What is crucial to check for proper function during pre-flight procedures?

Checking guarded switchlights during pre-flight procedures is essential because these switchlights indicate the operational status of various aircraft systems. Ensuring that guarded switchlights function properly is vital for flight safety, as they provide critical information that confirms whether specific systems are active, armed, or in standby mode. If any switchlights are malfunctioning, it could mean that important systems may not operate as required in-flight, potentially leading to safety risks.

While engine oil temperature, cabin lighting, and weather radar are all important for overall aircraft operation and safety, the guarding feature of these switches particularly highlights the importance of making sure that crucial systems are managed and controlled correctly right from the start of the flight. Thus, verifying the functionality of guarded switchlights ensures that pilots receive the correct indications needed to make informed operational decisions during the flight.