Former President Jimmy Carter has been hospitalized for observation after developing an upset stomach while on a flight to Cleveland, The Associated Press reported.

Carter, the 39th President of the United States, penned a new book titled “White House Diary” and was on the way to a book signing scheduled for 1 p.m. in Cleveland when he suddenly fell ill, a representative for the Carter Center said.

Jackie Mayo, a spokeswoman at Cleveland Hopkins International Airport, confirmed that Carter, 85, was a passenger on a Delta flight to Cleveland late Tuesday morning when he removed from the flight by rescue crews and transported to MetroHealth Hospital after becoming ill.