InFO 07008: Precipitation Reports From ATC—New Terms

InFOInformation for Operators

U.S. Department InFO 07008

of Transportation DATE: 4/4/07

Federal Aviation

Administration Flight Standards Service

Washington, DC http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/info An InFO contains valuable information for operators that should help them meet certain administrative, regulatory, or operational requirements with relatively low urgency or impact on safety.

Subject: Precipitation Reports From ATC—New Terms

Purpose: This InFO announces a four-level scheme of precipitation observations now used by air traffic controllers (ATC), and corresponding terms used in reporting precipitation to pilots.

Discussion: ATC work stations normally use a weather processing system, permitting a controller to see, and report to pilots, four levels of precipitation as a function of reflectivity expressed in decibels (dBZ), as follows:

“LIGHT” < 30 dBZ* Rainfall rate of .01 – .10 inches per hour “MODERATE” 30 to 40 dBZ Rainfall rate of .175 – .50 inches per hour “HEAVY” > 40 to 50 dBZ Rainfall rate of .5 – 2.0 inches per hour “EXTREME” > 50 dBZ Rainfall rate of 2.0 – 16+ inches per hour *Air Route Traffic Control Center (ARTCC, also known as “center radar”) controllers will not use the term “LIGHT” because their systems do not display “LIGHT” precipitation. (This information will be included in August 2007 update to the Aeronautical Information Manual.)

None of the air traffic control weather processing systems distinguish between types of precipitation such as snow, rain, hail, or ice pellets (sleet). Hence all observations reported to pilots are expressed as “precipitation.” Pilots should understand that precipitation data may be up to 6 minutes old when actually displayed to a controller.

For more information, see Chapter 7, page 7-1-38 in the current edition of the Aeronautical Information Manual (AIM), revised 3/15/07. The AIM can be found at the following URL: http://www.faa.gov/airports_airtraffic/air_traffic/publications/atpubs/aim/. Any questions regarding the content of this InFO should be directed to Mike Lenz, Program Analyst for the Certification and General Aviation Operations Branch, AFS-810 at (202) 267-7949.

Recommended Action: Directors of safety, directors of operations, fractional ownership program managers, trainers, and pilots should be aware of the implementation and meanings of new terms used by ATC when reporting precipitation to pilots, and ensure that those terms are addressed in training programs used by pilots.

Approved by: AFS-200