(CNN) The late former president George H.W. Bush's final flights on Air Force One will be called "Special Mission 41," Bush's spokesman said Sunday.

By tradition, the plane is only called Air Force One when the president is on board. President Donald Trump will not be traveling on the aircraft, so the plane has been redesignated and renamed to honor Bush this week.

"Air Force One has arrived in Houston for what will technically be called 'Special Air Mission 41' tomorrow and Wednesday. A beautiful day in Texas -- 'ceiling and visibility unlimited,' Mr. President," Jim McGrath tweeted.

Air Force One has arrived in Houston for what will technically be called "Special Air Mission 41" tomorrow and Wednesday. A beautiful day In Texas -- "ceiling and visibility unlimited," Mr. President. #Remembering41 #CAVU pic.twitter.com/F1xWzDxd04 — Jim McGrath (@jgm41) December 2, 2018

The "ceiling and visibility unlimited" phrase is from Bush's time in the Navy. Bush had a plaque with the acronym "CAVU" mounted on the wall of his home in Kennebunkport, Maine. In 2001, he wrote a letter to his children, that reads, "C-A-V-U was the kind of weather we Navy pilots wanted when we were to fly off our carrier in the Pacific -- 'Ceiling and Visibility Unlimited.'"

When Bush's family and friends shared the news of his death at the age of 94 on Friday, they used the code word "CAVU."

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