This information used to be covered in AFI48-123, but now lies in DODI6130.03 and is references in AFI48-123:
ENCLOSURE 4: MEDICAL STANDARDS FOR APPOINTMENT, ENLISTMENT, OR INDUCTION
11. LUNGS, CHEST WALL, PLEURA, AND MEDIASTINUM
h. Current chest wall malformation (754.89), including but not limited to pectus excavatum (754.81) or pectus carinatum (754.82), if these conditions interfere with vigorous physical exertion.
There are current and former fighter pilots in the USAF and USN/USMC with asymptomatic pectus excavatum.
