Chapter 2: Airspace Classification, Operating Requirements, and Flight Restrictions o Hydrography  o Relief  Notices to Airmen, or NOTAMs, are time-critical aeronautical information either temporary in nature  or not sufficiently known in advance to permit publication on aeronautical charts or in other  operational publications. The information receives immediate dissemination via the National Notice to  Airmen (NOTAM) System. NOTAMs contain current notices to airmen that are considered essential to  the safety of flight, as well as supplemental data affecting other operational publications. There are  many different reasons that NOTAMs are issued. Following are some of those reasons: NOTAMs are available in printed form through subscription from the Superintendent of Documents  or online at  PilotWeb, which provides access to current NOTAM information. Local airport NOTAMs  can be obtained online from various websites. Some examples are www.fltplan.com and  www.aopa.org/whatsnew/notams.html. Most sites require a free registration and acceptance of  terms but offer pilots updated NOTAMs and TFRs. Remote Pilot – Small Unmanned Aircraft Systems Study Guide  13  • Hazards, such as air shows, parachute jumps, kite flying, and rocket launches • Flights by important people such as heads of state • Inoperable lights on tall obstructions • Temporary erection of obstacles near airfields • Passage of flocks of birds through airspace (a NOTAM in this category is known as a BIRDTAM) Notices to Airmen (NOTAMs)