” said Drown.
For Hughes, work completed by the F-22 Life Support System Task Force emphasizes the need for continual research in aerospace physiology.
“What happened with the F-22 reinvigorated the Air Force and Department of Defense’s need for continual research in aerospace physiology, particularly concerning flight crew equipment,” she said. “Aircrew safety is a top priority; it’s important that we continue our research.”