Iron Eagle

Doug Masters, son of veteran U.S. Air Force pilot Col. Ted Masters, is a hotshot civilian pilot, hoping to follow in his father's footsteps. His hopes are dashed when he receives a notice of rejection from the Air Force Academy. Making matters worse is the news that his father has been shot down and captured by the fictional Arab state of Bilya while patrolling over the Mediterranean Sea. Despite the incident occurring over international waters, the Arab state's court finds Col. Masters guilty of trespassing over their territory and sentences him to hang in three days. Seeing that the U.S. government will do nothing to save his father's life, Doug decides to take matters into his own hands and come up with his own rescue mission. He requests the help of Col. Charles "Chappy" Sinclair, a Vietnam veteran pilot currently in the Air Force Reserve, who, while not knowing Col. Masters personally, had a favorable run-in with him years prior to meeting Doug and "knew the type." Chappy is skeptical at first; but Doug convinces him that, with his friends, he has full access to the airbase's intelligence and resources and can give him an F-16 fighter for the mission. To Doug's surprise, Chappy had already begun planning a rescue operation himself after he learned the outcome of Col. Masters' trial. The combined efforts of Chappy and Doug's team result in a meticulously planned mission and the procurement of two heavily armed F-16B planes, with Doug flying the second unit.
On the day of Col. Masters' execution, Doug and Chappy fly their planes to the Mediterranean Sea and cross into the enemy state's airspace. In the ensuing battle, they take out three MiG-23 fighters and destroy an airfield, but Chappy's plane is damaged by an anti-aircraft gun. He tells Doug to climb to a high altitude and play the tape he made him the night before, then his engine fails and Doug listens as Chappy's fighter goes down. Chappy's recorded voice gives Doug encouragement and details that help him to complete the mission and rescue his father. Making the enemy believe he is leading a squadron, Doug threatens the enemy state into releasing his father for pickup. Before Doug lands his plane, Col. Masters is shot by a sniper, causing Doug to destroy the airbase and engulf the runway with napalm to keep the army at bay while he lands and picks up his wounded father. Just as they take off, Doug and his father encounter another group of MiGs led by Col. Akir Nakeshn, himself an ace pilot. The lone F-16 and Nakesh's MiG engage in a dogfight until a missile from Doug finishes off Nakesh. Low on fuel and ammunition, the F-16 is pursued by the other enemy MiGs when a squadron of U.S. Air Force F-16s appear, warding off the MiGs before escorting Doug and his father to Ramstein Air Base in West Germany.
While Col. Masters is being treated for his wounds, Doug is reunited with Chappy, who had ejected from his plane and was picked up by an Egyptian fishing trawler. The two are summoned by an Air Force judiciary panel for their reckless actions. Seeing that any form of punishment for the duo would expose an embarrassing lapse in Air Force security, the panel forgoes prosecution as long as Doug and Chappy never speak of their operation to anyone. In addition, Chappy convinces the panel to grant Doug admission to the Air Force Academy. Days later, a plane assigned by the President returns to the U.S., reuniting Doug, Chappy, and Col. Masters with family and friends.

Question: What damages Chappy's plane?
Answer: An anti-aircraft gun