BEIRUT – A Syrian fighter pilot on a training mission flew his MiG-21 warplane to neighboring Jordan, where he was given asylum Thursday in a defection from the fiercely loyal air force, signaling that some of the most ironclad allegiances in Damascus could be fraying. Syria immediately denounced the pilot as a traitor.

The brazen move was a clear triumph for the rebels fighting to overthrow President Bashar Assad and was the first defection by an air force officer with his plane since the uprising began in March 2011.

The pilot, identified as Col. Hassan Hammadeh, removed his air force tag and knelt on the tarmac in prayer after landing at King Hussein Air Base in Mafraq, Jordan, 45 miles north of Amman, a Jordanian security official said.