Aeronautical Information Manual (AIM), page 488

Index   487 -- Page 488 -- 489


7-1-23. Wind Shear PIREPs

a. Because unexpected changes in wind speed and

direction can be hazardous to aircraft operations at

low altitudes on approach to and departing from

airports, pilots are urged to promptly volunteer

reports to controllers of wind shear conditions they

encounter. An advance warning of this information

will assist other pilots in avoiding or coping with a

wind shear on approach or departure.

b. When describing conditions, use of the terms
"negative" or "positive" wind shear should be

avoided. PIREPs of "negative wind shear on final,"
intended to describe loss of airspeed and lift, have
been interpreted to mean that no wind shear was
encountered. The recommended method for wind

shear reporting is to state the loss or gain of airspeed
and the altitudes at which it was encountered.


1. Denver Tower, Cessna 1234 encountered wind shear,
loss of 20 knots at 400.

2. Tulsa Tower, American 721 encountered wind shear on
final, gained 25 knots between 600 and 400 feet followed
by loss of 40 knots between 400 feet and surface.

1. Pilots who are not able to report wind shear in
these specific terms are encouraged to make reports
in terms of the effect upon their aircraft.
Miami Tower, Gulfstream 403 Charlie encountered an
abrupt wind shear at 800 feet on final, max thrust required.
2. Pilots using Inertial Navigation Systems
(INSs) should report the wind and altitude both above
and below the shear level.

7-1-24. Clear Air Turbulence (CAT) PIREPs

CAT has become a very serious operational factor to
flight operations at all levels and especially to jet


traffic flying in excess of 15,000 feet. The best
available information on this phenomenon must

come from pilots via the PIREP reporting procedures.

All pilots encountering CAT conditions are urgently

requested to report time, location, and intensity (light,

moderate, severe, or extreme) of the element to the

FAA facility with which they are maintaining radio

contact. If time and conditions permit, elements

should be reported according to the standards for

other PIREPs and position reports.

AIM, Paragraph 7-1-22 , PIREPs Relating to Turbulence

7-1-25. Microbursts

a. Relatively recent meteorological studies have

confirmed the existence of microburst phenomenon.

Microbursts are small scale intense downdrafts
which, on reaching the surface, spread outward in all
directions from the downdraft center. This causes the
presence of both vertical and horizontal wind shears

that can be extremely hazardous to all types and
categories of aircraft, especially at low altitudes. Due
to their small size, short life span, and the fact that
they can occur over areas without surface precipita-
tion, microbursts are not easily detectable using
conventional weather radar or wind shear alert

b. Parent clouds producing microburst activity
can be any of the low or middle layer convective
cloud types. Note, however, that microbursts
commonly occur within the heavy rain portion of

thunderstorms, and in much weaker, benign
appearing convective cells that have little or no
precipitation reaching the ground.

7-1-44 Meteorology

Page 488 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   487 -- Page 488 -- 489