A Joint Strike Fighter F-35 flies during the Avalon Airshow. Photo: Scott Barbour/ Getty Images.

Australia’s F-35 stealth fighter jets have been grounded after pilots were experiencing oxygen deprivation while flying.

The US Air Force has ordered a flight ban at its base in Arizona, where four Australian pilots are among the 55 currently training, while investigations are under way.

Since May, there have reportedly been five incidents of hypoxia or oxygen deprivation.

The US Air Force told Fairfax Media the incidents were not considered serious and backup oxygen systems were implemented.

As part of Australia’s Joint Strike Fighter program, the government is buying 72 F-35A Lightning IIs at a cost of $17.1 billion.

To date the program has experienced a number of delays and cost blowouts, meaning the first F-35s won’t arrive in Australia until late 2018 before entering service in 2020.

The first two of Australia’s F-35s debuted at the Australian International Airshow at Avalon, Victoria, in March. Read more on that here.

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