OREANDA-NEWS. Southwest Airlines discovered an overdue maintenance check required to be performed on the standby hydraulic system, which serves as a back-up to the primary hydraulic systems. As a result of this discovery, 128  -700 aircraft were identified as having overflown a required check. Once identified, Southwest immediately and voluntarily removed the affected aircraft from service, initiated maintenance checks, disclosed the matter to the FAA, and developed an action plan to complete all overdue checks. The FAA approved a proposal that would allow Southwest to continue operating the aircraft for a maximum of five days as the checks are completed. Approximately 80 cancellations occurred today as a result of the events and the airline is anticipating a very minimal impact to their operations tomorrow. The Safety of our Customers and Employees remains our highest priority and we are working quickly to resolve the situation.