Secretary of State Antony Blinken was forced to switch planes in Switzerland on Wednesday after his plane was grounded due to a critical failure related to an oxygen leak.

Blinken and fellow passengers boarded one of Boeing’s popular 737 commercial jets used by the U.S. military, a Boeing C-40. It differs from the Max 9 airplanes that are being audited for safety problems by the Federal Aviation Administration after a door plug blew off an Alaska Airlines flight in midair more than a week ago. 

Blinken was attending the World Economic Forum’s annual meeting in the Swiss ski resort of Davos this week. He was transported out of Davos on a helicopter for Zurich and boarded the Boeing 737 before being told the aircraft was unsafe to fly due to an unfixable oxygen leak.

The Boeing C-40 is a modified business model of the Boeing 737-700, operated by the U.S. Air Force out of Joint Base Andrews in Maryland. The aircraft is used to transport members of the Cabinet and Congress, according to the Air Force. 

A new plane was arranged for Blinken while aides and the press pool traveling with him flew back to the U.S. on commercial flights, according to Bloomberg. 

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The FAA said its investigation into the Boeing 737 MAX 9 planes will continue, and investigators have yet to determine the exact reason a portion of the plane’s fuselage on Alaska Airlines flight 1282 flew off shortly after departing from Portland, Oregon. Passengers and crew touched down safely after an emergency landing at the departed airport, but there were some injuries, and several passengers are suing Boeing for damages. 

“All 737-9 MAX aircraft with door plugs will remain grounded pending the FAA’s review and final approval of an inspection and maintenance process that satisfies all FAA safety requirements,” the FAA said in a statement.