Thursday, September 13, 2018

Varying oxygen levels in cockpit sickened pilots, Air Force says



The Air Force training command said Thursday that a problem with varying levels of oxygen concentrations in the cockpit was identified as the major factor in unexplained physiological events that have sickened dozens of T-6 Texan II pilots this year.

The San Antonio-based command, which has investigated malfunctions in its onboard oxygen generation system since it grounded the T-6 in February, also revealed how it plans to fix the problem.

“So far, technical efforts to date and analysis of data collected have determined that pilots have been exposed to significantly changing levels of oxygen concentration,” Lt. Gen. Steve Kwast, head of the training command, said in a statement Thursday afternoon.

He said the system sometimes was producing more oxygen than a pilot needs, which caused problems for some aviators.

Problems with the onboard oxygen generation system, or OBOGS, on the training plane had prompted as many as 11 pilots with the 12th Flying Training Wing to refuse to fly the aircraft. They took the action after aviators had suffered unexplained physiological episodes — called UPEs by the Air Force — that can incapacitate pilots and even lead to their deaths.

Gen. David Goldfein, the Air Force chief of staff, recently told the San Antonio Express-News that investigators had found the root cause of the problem and would begin making fixes.

Kwast said symptoms experienced by some of the pilots were similar to a lack of oxygen, lack of carbon dioxide or other related conditions.

The Air Force Materiel Command created an independent review team to investigate the problems. Investigators learned that the OBOGS filter and drain valves failed at a much higher than anticipated rate. These parts were repaired or replaced.

The Air Force has said that the OBOGS shutoff valve, which funnels air from the engine into the system, failed at a much higher rate than expected. Inspections showed that 85 percent of the shutoff valves inspected failed in the open position, allowing unrestricted air flow. Investigators also found that the same percentage of inlet filters had evidence of moisture but with no significant effect to airflow.

Given that some oxygen system components failed at higher than expected rates, the T-6 Program Office on Tinker AFB, Oklahoma, directed inspections on a more aggressive timeline. Maj. Gen. Patrick Doherty, commander of the 19th Air Force, said that purging excess moisture from the system appears to keep the OBOGS operating more efficiently over time.

Texan II pilots, meanwhile, have been given extra training and procedures to help them respond to possible oxygen system malfunctions. The training command will add study materials for T-6 aviaiors that will focus on identifying symptoms, responses and corrective procedures for all types of events, not just hypoxia.

More fixes are on the way as well. The Air Force has started a redesign of the T-6 OBOGS system to stabilize the variation in oxygen levels pilots breathe — a process likely to take from two to four years. Experts also are working with the plane’s manufacturer to adjust the OBOGS software algorithm to stabilize oxygen concentrations.

The Air Force said those measures should reduce physiological events, but more will be done, including a broader redesign. New maintenance procedures drawn from several different Air Force and Navy T-6 bases also will be introduced.

Brig. Gen. Edward L. Vaughan, who leads the Air Force Physiological Episodes Action Team, will collaborate with Air Force officials and other military branches to determine if the OBOGS measures planned for the T-6 will be applicable across other aircraft that use the oxygen system.

The OBOGS failures resulted in at least 61 reported unexplained physiological episodes during the first six months of this year. The Texan II resumed flight in March as the Air Force announced a more frequent cleaning, testing and maintenance schedule for the oxygen system while the search for a root cause ensued.

The Navy grounded its T-45 Goshawk, a jet trainer, after pilots suffered similar physiological episodes. Hypoxia, a lack of oxygen that is potentially fatal, was suspected when an instructor pilot and student bailed out of a T-45 from Naval Air Station Kingsville that crashed Aug. 14, 2016.

Other possible causes of UPEs involve hypocapnia, a state of reduced carbon dioxide in the blood, and hypercapnia, excessive carbon dioxide in the blood, usually caused by inadequate respiration.

The T-6A grounding came after 22 physiological episodes were recorded in January, the most ever seen in the single-engine, two-seat turboprop since it was introduced in 2000. The training command declared it safe.

Pilots harbored doubts and complained that months of investigation by the Air Force, Navy and NASA had yet to explain why the system failed or how it would be fixed. Some argued that they were not told about the severity of reported physiological episodes.

The Air Force, though, has said it is keeping pilots in the loop.

“Since our T-6 operational pause, we have made every effort to communicate with every instructor and every student exactly what we’ve found,” Doherty, the 19th Air Force commander, said in the statement Thursday. “Transparency remains of utmost importance to use as we all work together to ensure that our pilots are safe and know the way ahead.”

Original article can be found here ➤ https://www.expressnews.com

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