Final answer:
The flight data recorder (FDR) EVENT switch allows pilots to manually mark significant moments during a flight for future review, assisting in investigations or maintenance checks by creating a timestamp in the FDR data.
Step-by-step explanation:
Pressing the flight data recorder (FDR) EVENT switch is a function used by pilots during a flight to manually mark a specific part of the flight data for later review. It is generally used to flag data if something unusual or significant occurs during the flight that the crew believes should be investigated later. It's particularly useful for instances that may not trigger an automatic event on the FDR. When pressed, it creates a timestamp in the FDR data stream that investigators or maintenance personnel can easily find after the flight has ended.