SOP Standard Operating Procedures in Flight Operations are defined as strict procedures covering every aspect of flight deck activity and embracing normal, abnormal and emergency situations.
This wide range of SOP Standard Operating Procedures  and checklists is essential because of the large number of situations which can arise and the critical nature of some of these situations.

Although these SOP Standard Operating Procedures are written down in checklists and quick reference handbooks, pilots must be able to perform certain vital actions from memory, referring to the written procedure later to confirm that correct action has been taken.

Flight Operations procedures have been defined after much research in order to ensure the most successful outcome from all reasonably likely circumstances. They are not discretionary and must be followed precisely. Failure to follow established procedures has been found to be a causal factor in many aircraft accidents and serious incidents.