What was found
GOT YELLOW ALT FLAG AT FL280. AT FL280 CA ALTIMETER SHOWED 28260, FO ALTIMETER SHOWED 28000, STANDBY SHOWED 28080. SUSPECTED INTEGRATED PITOT/STATIC/AOA SENSOR 1 AT FAULT. RAR INTEGRATED PITOT/STATIC/AOA SENSOR IAW AMM 34-13-01, OPC GOOD