Which report indicates braking action that is less than good?

The correct answer is PIREP, which stands for Pilot Report. PIREPs are essential communication tools used by pilots to report actual meteorological conditions encountered in the air, including information on turbulence, icing, and runway conditions. Specifically, when it comes to braking action, PIREPs provide firsthand accounts from pilots regarding the conditions they experience while landing.

When braking action is reported as "less than good," it typically reflects adverse conditions that could affect the aircraft's ability to stop safely, such as wet or icy runways. This makes PIREPs a crucial source of real-time information for other pilots and air traffic controllers, allowing them to make informed decisions about landings and takeoffs.

The other options do not communicate braking action conditions directly. Surface wind reports focus on wind conditions, volcanic ash reports deal with the presence of ash affecting air quality and safety, and flight advisories generally provide broader information about air traffic, weather patterns, or hazards, but they do not specifically report on braking actions encountered by pilots.