PIREPs (Pilot Weather Reports) are short coded messages that help assist other pilots with flight planning and preparation by reporting observed weather conditions. There are two main types of PIREPs, UA and UUA.
UA designates a routine report, while UUA designates an urgent report.
Items classified as urgent or UUA would be:
“Making a PIREP is the most direct way that you can help another pilot.”NASA
AIREPs (Air-Reports) are really the same thing as a PIREP, however, they are generated automatically by onboard computer equipment and sent back to the ground to be used by pilots and dispatchers to better plan routes for other flights. These are common for aircraft flying over the oceans where weather forecasting and weather observation stations are far fewer than over land. While most AIREPs are automatic from the aircraft to ground stations, the pilot generally has means through onboard computers to manually send an AIREP back to the ground. AIREPs contain all the same information as PIREPs and generally a bit more, but that information is obtained from onboard sensors rather than an observation by the pilot.
As you depart on a cross country flight and reach cruising altitude you note a scattered to broken layer forming at 4,500′ agl. While this should not impact your short cross country flight, this is different from the 10sm and Clear Sky forecast that was originally along your route of flight, so you make a PIREP with the nearest flight service station to let them and other pilots know of the changing conditions in that area so that others may be more prepared before taking off in their aircraft.