Which of the following advisories would be issued for conditions affecting all aircraft?

The advisory that is issued for conditions affecting all aircraft is the SIGMET. SIGMETs are significant meteorological information alerts that inform pilots of severe weather conditions that may affect the safety of flight for all types of aircraft. This includes phenomena such as severe turbulence, icing, thunderstorms, volcanic ash, and dust storms, among others.

Unlike AIRMETs, which are tailored for conditions that primarily affect smaller or less capable aircraft, SIGMETs address severe conditions that could impact larger commercial airliners as well, making them universally relevant for all flying operations.

Additionally, while CONVECTIVE SIGMETs are also significant, they are specifically related to convective weather phenomena and primarily concerned with thunderstorms. METARs, on the other hand, provide routine aviation weather observations but do not serve as advisories like SIGMETs do. Therefore, SIGMETs are crucial for ensuring that all pilots are aware of hazardous meteorological conditions that could jeopardize flight safety.