An operational reliability system includes a flight grouping module, a block modification module, and a pairing optimizer. The system evaluates potential modifications to scheduled flight block time and quantifies associated changes in on-time performance B0. The system also evaluates the impact of block modifications to headcount, regulatory compliance, operating expenses, and so forth. Via use of the operational reliability system, compliance with external regulations, for example Federal Aviation Regulations (FAR), may be achieved with a higher degree of probability.