The U.S. Air Force’s new VC-25B “Bridge” aircraft made its international debut on July 8, flying President Donald Trump abroad, but for only part of the trip.

Trump flew on the new Boeing 747-8i Air Force One from Joint Base Andrews, Maryland, to Ankara, Turkey, but left on the legacy VC-25A. In a social media post, Trump said the VC-25B returned to RAF Mildenhall, England, to give military personnel the chance to tour the aircraft. He later said in a press conference that he would fly back from Turkey via “normal means," and then boarded the VC-25B Bridge in Mildenhall to return to Andrews.

The split itinerary highlights potential differences between the long-serving VC-25As and the new aircraft, which was rapidly modified after being gifted by the government of Qatar last year. L3Harris quickly refurbished the airframe at a cost of about $400 million. The Air Force in an announcement said the approach omitted “some of the less commonly used mission sets” that Boeing needs to install on the next two VC-25Bs.

These could be connected to self-defense systems on the aircraft and other highly sensitive communication equipment needed to protect the president, particularly in airspace in and around Turkey. Trump’s visit to Ankara for the NATO summit comes amid heightened tensions as the U.S. has resumed airstrikes on Iran.

The day before the trip, 13 Democratic senators sent a letter to Air Force Secretary Troy Meink and L3Harris CEO Chris Kubasik about the aircraft, raising concerns about the “rushed” retrofit.

“For over a year, the administration has stonewalled congressional requests for information about Qatar’s luxury jet gift to President Trump,” the letter states. “Congress and the American public have expressed due outrage about this corrupt, illegal exchange, but Pentagon officials have mostly deflected questions or claimed inability to share classified details about the luxury jet, the memorandum of understanding with Qatar and the program to modify it for use by the President.”