On the night of 27 December 1972, during Operation Linebacker II (also referred to as the Christmas Bombings), then-Major Phạm engaged a USAF Strategic Air Command (SAC) B-52 Stratofortress heavy bomber using air-to-air missiles. He reported that his missiles struck the B-52, causing it to go down in flames. This claim, which would be the only B-52 downed in aerial combat, is disputed by U.S. records, which state that this B-52 was downed by a surface-to-air missile, also responsible for all other B-52s shot down during the campaign. In a book named "Hà Nội - Điện Biên Phủ trên không" (Hanoi - the Battle of Dien Bien Phu in the air) by Nguyễn Minh Tâm, published by Nhà xuất bản Quân đội Nhân dân Việt Nam (Viet Nam People's Army Publishing House), the author affirms that Phạm Tuân shot down the B-52 with two K-13 air-to-air missiles within a range of 4 kilometers.