BROADCAST WEATHER

The most common method used by flight crews to obtain specific inflight weather information is to use a source that broadcasts weather for the specific airport. Information about ceilings, visibility, wind, temperature, barometric pressure, and field conditions can be obtained from most types of broadcast weather services. Broadcast weather can be transmitted to the aircraft in radio voice format or digital format, if it is available, via an ACARS system.

AUTOMATIC TERMINAL INFORMATION SERVICE

The weather broadcast system found most often at airports with air traffic control towers in the National Airspace System (NAS) is the automatic terminal information service (ATIS). The AIM defines ATIS as the continuous broadcast of recorded non-control information in selected high activity terminal areas. The main purpose of ATIS is the reduction of frequency congestion and controller workload. It is broadcast over very high frequency (VHF) radio frequencies, and is designed to be receivable up to 60 NM from the transmitter at altitudes up to 25,000 feet above ground level(AGL). ATIS is typically derived from an automated weather observation system or a human weather observer’s report.

AUTOMATED WEATHER OBSERVING PROGRAMS

Automated surface observation systems can provide pilots with weather information over discrete VHF frequencies or over the voice portion of local NAVAIDs.The automated weather observing system (AWOS) and automated surface observing system (ASOS) provide real-time weather information that can be used by flight crews to make approach decisions, and by the NWS to generate aviation routine weather reports (METARs). Flight crews planning approaches to airports where ATIS is not available may be able to obtain current airport conditions from an AWOS/ASOS facility.

FAA-owned and operated AWOS-2 and AWOS-3 systems are approved sources of weather for Part 121 and 135 operations. Also, NWS-operated ASOSs are approved sources of weather for Part 121 and 135 operations. An AWOS/ASOS cannot be used as an authorized weather source for Part 121 or 135 instrument flight rules (IFR) operations if the visibility or altimeter setting is reported missing from the report. Refer to the AIM for the most current information on automated weather observation systems.

CENTER WEATHER

In the event that an airport has weather observation capability, but lacks the appropriate equipment to transmit that information over a radio frequency, air route traffic control centers (ARTCCs) can provide flight crews with hourly METAR or non-routine (special) aviation weather report (SPECI) information for those airports. For example, as an aircraft approaches an airport, the center controller can voluntarily or upon request provide the pilot with the most recent weather observation. Terminal Radar Approach Control (TRACON) facilities also provide weather observation information on a workload- permitting basis. Another option to obtain a current METAR or SPECI is to contact an En Route Flight Advisory Service facility (Flight Watch).

REGULATORY REQUIREMENTS

There are many practical reasons for reviewing weather information prior to initiating an instrument approach. Pilots must familiarize themselves with the condition of individual airports and runways so that they may make informed decisions regarding fuel management, diversions, and alternate planning. Because this information is critical, CFRs require pilots to comply with specific weather minimums for planning and execution of instrument flights and approaches.

PART 91 OPERATORS

According to Part 91.103, the pilot in command must become familiar with all available information concerning a flight prior to departure. Included in this directive is the fundamental basis for pilots to review NOTAMs and pertinent weather reports and forecasts for the intended route of flight. This review should include current weather reports and terminal forecasts for all intended points of landing and alternate airports. In addition, a thorough review of an airport’s current weather conditions should always be conducted prior to initiating an instrument approach. Pilots should also consider weather information as a planning tool for fuel management.

For flight planning purposes, weather information must be reviewed in order to determine the necessity and suitability of alternate airports. For Part 91 operations, the 600-2 and 800-2 rule applies to airports with precision and nonprecision approaches, respectively. Approaches with vertical guidance (APV) are considered semi-precision and nonprecision since they do not meet the International Civil Aviation Organization (ICAO) Annex 10 standards for a precision approach. (See Final Approach Segment section later in this chapter for more information regarding APV approaches.) Exceptions to the 600-2 and 800-2 alternate minimums are listed in the front of the National Aeronautical Charting Office (NACO) U.S. Terminal Procedures Publication (TPP) and are indicated by an “ ” symbol on the approach charts for the airport. This does not preclude flight crews from initiating instrument approaches at alternate airports when the weather conditions are below these minimums. The 600-2 and 800-2 rules, or any exceptions, only apply to flight planning purposes, while published landing minimums apply to the actual approach at the alternate.