Checkliststs are tools that assist on flight crew’s airmanship memory and ensure that all required actions are performed correctly and in an orderly manner. Checklists (normal and non-normal) are usually bundled in an easy-to-use Quick Reference Handbook (QRH).
Challenge-and-response checklists usually relate to the normal operation of the aircraft (normal procedures) for each phase of flight. Flight-phase related actions are performed from memory following a cockpit flow pattern.
Specific critical items are checked /cross-checked using a challenge-and-response checklist, whereby thepilot monitoring reads the items to be checked and the pilot flying confirms the proper configuration of the appropriate items (e.g., altimeter setting, flaps position, ground spoilers arming, etc.).
On aircraft equipped with electronic checklists, when crew actions are completed the checklist items may be automatically sensed by the system and erased or the colour of the checked item may change. On some aircraft models, activating a prompt allows annotating the item as being "checked".
Read-and-do lists usually relate to non-normal (abnormal and emergency) procedures for which a cockpit flow pattern performed from memory is not suitable. Indeed, non-normal procedures usually include pre-conditions that must be assessed and mutually agreed by both crew members before proceeding.
Some non-normal procedures (such as the recovery from an unusual attitude or flight with an unreliable airspeed indication) include "memory items" that could also be called "survival items". These are items that are time critical and must be accomplished from memory before referring to the QRH for the further management of the prevailing contingency.
Checklists, both normal and non-normal, are important assets that assist the flight crew in the safe and proper operation of the aircraft. They should not be altered without referring to the manufacturer's flight operations department. More critically, altering a non-normal procedure might, at best, affect secondary failures (failure conditions resulting from a primary malfunction) and possibly prevent the recovery of an affected system. At worst an altered checklist may further degrade the situation and possibly increase instead of decrease the risk.