An operator proficiency check (OPC) is a mandatory assessment program conducted by airlines to evaluate the performance and competence of pilots in executing normal, abnormal, and emergency procedures. OPCs typically occur every six months and involve an examiner assessing pilots' abilities using the airline's flight crew training resources and following defined standards and recommended practices.

OPCs typically occur every 6 months, and the validity begins from the initial expiry date. Since the last OPC was valid until the 30th of June, and the next OPC is executed (15th of April), if we count from the initial expiry date (30th of June) and add 6 months, the result is 31st of December the same year.