To identify the vulnerability of recovery sleep, this study investigated the occurrence of obstructive sleep apnea during daytime sleep following overnight flights in healthy airline pilots. We conducted daytime polysomnography following a long-haul night-time flight in 103 pilots. The following variables were assessed: apnea–hypopnea index, respiratory disturbance index and oxygen desaturation index. Moderate-to-severe obstructive sleep apnea was defined as an apnea–hypopnea index ≥15. Seventy-three pilots (70.9%) with no known history of obstructive sleep apnea presented with moderate-to-severe obstructive sleep apnea. Pilots showed high mean apnea–hypopnea, respiratory disturbance and oxygen desaturation indices. The body mass index, Berlin questionnaire score and cumulative flight time contributed to these indices, with both body mass index and cumulative flight time remaining significant at an apnea–hypopnea index ≥15. We found that pilots are vulnerable to obstructive sleep apnea during daytime sleep after night-time flights, which may deteriorate their health, increase fatigue and impair overall flight safety. Further research is needed to ensure flight safety, as daytime recovery sleep is unavoidable for night-time flight pilots. The pilots' normal and recovery sleep patterns should both be studied to develop an effective sleep management protocol.