The U.S. Air Force's fleet of stealthy F-22 Raptor fifth-generation fighters has suffered two additional "physiological incidents" since Nov. 21, the service confirmed Dec. 2.
"Since 21 Nov., there have been two physiological incidents and no events of interest," said Air Combat Command spokeswoman Kelly Sanders in an emailed statement.
Since the F-22 returned to flight in September after a four-month grounding, the Air Force has maintained two listings for problems arising from operating the jet. The jet was originally grounded in May after more than a dozen pilots suffered symptoms resembling hypoxia.
"Under the current protocols established to monitor F-22 operations since their return to flight, occurrences are categorized into events of interest and physiological incidents," Sanders wrote. "An event of interest is an aircraft indication, system malfunction or a data point that has not caused symptoms of hypoxia nor caused any danger to the pilot or aircraft, but is noteworthy for data collection and further analysis."
However, because of the Raptor's unresolved oxygen system problems, a separate category has been established for incidents that resemble hypoxia.
"Any event of hypoxia or hypoxia-like symptoms during pre-flight activities or a mission would be categorized by Air Force Instructions as a physiological incident," Sanders wrote.
She noted that none of the most recent incidents caused any damage. Air Force sources who tipped off Defense News to these events had alluded to ground crews becoming ill when performing maintenance operations with the engines running. An Air Force official confirmed that was the case with a separate incident. However, the two most recent cases Air Combat Command referred to happened in the air.
"None of these incidents resulted in harm to a person or aircraft," Sanders wrote. "There is a rigorous process of collecting and analyzing operational, maintenance, and physiological data relevant to any incidents, which typically takes several weeks to complete and may or may not produce actionable information."