The US Air Force has grounded a fleet of F-35 fighter jets indefinitely over concerns over pilots' oxygen supplies, according to a spokesman.
F-35 air operations were paused at an Arizona air base after pilots suffered symptoms resembling hypoxia, or oxygen deprivation, Captain Mark Graff said.
Lockheed Martin, which built the jet, said it still plans to show the plane at the Paris Air Show this month.
Air Force officials said F-35 fighter jets at other bases were still in use.
Luke Air Force Base, located northwest of Phoenix, cancelled local flying operations for its F-35A Lightning II aircraft on Friday after five incidents were reported in which pilots experienced hypoxia-like symptoms.
But they continued to be grounded on Monday as the Air Force investigated the issue with pilots, maintenance workers and medical professionals, according to base spokeswoman Major Rebecca Heyse.
The incidents took place between 2 May and Thursday, but in each case the jet's backup oxygen system was successful and the aircraft landed safely.
Luke Air Force Base has 55 F-35A Lightning II jets in operation and conducts 25 training flights each weekday, according to base officials.
More than 220 operational F-35 jets have been built worldwide. The stealthy jets have logged more than 95,000 flight hours, but the planes have yet to see combat.