Aeronautical Information Manual (AIM), page 483

Index   482 -- Page 483 -- 484


7-1-18. Estimating Intensity of Snow or
Drizzle (Based on Visibility)

a. Light. Visibility more than 1/2 statute mile.

b. Moderate. Visibility from more than 1/4 stat-

ute mile to 1/2 statute mile.

c. Heavy. Visibility 1/4 statute mile or less.

7-1-19. Pilot Weather Reports (PIREPs)

a. FAA air traffic facilities are required to solicit

PIREPs when the following conditions are reported

or forecast: ceilings at or below 5,000 feet; visibility

at or below 5 miles (surface or aloft); thunderstorms
and related phenomena; icing of light degree or
greater; turbulence of moderate degree or greater;
wind shear and reported or forecast volcanic ash

b. Pilots are urged to cooperate and promptly

volunteer reports of these conditions and other

atmospheric data such as: cloud bases, tops and

layers; flight visibility; precipitation; visibility

restrictions such as haze, smoke and dust; wind at

altitude; and temperature aloft.

c. PIREPs should be given to the ground facility
with which communications are established; i.e.,
FSS, ARTCC, or terminal ATC. One of the primary
duties of the Inflight position is to serve as a
collection point for the exchange of PIREPs with en
route aircraft.

d. If pilots are not able to make PIREPs by radio,
reporting upon landing of the inflight conditions

encountered to the nearest FSS or Weather Forecast

Office will be helpful. Some of the uses made of the
reports are:

1. The ATCT uses the reports to expedite the
flow of air traffic in the vicinity of the field and for
hazardous weather avoidance procedures.

2. The FSS uses the reports to brief other pilots,
to provide inflight advisories, and weather avoidance
information to en route aircraft.

3. The ARTCC uses the reports to expedite the
flow of en route traffic, to determine most favorable
altitudes, and to issue hazardous weather information
within the center's area.

4. The NWS uses the reports to verify or amend
conditions contained in aviation forecast and
advisories. In some cases, pilot reports of hazardous
conditions are the triggering mechanism for the
issuance of advisories. They also use the reports for

pilot weather briefings.

5. The NWS, other government organizations,

the military, and private industry groups use PIREPs
for research activities in the study of meteorological
6. All air traffic facilities and the NWS forward

the reports received from pilots into the weather

distribution system to assure the information is made

available to all pilots and other interested parties.

e. The FAA, NWS, and other organizations that
enter PIREPs into the weather reporting system use
the format listed in TBL 7-1-7. Items 1 through 6 are
included in all transmitted PIREPs along with one or
more of items 7 through 13. Although the PIREP

should be as complete and concise as possible, pilots

should not be overly concerned with strict format or

phraseology. The important thing is that the

information is relayed so other pilots may benefit

from your observation. If a portion of the report needs

clarification, the ground station will request the
information. Completed PIREPs will be transmitted
to weather circuits as in the following examples:
1. KCMH UA /OV APE 230010/TM 1516/FL085/TP

1. One zero miles southwest of Appleton VOR; time
1516 UTC; altitude eight thousand five hundred; aircraft
type BE200; bases of the broken cloud layer is six thousand

five hundred; flight visibility 3 miles with haze and smoke;
air temperature 20 degrees Celsius; light turbulence.

1815/FL120//TP BE99/SK IMC/WX RA/TA M08 /WV
2. From 15 miles north of Beckley VOR to Charles-
ton VOR; time 1815 UTC; altitude 12,000 feet; type
aircraft, BE-99; in clouds; rain; temperature minus
8 Celsius; wind 290 degrees magnetic at 30 knots; light to
moderate turbulence; light rime icing during climb
northwestbound from Roanoke, VA, between 8,000 and
10,000 feet at 1750 UTC.

Meteorology 7-1-39

Page 483 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   482 -- Page 483 -- 484