30 AUG 07
AIP
United States of America
GEN 3.5-41
15 MAR 07
Federal Aviation Administration Nineteenth Edition
22. PIREPs Relating to Turbulence
22.1 When encountering turbulence, pilots are
urgently requested to report such conditions to ATC
as soon as practicable. PIREPs relating to turbulence
should state:
22.1.1 Aircraft location.
22.1.2 Time of occurrence in UTC.
22.1.3 Turbulence intensity.
22.1.4 Whether the turbulence occurred in or near
clouds.
22.1.5 Aircraft altitude, or flight level.
22.1.6 Type of aircraft.
22.1.7 Duration of turbulence.
EXAMPLE-
1. Over Omaha, 1232Z, moderate turbulence in clouds at
Flight Level three one zero, Boeing 707.
2. From five zero miles south of Albuquerque to three zero
miles north of Phoenix, 1250Z, occasional moderate chop
at Flight Level three three zero, DC8.
22.2 Duration and classification of intensity should
be made using TBL GEN 3.5-10, Turbulence
Reporting Criteria Table.
TBL GEN 3.5-10
Turbulence Reporting Criteria Table
Intensity Aircraft Reaction Reaction inside Aircraft Reporting Term-Definition
Light Turbulence that momentarily causes
slight, erratic changes in altitude
and/or attitude (pitch, roll, yaw).
Report as Light Turbulence; 1
or
Turbulence that causes slight, rapid
and somewhat rhythmic bumpiness
without appreciable changes in altitude
or attitude. Report as Light Chop.
Occupants may feel a slight strain
against seat belts or shoulder straps.
Unsecured objects may be displaced
slightly. Food service may be
conducted, and little or no difficulty is
encountered in walking.
Occasional-Less than 1
/3 of the time.
Intermittent-1
/3 to 2
/3.
Continuous-More than 2
/3.
Moderate Turbulence that is similar to Light
Turbulence but of greater intensity.
Changes in altitude and/or attitude
occur, but the aircraft remains in
positive control at all times. It usually
causes variations in indicated airspeed.
Report as Moderate Turbulence; 1
or
Turbulence that is similar to Light
Chop but of greater intensity. It causes
rapid bumps or jolts without
appreciable changes in aircraft altitude
or attitude. Report as Moderate Chop.
1
Occupants feel definite strains against
seat belts or shoulder straps.
Unsecured objects are dislodged. Food
service and walking are difficult.
NOTE
1. Pilots should report location(s), time
(UTC), intensity, whether in or near
clouds, altitude, type of aircraft and,
when applicable, duration of
turbulence.
2. Duration may be based on time
between two locations or over a single
location. All locations should be
readily identifiable.
Severe Turbulence that causes large, abrupt
changes in altitude and/or attitude. It
usually causes large variations in
indicated airspeed. Aircraft may be
momentarily out of control. Report as
Severe Turbulence.1
Occupants are forced violently against
seat belts or shoulder straps.
Unsecured objects are tossed about.
Food service and walking are
impossible.
EXAMPLES:
a. Over Omaha. 1232Z, Moderate
Turbulence, in cloud, Flight Level 310,
B707.
Extreme Turbulence in which the aircraft is
violently tossed about and is
practically impossible to control. It
may cause structural damage. Report
as Extreme Turbulence. 1
b. From 50 miles south of Albuquerque
to 30 miles north of Phoenix, 1210Z to
1250Z, occasional Moderate Chop,
Flight Level 330, DC8.
1
High level turbulence (normally above 15,000 feet ASL) not associated with cumuliform cloudiness, including thunderstorms,
should be reported as clear air turbulence (CAT) preceded by the appropriate intensity, or light or moderate chop.
30 AUG 07
AIP
United States of America
GEN 3.5-42
15 MAR 07
Federal Aviation Administration Nineteenth Edition
23. Wind Shear PIREPs
23.1 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.
23.2 When describing conditions, the 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/gain of airspeed and
the altitude(s) at which it was encountered.
EXAMPLE-
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.
Pilots using Inertial Navigation Systems should
report the wind and altitude both above and below the
shear layer.
EXAMPLE-
Miami Tower, Gulfstream 403 Charlie encountered an
abrupt wind shear at 800 feet on final, max thrust required.
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.
24. Clear Air Turbulence (CAT) PIREPs
24.1 Clear air turbulence (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
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. See
TBL GEN 3.5-10, Turbulence Reporting Criteria
Table.
25. Microbursts
25.1 Relatively recent meteorological studies have
confirmed the existence of microburst phenomena.
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
systems.
25.2 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-appear-
ing convective cells that have little or no precipitation
reaching the ground.
25.3 The life cycle of a microburst as it descends in
a convective rain shaft is seen in FIG GEN 3.5-8,
Evolution of a Microburst. An important consideration
for pilots is the fact that the microburst intensifies for
about 5 minutes after it strikes the ground.
25.4 Characteristics of microbursts include:
25.4.1 Size. The microburst downdraft is typically
less than 1 mile in diameter as it descends from the
cloud base to about 1,000-3,000 feet above the
ground. In the transition zone near the ground, the
downdraft changes to a horizontal outflow that can
extend to approximately 2 1
/2 miles in diameter.
25.4.2 Intensity. The downdrafts can be as strong
as 6,000 feet per minute. Horizontal winds near the
surface can be as strong as 45 knots resulting in a
90-knot shear (headwind to tailwind change for a
traversing aircraft) across the microburst. These
strong horizontal winds occur within a few hundred
feet of the ground.
25.4.3 Visual Signs. Microbursts can be found
almost anywhere that there is convective activity.
They may be embedded in heavy rain associated with
a thunderstorm or in light rain in benign- appearing
virga. When there is little or no precipitation at the
surface accompanying the microburst, a ring of
blowing dust may be the only visual clue of its
existence.
30 AUG 07
AIP
United States of America
GEN 3.5-43
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-8
Evolution of a Microburst
5 -in -2 in 5 in 10 in
HEIGHT (feet)
10,000
5,000
WIND SPEED
20 10-nots
20 nots
SCALE (miles)
0 1 2 3
Vertical cross section of the evolution of a microburst wind field. T is the time of initial divergence at
the surface. The shading refers to the vector wind speeds. Figure adapted from Wilson et al., 1984,
Microburst Wind Structure and Evaluation of Doppler Radar for Wind Shear Detection, DOT/FAA
Report No. DOT/FAA/PM-84/29, National Technical Information Service, Springfield, VA 37 pp.
25.4.4 Duration. An individual microburst will
seldom last longer than 15 minutes from the time it
strikes the ground until dissipation. The horizontal
winds continue to increase during the first 5 minutes
with the maximum intensity winds lasting approxi-
mately 2-4 minutes. Sometimes microbursts are
concentrated into a line structure and, under these
conditions, activity may continue for as long as
1_hour. Once microburst activity starts, multiple
microbursts in the same general area are not
uncommon and should be expected.
30 AUG 07
AIP
United States of America
GEN 3.5-44
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-9
Microburst Encounter During Takeoff
NOTE-
A microburst encounter during takeoff. The airplane first encounters a headwind and experiences increasing performance
(1), this is followed in short succession by a decreasing headwind component (2), a downdraft (3), and finally a strong
tailwind (4), where 2 through 5 all result in decreasing performance of the airplane. Position (5) represents an extreme
situation just prior to impact. Figure courtesy of Walter Frost, FWG Associates, Inc., Tullahoma, Tennessee.
25.5 Microburst wind shear may create a severe
hazard for aircraft within 1,000 feet of the ground,
particularly during the approach to landing and
landing and take-off phases. The impact of a
microburst on aircraft which have the unfortunate
experience of penetrating one is characterized in
FIG GEN 3.5-9. The aircraft may encounter a
headwind (performance increasing), followed by a
downdraft and a tailwind (both performance
decreasing), possibly resulting in terrain impact.
30 AUG 07
AIP
United States of America
GEN 3.5-45
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-10
25.6 Detection of Microbursts, Wind Shear, and
Gust Fronts
25.6.1 FAA's Integrated Wind Shear Detection
Plan
25.6.1.1 The FAA currently employs an integrated
plan for wind shear detection that will significantly
improve both the safety and capacity of the majority
of the airports currently served by the air carriers.
This plan integrates several programs, such as the
Integrated Terminal Weather System (ITWS),
Terminal Doppler Weather Radar (TDWR), Weather
System Processor (WSP), and Low Level Wind Shear
Alert Systems (LLWAS) into a single strategic
concept that significantly improves the aviation
weather information in the terminal area.
(See FIG GEN 3.5-10.)
25.6.1.2 The wind shear/microburst information and
warnings are displayed on the ribbon display
terminal (RBDT) located in the tower cabs. They are
identical (and standardized) to those in the LLWAS,
TDWR and WSP systems, and designed so that the
controller does not need to interpret the data, but
simply read the displayed information to the pilot.
The RBDTs are constantly monitored by the
controller to ensure the rapid and timely dissemina-
tion of any hazardous event(s) to the pilot.
30 AUG 07
AIP
United States of America
GEN 3.5-46
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-11
25.6.1.3 The early detection of a wind shear/micro-
burst event, and the subsequent warning(s) issued to
an aircraft on approach or departure, will alert the
pilot/crew to the potential of, and to be prepared for,
a situation that could become very dangerous!
Without these warnings, the aircraft may NOT be able
to climb out of or safely transition the event, resulting
in a catastrophe. The air carriers, working with the
FAA, have developed specialized training programs
using their simulators to train and prepare their pilots
on the demanding aircraft procedures required to
escape these very dangerous wind shear and/or
microburst encounters.
25.6.1.4 Low Level Wind Shear Alert System
(LLWAS)
a) The LLWAS provides wind data and software
processes to detect the presence of hazardous wind
shear and microbursts in the vicinity of an airport.
Wind sensors, mounted on poles sometimes as high
as 150 feet, are (ideally) located 2,000 - 3,500 feet,
but not more than 5,000 feet, from the centerline of
the runway. (See FIG GEN 3.5-11.)
b) The LLWAS was fielded in 1988 at 110 airports
across the nation. Many of these systems have been
replaced by new terminal doppler weather radar
(TDWR) and weather systems processor (WSP)
technology. Eventually all LLWAS systems will be
phased out; however, 39 airports will be upgraded to
the LLWAS-NE (Network Expansion) system,
which employs the very latest software and sensor
technology. The new LLWAS-NE systems will not
only provide the controller with wind shear warnings
and alerts, including wind shear/microburst detection
at the airport wind sensor location, but will also
provide the location of the hazards relative to the
airport runway(s). It will also have the flexibility and
capability to grow with the airport as new runways are
built. As many as 32 sensors, strategically located
around the airport and in relationship to its runway
configuration, can be accommodated by the
LLWAS-NE network.
30 AUG 07
AIP
United States of America
GEN 3.5-47
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-12
25.6.1.5 Terminal Doppler Weather Radar
(TDWR)
a) TDWRs are being deployed at 45 locations
across the U.S. Optimum locations for TDWRs are
8_to 12 miles from the airport proper, and designed to
look at the airspace around and over the airport to
detect microbursts, gust fronts, wind shifts, and
precipitation intensities. TDWR products advise the
controller of wind shear and microburst events
impacting all runways and the areas 1
/2 mile on either
side of the extended centerline of the runways and to
a distance of 3 miles on final approach and 2 miles on
departure. FIG GEN 3.5-12 is a theoretical view of
the runway and the warning boxes that the software
uses to determine the location(s) of wind shear or
microbursts. These warnings are displayed (as
depicted in the examples in subparagraph e) on the
ribbon display terminal located in the tower cabs.
b) It is very important to understand what TDWR
DOES NOT DO:
1) It_DOES NOT warn of wind shear outside of
the alert boxes (on the arrival and departure ends of
the runways).
2) It_DOES NOT detect wind shear that is
NOT a microburst or a gust front.
3) It_DOES NOT detect gusty or cross wind
conditions.
4) It _DOES NOT detect turbulence.
However, research and development is continuing on
these systems. Future improvements may include
such areas as storm motion (movement), improved
gust front detection, storm growth and decay,
microburst prediction, and turbulence detection.
c) TDWR also provides a geographical situation
display (GSD) for supervisors and traffic manage-
ment specialists for planning purposes. The GSD
displays (in color) 6 levels of weather (precipitation),
gust fronts and predicted storm movement(s). This
data is used by the tower supervisor(s), traffic
management specialists, and controllers to plan for
runway changes and arrival/departure route changes
in order to reduce aircraft delays and increase airport
capacity.
25.6.1.6 Weather Systems Processor (WSP)
a) The WSP provides the controller, supervisor,
traffic management specialist, and ultimately the
pilot, with the same products as the terminal doppler
weather radar at a fraction of the cost. This is
accomplished by utilizing new technologies to access
the weather channel capabilities of the existing
ASR-9 radar located on or near the airport, thus
eliminating the requirements for a separate radar
location, land acquisition, support facilities, and the
associated communication landlines and expenses.
30 AUG 07
AIP
United States of America
GEN 3.5-48
15 MAR 07
Federal Aviation Administration Nineteenth Edition
b) The WSP utilizes the same RBDT display as the
TDWR and LLWAS, and, like the TDWR, has a GSD
for planning purposes by supervisors, traffic
management specialists, and controllers. The WSP
GSD emulates the TDWR display; i.e., it also depicts
6 levels of precipitation, gust fronts and predicted
storm movement, and like the TDWR, GSD is used
to plan for runway changes and arrival/departure
route changes in order to reduce aircraft delays and to
increase airport capacity.
c) This system is currently under development and
is operating in a developmental test status at the
Albuquerque, New Mexico, airport. When fielded,
the WSP is expected to be installed at 34 airports
across the nation, substantially increasing the safety
of flying.
25.6.1.7 Operational Aspects of LLWAS, TDWR,
and WSP
To demonstrate how this data is used by both the
controller and the pilot, 3 ribbon display examples
and their explanations are presented:
a) MICROBURST ALERTS
EXAMPLE-
This is what the controller sees on his/her ribbon display
in the tower cab.
27A MBA 35K- 2MF 250 20
NOTE-
(See FIG GEN 3.5-13 to see how the TDWR/WSP
determines the microburst location).
This is what the controller will say when issuing the
alert.
PHRASEOLOGY-
RUNWAY 27 ARRIVAL, MICROBURST ALERT, 35 KT
LOSS 2 MILE FINAL, THRESHOLD WINDS 250 AT 20.
In plain language, the controller is telling the pilot
that on approach to runway 27, there is a microburst
alert on the approach lane to the runway, and to
anticipate or expect a 35-knot loss of airspeed at
approximately 2 miles out on final approach (where
the aircraft will first encounter the phenomena). With
that information, the aircrew is forewarned, and
should be prepared to apply wind shear/microburst
escape procedures should they decide to continue the
approach. Additionally, the surface winds at the
airport for landing runway 27 are reported as
250_degrees at 20 knots.
NOTE-
Threshold wind is at pilot's request or as deemed
appropriate by the controller.
b) WIND SHEAR ALERTS
EXAMPLE-
This is what the controller sees on his/her ribbon display
in the tower cab.
27A WSA 20K- 3MF 200 15
NOTE-
(See FIG GEN 3.5-14 to see how the TDWR/WSP
determines the wind shear location).
This is what the controller will say when issuing the
alert.
PHRASEOLOGY-
RUNWAY 27 ARRIVAL, WIND SHEAR ALERT, 20 KT
LOSS 3 MILE FINAL, THRESHOLD WINDS 200 AT 15.
In plain language, the controller is advising the
aircraft arriving on runway 27 that at 3 miles out the
pilot should expect to encounter a wind shear
condition that will decrease airspeed by 20 knots and
possibly the aircraft will encounter turbulence.
Additionally, the airport surface winds for landing
runway 27 are reported as 200 degrees at 15 knots.
NOTE-
Threshold wind is at pilot's request or as deemed
appropriate by the controller.
30 AUG 07
AIP
United States of America
GEN 3.5-49
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-13
FIG GEN 3.5-14
30 AUG 07
AIP
United States of America
GEN 3.5-50
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-15
c) MULTIPLE WIND SHEAR ALERTS
EXAMPLE-
This is what the controller sees on his/her ribbon display
in the tower cab.
27A WSA 20K+ RWY 250 20
27D WSA 20K+ RWY 250 20
NOTE-
(See FIG GEN 3.5-15 to see how the TDWR/WSP
determines the gust front/wind shear location).
This is what the controller will say when issuing the
alert.
PHRASEOLOGY-
MULTIPLE WIND SHEAR ALERTS.
RUNWAY 27 ARRIVAL, WIND SHEAR ALERT, 20 KT
GAIN ON RUNWAY;
RUNWAY 27 DEPARTURE, WIND SHEAR ALERT, 20 KT
GAIN ON RUNWAY, WINDS 250 AT 20.
EXAMPLE-
In this example, the controller is advising arriving and
departing aircraft that they could encounter a wind shear
condition right on the runway due to a gust front
(significant change of wind direction) with the possibility
of a 20 knot gain in airspeed associated with the gust front.
Additionally, the airport surface winds (for the runway in
use) are reported as 250 degrees at 20 knots.
25.6.1.8 The Terminal Weather Information for
Pilots System (TWIP)
a) With the increase in the quantity and quality of
terminal weather information available through
TDWR, the next step is to provide this information
directly to pilots rather than relying on voice
communications from ATC. The National Airspace
System has long been in need of a means of delivering
terminal weather information to the cockpit more
efficiently in terms of both speed and accuracy to
enhance pilot awareness of weather hazards and to
reduce air traffic controller workload. With the TWIP
capability, terminal weather information, both
30 AUG 07
AIP
United States of America
GEN 3.5-51
15 MAR 07
Federal Aviation Administration Nineteenth Edition
alphanumerically and graphically, is now available
directly to the cockpit on a test basis at 9 locations.
b) TWIP products are generated using weather
data from the TDWR or the Integrated Terminal
Weather System (ITWS) testbed. TWIP products are
generated and stored in the form of text and character
graphic messages. Software has been developed to
allow TDWR or ITWS to format the data and send the
TWIP products to a database resident at Aeronautical
Radio, Inc. (ARINC). These products can then be
accessed by pilots using the ARINC Aircraft
Communications Addressing and Reporting System
(ACARS) data link services. Airline dispatchers can
also access this database and send messages to
specific aircraft whenever wind shear activity begins
or ends at an airport.
c) TWIP products include descriptions and
character graphics of microburst alerts, wind shear
alerts, significant precipitation, convective activity
within 30 NM surrounding the terminal area, and
expected weather that will impact airport operations.
During inclement weather; i.e., whenever a predeter-
mined level of precipitation or wind shear is detected
within 15 miles of the terminal area, TWIP products
are updated once each minute for text messages and
once every 5 minutes for character graphic messages.
During good weather (below the predetermined
precipitation or wind shear parameters) each message
is updated every 10 minutes. These products are
intended to improve the situational awareness of the
pilot/flight crew, and to aid in flight planning prior to
arriving or departing the terminal area. It is important
to understand that, in the context of TWIP, the
predetermined levels for inclement versus good
weather has nothing to do with the criteria for
VFR/MVFR/IFR/LIFR; it only deals with precipita-
tion, wind shears, and microbursts.
26. PIREPs Relating to Volcanic Ash Activity
26.1 Volcanic eruptions which send ash into the
upper atmosphere occur somewhere around the world
several times each year. Flying into a volcanic ash
cloud can be exceedingly dangerous. At least two
B747s have lost all power in all four engines after
such an encounter. Regardless of the type aircraft,
some damage is almost certain to ensue after an
encounter with a volcanic ash cloud.
26.2 While some volcanoes in the U.S. are
monitored, many in remote areas are not. These
unmonitored volcanoes may erupt without prior
warning to the aviation community. A pilot observing
a volcanic eruption who has not had previous
notification of it may be the only witness to the
eruption. Pilots are strongly encouraged to transmit a
PIREP regarding volcanic eruptions and any
observed volcanic ash clouds.
26.3 Pilots should submit PIREPs regarding volca-
nic activity using the Volcanic Activity Reporting
form (VAR) as illustrated in FIG GEN 3.5-30. (If a
VAR form is not immediately available, relay enough
information to identify the position and type of
volcanic activity.)
26.4 Pilots should verbally transmit the data required
in items 1 through 8 of the VAR as soon as possible.
The data required in items 9 through 16 of the VAR
should be relayed after landing, if possible.
27. Thunderstorms
27.1 Turbulence, hail, rain, snow, lightning, sus-
tained updrafts and downdrafts, and icing conditions
are all present in thunderstorms. While there is some
evidence that maximum turbulence exists at the
middle level of a thunderstorm, recent studies show
little variation of turbulence intensity with altitude.
27.2 There is no useful correlation between the
external visual appearance of thunderstorms and the
severity or amount of turbulence or hail within them.
Also, the visible thunderstorm cloud is only a portion
of a turbulent system whose updrafts and downdrafts
often extend far beyond the visible storm cloud.
Severe turbulence can be expected up to 20 miles
from severe thunderstorms. This distance decreases
to about 10 miles in less severe storms. These
turbulent areas may appear as a well-defined echo on
weather radar.
27.3 Weather radar, airborne or ground-based, will
normally reflect the areas of moderate to heavy
precipitation. (Radar does not detect turbulence.) The
frequency and severity of turbulence generally
increases with the areas of highest liquid water
content of the storm. NO FLIGHT PATH THROUGH
AN AREA OF STRONG OR VERY STRONG
RADAR ECHOES SEPARATED BY 20-30 MILES
OR LESS MAY BE CONSIDERED FREE OF
SEVERE TURBULENCE.
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GEN 3.5-52
15 MAR 07
Federal Aviation Administration Nineteenth Edition
27.4 Turbulence beneath a thunderstorm should not
be minimized. This is especially true when the
relative humidity is low in any layer between the
surface and 15,000 feet. Then the lower altitudes may
be characterized by strong out-flowing winds and
severe turbulence.
27.5 The probability of lightning strikes occurring to
aircraft is greatest when operating at altitudes where
temperatures are between -5 C and +5 C. Lightning
can strike aircraft flying in the clear in the vicinity of
a thunderstorm.
27.6 Current weather radar systems are able to
objectively determine precipitation intensity. These
precipitation intensity areas are described as “light,”
“moderate,” “heavy,” and “extreme.”
REFERENCE-
Pilot/Controller Glossary Term- Precipitation Radar Weather
Descriptions.
EXAMPLE-
Alert provided by an ATC facility to an aircraft:
(aircraft identification) EXTREME precipitation between
ten o'clock and two o'clock, one five miles. Precipitation
area is two five miles in diameter.
EXAMPLE-
Alert provided by an AFSS/FSS:
(aircraft identification) EXTREME precipitation two zero
miles west of Atlanta V-O-R, two five miles wide, moving
east at two zero knots, tops flight level three niner zero.
28. Thunderstorm Flying
28.1 Above all, remember this: never regard any
thunderstorm lightly, even when radar observers
report the echoes are of light intensity. Avoiding
thunderstorms is the best policy. Following are some
Do's and Don'ts of thunderstorm avoidance:
28.1.1 Don't land or takeoff in the face of an
approaching thunderstorm. A sudden gust front of
low-level turbulence could cause loss of control.
28.1.2 Don't attempt to fly under a thunderstorm
even if you can see through to the other side.
Turbulence and wind shear under the storm could be
disastrous.
28.1.3 Don't fly without airborne radar into a cloud
mass containing scattered embedded thunderstorms.
Scattered thunderstorms not embedded usually can
be visually circumnavigated.
28.1.4 Don't trust the visual appearance to be a
reliable indicator of the turbulence inside a
thunderstorm.
28.1.5 Do avoid by at least 20 miles any
thunderstorm identified as severe or giving an intense
radar echo. This is especially true under the anvil of
a large cumulonimbus.
28.1.6 Do clear the top of a known or suspected
severe thunderstorm by at least 1,000 feet altitude for
each 10 knots of wind speed at the cloud top.
However, the altitude capability of most aircraft
make it unlikely that the aircraft will be able to clear
the storm top.
28.1.7 Do circumnavigate the entire area if the area
has 6/10 thunderstorm coverage.
28.1.8 Do remember that vivid and frequent
lightning indicates the probability of a severe
thunderstorm.
28.1.9 Do regard as extremely hazardous any
thunderstorm that tops 35,000 feet or higher whether
the top is visually sighted or determined by radar.
28.2 If you cannot avoid penetrating a thunderstorm,
before entering the storm, you should do the
following:
28.2.1 Tighten your safety belt, put on your shoulder
harness if you have one, and secure all loose objects.
28.2.2 Plan and hold your course to take you through
the storm in a minimum time.
28.2.3 To avoid the most critical icing, establish a
penetration altitude below the freezing level or above
the level of -15 C.
28.2.4 Verify that pitot heat is on and turn on
carburetor heat or jet engine anti-ice. Icing can be
rapid at any altitude and cause almost instantaneous
power failure and/or loss of airspeed indication.
28.2.5 Establish power settings for turbulence
penetration airspeed recommended in your aircraft
manual.
28.2.6 Turn up cockpit lights to highest intensity to
lessen danger of temporary blindness from lightning.
28.2.7 If using automatic pilot, disengage altitude
hold mode and speed hold mode. The automatic
altitude and speed controls will increase maneuvers
of the aircraft thus increasing structural stresses.
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28.2.8 If using airborne radar, tilt the antenna up and
down occasionally. This will permit you to detect
other thunderstorm activity at altitudes other than the
one being flown.
28.3 Following are some Do's and Don'ts during the
thunderstorm penetration:
28.3.1 Do keep your eyes on your instruments.
Looking outside the cockpit can increase danger of
temporary blindness from lightning.
28.3.2 Don't change power settings; maintain
settings for the recommended turbulence penetration
airspeed.
28.3.3 Don't attempt to maintain constant altitude;
let the aircraft “ride the waves.”
28.3.4 Don't turn back once you are in the
thunderstorm. A straight course through the storm
most likely will get you out of the hazards more
quickly. In addition, turning maneuvers increase
stress on the aircraft.
29. Wake Turbulence
29.1 General
29.1.1 Every aircraft generates a wake while in
flight. Initially, when pilots encountered this wake in
flight, the disturbance was attributed to “prop wash.”
It is known, however, that this disturbance is caused
by a pair of counterrotating vortices trailing from the
wing tips. The vortices from larger aircraft pose
problems to encountering aircraft. For instance, the
wake of these aircraft can impose rolling moments
exceeding the roll control authority of the encounter-
ing aircraft. Further, turbulence generated within the
vortices can damage aircraft components and
equipment if encountered at close range. The pilot
must learn to envision the location of the vortex wake
generated by larger (transport category) aircraft and
adjust the flight path accordingly.
29.1.2 During ground operations and during takeoff,
jet engine blast (thrust stream turbulence) can cause
damage and upsets if encountered at close range.
Exhaust velocity versus distance studies at various
thrust levels have shown a need for light aircraft to
maintain an adequate separation behind large turbojet
aircraft. Pilots of larger aircraft should be particularly
careful to consider the effects of their “jet blast” on
other aircraft, vehicles, and maintenance equipment
during ground operations.
29.2 Vortex Generation
29.2.1 Lift is generated by the creation of a pressure
differential over the wing surface. The lowest
pressure occurs over the upper wing surface and the
highest pressure under the wing. This pressure
differential triggers the roll up of the airflow aft of the
wing resulting in swirling air masses trailing
downstream of the wing tips. After the roll up is
completed, the wake consists of two counter rotating
cylindrical vortices. Most of the energy is within a
few feet of the center of each vortex, but pilots should
avoid a region within about 100 feet of the vortex
core. (See FIG GEN 3.5-16.)
29.3 Vortex Strength
29.3.1 The strength of the vortex is governed by the
weight, speed, and shape of the wing of the generating
aircraft. The vortex characteristics of any given
aircraft can also be changed by extension of flaps or
other wing configuring devices as well as by change
in speed. However, as the basic factor is weight, the
vortex strength increases proportionately. Peak
vortex tangential speeds up to almost 300 feet per
second have been recorded. The greatest vortex
strength occurs when the generating aircraft is
HEAVY, CLEAN, and SLOW.
29.3.2 Induced Roll
29.3.2.1 In rare instances, a wake encounter could
cause inflight structural damage of catastrophic
proportions. However, the usual hazard is associated
with induced rolling moments which can exceed the
roll control authority of the encountering aircraft. In
flight experiments, aircraft have been intentionally
flown directly up trailing vortex cores of larger
aircraft. It was shown that the capability of an aircraft
to counteract the roll imposed by the wake vortex
primarily depends on the wing span and counter-con-
trol responsiveness of the encountering aircraft.
29.3.2.2 Counter-control is usually effective and
induced roll minimal in cases where the wing span
and ailerons of the encountering aircraft extend
beyond the rotational flow field of the vortex. It is
more difficult for aircraft with short wing span
(relative to the generating aircraft) to counter the
imposed roll induced by vortex flow. Pilots of
short-span aircraft, even of the high-performance
type, must be especially alert to vortex encounters.
(See FIG GEN 3.5-17.)
29.3.2.3 The wake of larger aircraft requires the
respect of all pilots.
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29.4 Vortex Behavior
29.4.1 Trailing vortices have certain behavioral
characteristics which can help a pilot visualize the
wake location and thereby take avoidance precau-
tions.
29.4.1.1 Vortices are generated from the moment
aircraft leave the ground, since trailing vortices are a
by-product of wing lift. Prior to takeoff or touchdown
pilots should note the rotation or touchdown point of
the preceding aircraft. (See FIG GEN 3.5-18.)
29.4.1.2 The vortex circulation is outward, upward
and around the wing tips when viewed from either
ahead or behind the aircraft. Tests with large aircraft
have shown that the vortices remain spaced a bit less
than a wing span apart, drifting with the wind, at
altitudes greater than a wing span from the ground. In
view of this, if persistent vortex turbulence is
encountered, a slight change of altitude and lateral
position (preferably upwind) will provide a flight
path clear of the turbulence.
29.4.1.3 Flight tests have shown that the vortices
from larger (transport category) aircraft sink at a rate
of several hundred feet per minute, slowing their
descent and diminishing in strength with time and
distance behind the generating aircraft. Atmospheric
turbulence hastens breakup. Pilots should fly at or
above the preceding aircraft's flight path, altering
course as necessary to avoid the area behind and
below the generating aircraft. However, vertical
separation of 1,000 feet may be considered safe.
(See FIG GEN 3.5-19.)
FIG GEN 3.5-16
Wake Vortex Generation
FIG GEN 3.5-17
Wake Encounter Counter Control
COUNTER
CONTROL
FIG GEN 3.5-18
Wake Ends/Wake Begins
Touchdown Rotation
Wake Ends Wake Begins
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FIG GEN 3.5-19
Vortex Flow Field
AVOID
Nominally 500-1000 Ft.
Sink Several Ft.,/Rate
Hundred Min.
FIG GEN 3.5-20
Vortex Movement Near Ground - No Wind
No Wind
3K 3K
29.4.1.4 When the vortices of larger aircraft sink
close to the ground (within 100 to 200 feet), they tend
to move laterally over the ground at a speed of 2 or
3_knots. (See FIG GEN 3.5-20.)
29.4.1.5 There is a small segment of the aviation
community that have become convinced that wake
vortices may “bounce” up to twice their nominal
steady state height. With a 200-foot span aircraft, the
“bounce” height could reach approximately 200 feet
AGL. This conviction is based on a single
unsubstantiated report of an apparent coherent
vortical flow that was seen in the volume scan of a
research sensor. No one can say what conditions
cause vortex bouncing, how high they bounce, at
what angle they bounce, or how many times a vortex
may bounce. On the other hand, no one can say for
certain that vortices never “bounce.” Test data have
shown that vortices can rise with the air mass in which
they are embedded. Wind shear, particularly, can
cause vortex flow field “tilting.” Also, ambient
thermal lifting and orographic effects (rising terrain
or tree lines) can cause a vortex flow field to rise.
Notwithstanding the foregoing, pilots are reminded
that they should be alert at all times for possible wake
vortex encounters when conducting approach and
landing operations. The pilot has the ultimate
responsibility for ensuring appropriate separations
and positioning of the aircraft in the terminal area to
avoid the wake turbulence created by a preceding
aircraft.
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FIG GEN 3.5-21
Vortex Movement Near Ground - with Cross Winds
6K
(3K + 3K)
3K Wind
0 (3K - 3K)
FIG GEN 3.5-22
Vortex Movement in Ground Effect - Tailwind
Light Quartering
Tailwind
x
Tail Wind
Touchdown Point
29.4.2 A crosswind will decrease the lateral
movement of the upwind vortex and increase the
movement of the downwind vortex. Thus a light wind
with a cross-runway component of 1 to 5 knots could
result in the upwind vortex remaining in the
touchdown zone for a period of time and hasten the
drift of the downwind vortex toward another runway.
(See FIG GEN 3.5-21.) Similarly, a tailwind condi-
tion can move the vortices of the preceding aircraft
forward into the touchdown zone. THE LIGHT
QUARTERING TAILWIND REQUIRES MAXI-
MUM CAUTION. Pilots should be alert to larger
aircraft upwind from their approach and takeoff flight
paths. (See FIG GEN 3.5-22.)
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29.5 Operations Problem Areas
29.5.1 A wake encounter can be catastrophic. In
1972 at Fort Worth, Texas, a DC-9 got too close to a
DC-10 (two miles back), rolled, caught a wingtip,
and cartwheeled coming to rest in an inverted
position on the runway. All aboard were killed.
Serious and even fatal general aviation accidents
induced by wake vortices are not uncommon.
However, a wake encounter is not necessarily
hazardous. It can be one or more jolts with varying
severity depending upon the direction of the
encounter, weight of the generating aircraft, size of
the encountering aircraft, distance from the generat-
ing aircraft, and point of vortex encounter. The
probability of induced roll increases when the
encountering aircraft's heading is generally aligned
with the flight path of the generating aircraft.
29.5.2 AVOID THE AREA BELOW AND
BEHIND THE GENERATING AIRCRAFT,
ESPECIALLY AT LOW ALTITUDE WHERE
EVEN A MOMENTARY WAKE ENCOUNTER
COULD BE HAZARDOUS. This is not easy to do.
Some accidents have occurred even though the pilot
of the trailing aircraft had carefully noted that the
aircraft in front was at a considerably lower altitude.
Unfortunately, this does not ensure that the flight path
of the lead aircraft will be below that of the trailing
aircraft.
29.5.3 Pilots should be particularly alert in calm
wind conditions and situations where the vortices
could:
29.5.3.1 Remain in the touchdown area.
29.5.3.2 Drift from aircraft operating on a nearby
runway.
29.5.3.3 _Sink into the takeoff or landing path from a
crossing runway.
29.5.3.4 Sink into the traffic pattern from other
airport operations.
29.5.3.5 Sink into the flight path of VFR aircraft
operating on the hemispheric altitude 500 feet below.
29.5.4 Pilots of all aircraft should visualize the
location of the vortex trail behind larger aircraft and
use proper vortex avoidance procedures to achieve
safe operation. It is equally important that pilots of
larger aircraft plan or adjust their flight paths to
minimize vortex exposure to other aircraft.
29.6 Vortex Avoidance Procedures
29.6.1 Under certain conditions, airport traffic
controllers apply procedures for separating IFR
aircraft. If a pilot accepts a clearance to visually
follow a preceding aircraft, the pilot accepts
responsibility for separation and wake turbulence
avoidance. The controllers will also provide to VFR
aircraft, with whom they are in communication and
which in the tower's opinion may be adversely
affected by wake turbulence from a larger aircraft, the
position, altitude and direction of flight of larger
aircraft followed by the phrase “CAUTION - WAKE
TURBULENCE.” After issuing the caution for wake
turbulence, the airport traffic controllers generally do
not provide additional information to the following
aircraft unless the airport traffic controllers know the
following aircraft is overtaking the preceding
aircraft. WHETHER OR NOT A WARNING OR
INFORMATION HAS BEEN GIVEN, HOWEVER,
THE PILOT IS EXPECTED TO ADJUST AIR-
CRAFT OPERATIONS AND FLIGHT PATH AS
NECESSARY TO PRECLUDE SERIOUS WAKE
ENCOUNTERS. When any doubt exists about
maintaining safe separation distances between
aircraft during approaches, pilots should ask the
control tower for updates on separation distance and
aircraft groundspeed.
29.6.2 The following vortex avoidance procedures
are recommended for the various situations:
29.6.2.1 Landing Behind a Larger Aircraft_-
Same Runway. Stay at or above the larger aircraft's
final approach flight path - note its touchdown point
- land beyond it.
29.6.2.2 Landing Behind a Larger Aircraft_-
When a Parallel Runway is Closer Than
2,500_Feet. Consider possible drift to your runway.
Stay at or above the larger aircraft's final approach
flight path_-_note its touchdown point.
29.6.2.3 Landing Behind a Larger Aircraft_-
Crossing Runway. Cross above the larger aircraft's
flight path.
29.6.2.4 Landing Behind a Departing Larger
Aircraft_-_Same Runway. Note the larger aircraft's
rotation point_-_land well prior to rotation point.
29.6.2.5 Landing Behind a Departing Larger
Aircraft_-_Crossing Runway. Note the larger
aircraft's rotation point_-_if past the
intersection_-_continue the approach_-_land prior to
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the intersection. If larger aircraft rotates prior to the
intersection, avoid flight below the larger aircraft's
flight path. Abandon the approach unless a landing is
ensured well before reaching the intersection.
29.6.2.6 Departing Behind a Larger Aircraft.
Note the larger aircraft's rotation point_-_rotate prior
to larger aircraft's rotation point_-_continue climb
above the larger aircraft's climb path until turning
clear of the larger aircraft's wake. Avoid subsequent
headings which will cross below and behind a larger
aircraft. Be alert for any critical takeoff situation
which could lead to a vortex encounter.
29.6.2.7 Intersection Takeoffs_-_Same Runway.
Be alert to adjacent larger aircraft operations,
particularly upwind of your runway. If intersection
takeoff clearance is received, avoid subsequent
headings which will cross below a larger aircraft's
path.
29.6.2.8 Departing or Landing After a Larger
Aircraft Executing a Low Approach, Missed
Approach, Or Touch-and-go Landing. Because
vortices settle and move laterally near the ground, the
vortex hazard may exist along the runway and in your
flight path after a larger aircraft has executed a low
approach, missed approach, or a touch-and-go
landing, particular in light quartering wind condi-
tions. You should ensure that an interval of at least
2_minutes has elapsed before your takeoff or landing.
29.6.2.9 En Route VFR (Thousand-foot Altitude
Plus 500 Feet). Avoid flight below and behind a
large aircraft's path. If a larger aircraft is observed
above on the same track (meeting or overtaking)
adjust your position laterally, preferably upwind.
29.7 Helicopters
29.7.1 In a slow hover-taxi or stationary hover near
the surface, helicopter main rotor(s) generate
downwash producing high velocity outwash vortices
to a distance approximately three times the diameter
of the rotor. When rotor downwash hits the surface,
the resulting outwash vortices have behavioral
characteristics similar to wing tip vortices produced
by fixed-wing aircraft. However, the vortex
circulation is outward, upward, around, and away
from the main rotor(s) in all directions. Pilots of small
aircraft should avoid operating within three rotor
diameters of any helicopter in a slow hover-taxi or
stationary hover. In forward flight, departing or
landing helicopters produce a pair of strong,
high-speed trailing vortices similar to wing tip
vortices of larger fixed-wing aircraft. Pilots of small
aircraft should use caution when operating behind or
crossing behind landing and departing helicopters.
29.8 Pilot Responsibility
29.8.1 Government and industry groups are making
concerted efforts to minimize or eliminate the
hazards of trailing vortices. However, the flight
disciplines necessary to ensure vortex avoidance
during VFR operations must be exercised by the pilot.
Vortex visualization and avoidance procedures
should be exercised by the pilot using the same degree
for concern as in collision avoidance.
29.8.2 Wake turbulence may be encountered by
aircraft in flight as well as when operating on the
airport movement area.
29.8.3 Pilots are reminded that in operations
conducted behind all aircraft, acceptance of instruc-
tions from ATC in the following situations is an
acknowledgment that the pilot will ensure safe
takeoff and landing intervals and accepts the
responsibility of providing his/her own wake
turbulence separation:
29.8.3.1 Traffic information.
29.8.3.2 Instructions to follow an aircraft.
29.8.3.3 The acceptance of a visual approach
clearance.
29.8.4 For operations conducted behind heavy
aircraft, ATC will specify the word “heavy” when this
information is known. Pilots of heavy aircraft should
always use the word “heavy” in radio communica-
tions.
29.8.5 Heavy and large jet aircraft operators should
use the following procedures during an approach to
landing. These procedures establish a dependable
baseline from which pilots of in-trail, lighter aircraft
may reasonably expect to make effective flight path
adjustments to avoid serious wake vortex turbulence.
29.8.5.1 Pilots of aircraft that produce strong wake
vortices should make every attempt to fly on the
established glidepath, not above it; or, if glidepath
guidance is not available, to fly as closely as possible
to a “3-1” glidepath, not above it.
EXAMPLE-
Fly 3,000 feet at 10 miles from touchdown, 1,500 feet at
5_miles, 1,200 feet at 4 miles, and so on to touchdown.
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29.8.5.2 Pilots of aircraft that produce strong wake
vortices should fly as closely as possible to the
approach course centerline or to the extended
centerline of the runway of intended landing as
appropriate to conditions.
29.8.6 Pilots operating lighter aircraft on visual
approaches in-trail to aircraft producing strong wake
vortices should use the following procedures to assist
in avoiding wake turbulence. These procedures apply
only to those aircraft that are on visual approaches.
29.8.6.1 Pilots of lighter aircraft should fly on or
above the glidepath. Glidepath reference may be
furnished by an ILS, by a visual approach slope
system, by other ground-based approach slope
guidance systems, or by other means. In the absence
of visible glidepath guidance, pilots may very nearly
duplicate a 3-degree glideslope by adhering to the
“3_to 1” glidepath principle.
EXAMPLE-
Fly 3,000 feet at 10 miles from touchdown, 1,500 feet at
5_miles, 1,200 feet at 4 miles, and so on to touchdown.
29.8.6.2 If the pilot of the lighter following aircraft
has visual contact with the preceding heavier aircraft
and also with the runway, the pilot may further adjust
for possible wake vortex turbulence by the following
practices:
a) Pick a point of landing no less than 1,000 feet
from the arrival end of the runway.
b) Establish a line-of-sight to that landing point
that is above and in front of the heavier preceding
aircraft.
c) When possible, note the point of landing of the
heavier preceding aircraft and adjust point of
intended landing as necessary.
EXAMPLE-
A puff of smoke may appear at the 1,000-foot markings of
the runway, showing that touchdown was at that point;
therefore, adjust point of intended landing to the
1,500-foot markings.
d) Maintain the line-of-sight to the point of
intended landing above and ahead of the heavier
preceding aircraft; maintain it to touchdown.
e) Land beyond the point of landing of the
preceding heavier aircraft.
29.8.7 During visual approaches pilots may ask ATC
for updates on separation and groundspeed with
respect to heavier preceding aircraft, especially when
there is any question of safe separation from wake
turbulence.
29.9 Air Traffic Wake Turbulence Separations
29.9.1 Because of the possible effects of wake
turbulence, controllers are required to apply no less
than specified minimum separation for aircraft
operating behind a heavy jet and, in certain instances,
behind large nonheavy aircraft; i.e., B757 aircraft.
29.9.1.1 Separation is applied to aircraft operating
directly behind a heavy and/or B757 jet at the same
altitude or less than 1,000 feet below:
a) Heavy jet behind heavy jet-4 miles.
b) Large/heavy behind B757 - 4 miles.
c) Small behind B757-5 miles.
d) Small/large aircraft behind heavy jet - 5_miles.
29.9.1.2 Also, separation, measured at the time the
preceding aircraft is over the landing threshold, is
provided to small aircraft:
a) Small aircraft landing behind heavy
jet_-_6_miles.
b) Small aircraft landing behind B757 -_5_miles.
c) Small aircraft landing behind large air-
craft_-_4_miles.
NOTE-
Aircraft classes are listed in the Pilot/Controller Glossary
in the Aeronautical Information Manual.
29.9.1.3 Additionally, appropriate time or distance
intervals are provided to departing aircraft. Two
minutes or the appropriate 4 or 5 mile radar separation
when takeoff behind a heavy/B757 jet will be:
a) From the same threshold.
b) On a crossing runway and projected flight paths
will cross.
c) From the threshold of a parallel runway when
staggered ahead of that of the adjacent runway by less
than 500 feet and when the runways are separated by
less than 2,500 feet.
NOTE-
Controllers may not reduce or waive these intervals.
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29.9.2 A 3-minute interval will be provided for a
small aircraft taking off:
29.9.2.1 From an intersection on the same runway
(same or opposite direction) behind a departing large
aircraft.
29.9.2.2 In the opposite direction on the same
runway behind a large aircraft takeoff or low/missed
approach.
NOTE-
This 3-minute interval may be waived upon specific pilot
request.
29.9.3 A 3-minute interval will be provided for all
aircraft taking off when the operations are as
described in paragraph 29.9.2 above, the preceding
aircraft is a heavy and/or a B757 jet, and the
operations are on either the same runway or parallel
runways separated by less than 2,500 feet.
Controllers may not reduce or waive this interval.
29.9.4 Pilots may request additional separation;
i.e.,_2_minutes instead of 4 or 5 miles for wake
turbulence avoidance. This request should be made as
soon as practical on ground control and at least before
taxiing onto the runway.
NOTE-
Federal Aviation Administration Regulations state: “The
pilot in command of an aircraft is directly responsible for
and is the final authority as to the operation of that
aircraft.”
29.9.5 Controllers may anticipate separation and
need not withhold a takeoff clearance for an aircraft
departing behind a large/heavy aircraft if there is
reasonable assurance the required separation will
exist when the departing aircraft starts takeoff roll.
30. International Civil Aviation
Organization (ICAO) Weather Formats
30.1 The U.S. uses the ICAO world standard for
aviation weather reporting and forecasting. The
utilization of terminal forecasts affirms U.S.
commitment to a single global format for aviation
weather. The World Meteorological Organization's
(WMO) publication No. 782, “Aerodrome Reports
and Forecasts,” contains the base METAR and TAF
code as adopted by the WMO member countries.
30.2 Although the METAR code is adopted
worldwide, each country is allowed to make
modifications or exceptions to the code for use in
their particular country; e.g., the U.S. will continue to
use statute miles for visibility, feet for RVR values,
knots for wind speed, inches of mercury for altimetry,
and will continue reporting prevailing visibility
rather than lowest sector visibility. A METAR report
contains the following sequence of elements in the
following order:
30.2.1 Type of report.
30.2.2 ICAO station identifier.
30.2.3 Date and time of report.
30.2.4 Modifier (as required).
30.2.5 Wind.
30.2.6 _Visibility.
30.2.7 Runway Visual Range (RVR).
30.2.8 Weather phenomena.
30.2.9 Sky conditions.
30.2.10 Temperature/Dew point group.
30.2.11 Altimeter.
30.2.12 Remarks (RMK).
30.3 The following paragraphs describe the
elements in a METAR report.
30.3.1 Type of Report. There are two types of
reports:
30.3.1.1 The METAR, an aviation routine weather
report.
30.3.1.2 The SPECI, a nonroutine (special) aviation
weather report.
The type of report (METAR or SPECI) will always
appear as the lead element of the report.
30.3.2 ICAO Station Identifier. The METAR code
uses ICAO 4-letter station identifiers. In the
contiguous 48 states, the 3-letter domestic station
identifier is prefixed with a “K”; i.e., the domestic
identifier for Seattle is SEA while the ICAO identifier
is KSEA. For Alaska, all station identifiers start with
“PA”; for Hawaii, all station identifiers start with
“PH.” The identifier for the eastern Caribbean is “T”
followed by the individual country's letter;
i.e.,_Puerto Rico is “TJ.” For a complete worldwide
listing see ICAO Document 7910, “Location
Indicators.”
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30.3.3 Date and Time of Report. The date and
time the observation is taken are transmitted as a
six-digit date/time group appended with Z to denote
Coordinated Universal Time (UTC). The first
two_digits are the date followed with two digits for
hour and two digits for minutes.
EXAMPLE-
172345Z (the 17th day of the month at 2345Z)
30.3.4 Modifier (As Required). “AUTO” identi-
fies a METAR/SPECI report as an automated weather
report with no human intervention. If “AUTO” is
shown in the body of the report, the type of sensor
equipment used at the station will be encoded in the
remarks section of the report. The absence of
“AUTO” indicates that a report was made manually
by an observer or that an automated report had human
augmentation/backup. The modifier “COR” indi-
cates a corrected report that is sent out to replace an
earlier report with an error.
NOTE-
There are two types of automated stations, AO1 for
automated weather reporting stations without a
precipitation discriminator, and AO2 for automated
stations with a precipitation discriminator. (A precipitation
discriminator can determine the difference between liquid
and frozen/freezing precipitation). This information
appears in the remarks section of an automated report.
30.3.5 Wind. The wind is reported as a five digit
group (six digits if speed is over 99 knots). The first
three digits are the direction from which the wind is
blowing, in tens of degrees referenced to true north,
or “VRB” if the direction is variable. The next two
digits is the wind speed in knots, or if over 99 knots,
the next three digits. If the wind is gusty, it is reported
as a “G” after the speed followed by the highest gust
reported. The abbreviation “KT” is appended to
denote the use of knots for wind speed.
EXAMPLE-
13008KT - wind from 130 degrees at 8 knots
08032G45KT - wind from 080 degrees at 32 knots with
gusts to 45 knots
VRB04KT - wind variable in direction at 4 knots
00000KT - wind calm
210103G130KT - wind from 210 degrees at 103 knots with
gusts to 130 knots
If the wind direction is variable by 60 degrees or more and
the speed is greater than 6 knots, a variable group
consisting of the extremes of the wind direction separated
by a “V” will follow the prevailing wind group.
32012G22KT 280V350
30.3.5.1 Peak Wind. Whenever the peak wind
exceeds 25 knots, “PK WND” will be included in
Remarks; e.g., PK WND 280045/1955 “Peak wind
two eight zero at four five occurred at one niner five
five.” If the hour can be inferred from the report time,
only the minutes will be appended; e.g., PK WND
34050/38 “Peak wind three four zero at five zero
occurred at three eight past the hour.”
30.3.5.2 Wind Shift. Whenever a wind shift
occurs, “WSHFT” will be included in remarks
followed by the time the wind shift began; e.g.,
WSHFT 30 FROPA “Wind shift at three zero due to
frontal passage.”
30.3.6 Visibility. Prevailing visibility is reported in
statute miles with “SM” appended to it.
EXAMPLE-
7SM seven statute miles . . . . . . . . .
15SM fifteen statute miles . . . . . . . .
1
/2SM one-half statute mile . . . . . . . .
30.3.6.1 Tower/Surface Visibility. If either tower
or surface visibility is below 4 statute miles, the lesser
of the 2 will be reported in the body of the report; the
greater will be reported in remarks.
30.3.6.2 Automated Visibility. ASOS visibility
stations will show visibility ten or greater than ten
miles as “10SM.” AWOS visibility stations will show
visibility less than 1
/4 statute mile as “M 1
/4SM” and
visibility ten or greater than ten miles as “10SM.”
30.3.6.3 Variable Visibility. Variable visibility is
shown in remarks when rapid increase or decrease by
1
/2 statute mile or more and the average prevailing
visibility is less than 3 statute miles; e.g., VIS 1V2
means “visibility variable between 1 and 2 statute
miles.”
30.3.6.4 Sector Visibility. Sector visibility is
shown in remarks when it differs from the prevailing
visibility, and either the prevailing or sector visibility
is less than 3 statute miles.
EXAMPLE-
VIS N2 visibility north two . . . . . . .
30 AUG 07
AIP
United States of America
GEN 3.5-62
15 MAR 07
Federal Aviation Administration Nineteenth Edition
30.3.7 Runway Visual Range (when reported).
“R” identifies the group followed by the runway
heading (and parallel runway designator, if needed)
“/” and the visual range in feet (meters in other
countries) followed with “FT.” (“Feet” is not
spoken.)
30.3.7.1 Variability Values. When RVR varies by
more than on reportable value, the lowest and highest
values are shown with “V” between them.
30.3.7.2 Maximum/Minimum Range. “P” indi-
cates an observed RVR is above the maximum value
for this system (spoken as “more than”). “M”
indicates an observed RVR is below the minimum
value which can be determined by the system (spoken
as “less than”).
EXAMPLE-
R32L/1200FT - Runway Three Two Left R-V-R one
thousand two hundred
R27R/M1000V4000FT - Runway Two Seven Right R-V-R
variable from less than one thousand to four thousand.
30.3.8 Weather Phenomena. In METAR, weather
is reported in the format:
Intensity / Proximity / Descriptor /
Precipitation / Obstruction to Visibility /
Other
NOTE-
The “/” above and in the following descriptions (except as
the separator between the temperature and dew point) are
for separation purposes in this publication and do not
appear in the actual METARs.
30.3.8.1 Intensity applies only to the first type of
precipitation reported. A “-” denotes light, no symbol
denotes moderate, and a “+” denotes heavy.
30.3.8.2 Proximity applies to and is reported only
for weather occurring in the vicinity of the airport
(between 5 and 10 miles of the point(s) of
observation). It is denoted by the letters “VC.”
(Intensity and “VC” will not appear together in the
weather group.)
30.3.8.3 Descriptor. These eight descriptors apply
to the precipitation or obstructions to visibility:
TS thunderstorm
DR low drifting
SH showers
MI shallow
FZ freezing
BC patches
BL blowing
PR partial
NOTE-
Although “TS” and “SH” are used with precipitation and
may be preceded with an intensity symbol, the intensity still
applies to the precipitation not the descriptor.
30.3.8.4 Precipitation. There are nine types of
precipitation in the METAR code:
RA rain
DZ drizzle
SN snow
GR hail (1
/4_ or greater)
GS small hail/snow pellets
PL ice pellets
SG snow grains
IC ice crystals
UP unknown precipitation (automated
stations only)
EXAMPLE-
TSRA thunderstorm with moderate rain
+SN heavy snow
-RA FG light rain and fog
BRHZ mist and haze (visibility 5
/8 mile or
greater)
FZDZ freezing drizzle
VCSH rain shower in the vicinity
+SHRASNPL heavy rain showers, snow, ice pellets
(Intensity indicator refers to the
predominant rain.)
30 AUG 07
AIP
United States of America
GEN 3.5-63
15 MAR 07
Federal Aviation Administration Nineteenth Edition
30.3.8.5 Obstructions to Visibility. Obscurations
are any phenomena in the atmosphere, other than
precipitation, that reduce horizontal visibility. There
are eight types of obscuration phenomena in the
METAR code:
FG fog (visibility less than 5
/8 mile)
HZ haze
FU smoke
PY spray
BR mist (visibility 5
/8-6 miles)
SA sand
DU dust
VA volcanic ash
NOTE-
Fog (FG) is observed or forecast only when the visibility is
less than 5
/8 mile. Otherwise, mist (BR) is observed or
forecast.
30.3.8.6 Other. There are five categories of other
weather phenomena which are reported when they
occur:
SQ squall
SS sandstorm
DS duststorm
PO dust/sand whirls
FC
+FC
funnel cloud
tornado/waterspout
30.3.9 Sky Condition. In METAR, sky condition is
reported in the format:
Amount / Height / (Type) or Indefinite Ceiling /
Height
30.3.9.1 Amount. The amount of sky cover is
reported in eighths of sky cover, using contractions:
SKC clear (no clouds)
FEW >0
/8 to 2
/8 cloud cover
SCT scattered (3
/8 to 4
/8 cloud cover)
BKN broken (5
/8 to 7
/8 cloud cover)
OVC overcast (8
/8 cloud cover)
CB cumulonimbus when present
TCU towering cumulus when present
NOTE-
1. “SKC” will be reported at manual stations. “CLR” will
be used at automated stations when no clouds below
12,000 feet are reported.
2. A ceiling layer is not designated in the METAR code.
For aviation purposes, the ceiling is the lowest broken or
overcast layer, or vertical visibility into obscuration. Also,
there is no provision for reporting thin layers in the METAR
code. When clouds are thin, that layer shall be reported as
if it were opaque.
30.3.9.2 Height. Cloud bases are reported with
three digits in hundreds of feet. (Clouds above 12,000
feet cannot be reported by an automated station.)
30.3.9.3 Type. If towering cumulus clouds (TCU)
or cumulonimbus clouds (CB) are present, they are
reported after the height which represents their base.
EXAMPLE-
SCT025TCU BKN080 BKN250 - “two thousand five
hundred scattered towering cumulus, ceiling eight
thousand broken, two five thousand broken.”
SCT008 OVC012CB - “eight hundred scattered ceiling
one thousand two hundred overcast cumulonimbus
clouds.”
30.3.9.4 Vertical Visibility (indefinite ceiling
height). The height into an indefinite ceiling is
preceded by “VV” and followed by three digits
indicating the vertical visibility in hundreds of feet.
This layer indicates total obscuration.
EXAMPLE-
1
/8 SM FG VV006 - visibility one eighth, fog, indefinite
ceiling six hundred.
30.3.9.5 Obscurations are reported when the sky is
partially obscured by a ground-based phenomena by
indicating the amount of obscuration as FEW, SCT,
BKN followed by three zeros (000). In remarks, the
obscuring phenomenon precedes the amount of
obscuration and three zeros.
EXAMPLE-
BKN000 (IN BODY) - “sky partially obscured.”
FU BKN000 (IN REMARKS) - “smoke obscuring five- to
seven-eighths of the sky.”
30.3.9.6 When sky conditions include a layer aloft
other than clouds, such as smoke or haze, the type of
phenomena, sky cover, and height are shown in
remarks.
30 AUG 07
AIP
United States of America
GEN 3.5-64
15 MAR 07
Federal Aviation Administration Nineteenth Edition
EXAMPLE-
BKN020 (IN BODY) - “ceiling two thousand broken.”
RMK FU BKN020 - “broken layer of smoke aloft, based at
two thousand.”
30.3.9.7 Variable Ceiling. When a ceiling is below
three thousand and is variable, the remark “CIG” will
be shown followed with the lowest and highest
ceiling heights separated by a “V.”
EXAMPLE-
CIG 005V010 - “ceiling variable between five hundred
and one thousand.”
30.3.9.8 Second Site Sensor. When an automated
station uses meteorological discontinuity sensors,
remarks will be shown to identify site specific sky
conditions which differ and are lower than conditions
reported in the body.
EXAMPLE-
CIG 020 RY11 - “ceiling two thousand at Runway One
One.”
30.3.9.9 Variable Cloud Layer. When a layer is
varying in sky cover, remarks will show the
variability range. If there is more than one cloud
layer, the variable layer will be identified by
including the layer height.
EXAMPLE-
SCT V BKN - “scattered layer variable to broken.”
BKN025 V OVC - “broken layer at two thousand five
hundred variable to overcast.”
30.3.9.10 Significant Clouds. When significant
clouds are observed, they are shown in remarks,
along with the specified information as shown below:
a) Cumulonimbus (CB), or Cumulonimbus Mam-
matus (CBMAM), distance (if known), direction
from the station, and direction of movement, if
known. If the clouds are beyond 10 miles from the
airport, DSNT will indicate distance.
EXAMPLE-
CB W MOV E - “cumulonimbus west moving east.”
CBMAM DSNT S - “cumulonimbus mammatus distant
south.”
b) Towering Cumulus (TCU), location, (if
known), or direction from the station.
EXAMPLE-
TCU OHD - “towering cumulus overhead.”
TCU W - “towering cumulus west.”
c) Altocumulus Castellanus (ACC), Stratocumu-
lus Standing Lenticular (SCSL), Altocumulus
Standing Lenticular (ACSL), Cirrocumulus Standing
Lenticular (CCSL) or rotor clouds, describing the
clouds (if needed), and the direction from the station.
ACC W “altocumulus castellanus
west”
ACSL SW-S “standing lenticular
altocumulus southwest
through south”
APRNT ROTOR CLD S “apparent rotor cloud
south”
CCSL OVR E “standing lenticular
cirrocumulus over the
east”
30.3.10 Temperature/Dew Point. Temperature
and dew point are reported in two, two-digit groups
in degrees Celsius, separated by a solidus (/).
Temperatures below zero are prefixed with an “M.”
If the temperature is available but the dew point is
missing, the temperature is shown followed by a
solidus. If the temperature is missing, the group is
omitted from the report.
EXAMPLE-
15/08 “temperature one five, dew point 8” . . . . . . . .
00/M02 “temperature zero, dew point minus 2” . . . . . . .
M05/ “temperature minus five, dew point . . . . . . . . .
missing”
30.3.11 Altimeter. Altimeter settings are reported
in a four-digit format in inches of mercury prefixed
with an “A” to denote the units of pressure.
EXAMPLE-
A2995 “altimeter two niner niner five” . . . . . . . .
30.3.12 Remarks. Remarks will be included in all
observations, when appropriate. The contraction
“RMK” denotes the start of the remarks section of a
METAR report.
Location of a phenomena within 5 statute miles of the
point of observation will be reported as at the station.
Phenomena between 5 and 10 statute miles will be
reported in the vicinity, “VC.” Phenomena beyond
10_statute miles will be shown as distant, “DSNT.”
Distances are in statute miles except for automated
lightning remarks which are in nautical miles.
Movement of clouds or weather will be indicated by
the direction toward which the phenomena is moving.
30 AUG 07
AIP
United States of America
GEN 3.5-65
15 MAR 07
Federal Aviation Administration Nineteenth Edition
There are two categories of remarks: Automated,
Manual, and Plain Language; and Additive and
Automated Maintenance Data.
30.3.12.1 Automated, Manual, and Plain Lan-
guage Remarks. This group of remarks may be
generated from either manual or automated weather
reporting stations and generally elaborates on
parameters reported in the body of the report. Plain
language remarks are only provided by manual
stations.
1) Volcanic Eruptions
2) Tornado, Funnel Cloud, Waterspout
3) Type of Automated Station (AO1 or AO2)
4) Peak Wind
5) Wind Shift
6) Tower or Surface Visibility
7) Variable Prevailing Visibility
8) Sector Visibility
9) Visibility at Second Location
10) Dispatch Visual Range
11) Lightning (freq) LTG (type) (loc)
12) Beginning/Ending Time of Precipitation
13) Beginning/Ending Time of Thunderstorms
14) Thunderstorm Location; Movement Direction
15) Hailstone Size
16) Virga
17) Variable Ceiling
18) Obscurations
19) Variable Sky Condition
20) Significant Cloud Types
21) Ceiling Height at Second Location
22) Pressure Rising or Falling Rapidly
23) Sea-Level Pressure
24) Aircraft Mishap (not transmitted)
25) No SPECI Reports Taken
26) Snow Increasing Rapidly
27) Other Significant Information
30.3.12.2 Additive and Automated Maintenance
Data Remarks.
1) Hourly Precipitation
2) Precipitation Amount
3) 24-Hour Precipitation
4) Snow Depth on Ground
5) Water Equivalent of Snow on Ground
6) Cloud Types
7) Duration of Sunshine
8) Hourly Temperature and Dew Point (Tenths)
9)_6-Hour Maximum Temperature
10)_6-Hour Minimum Temperature
11) 24-Hour Maximum/Minimum Temperatures
12)_Pressure Tendency
13)_Sensor Status:
WINO
ZRANO
SNO
VRNO
PNO
VISNO
EXAMPLE-
METAR report and explanation:
METAR KSFO 041453Z AUTO VRB02KT 3SM BR CLR
15/12 A3012 RMK AO2
METAR Type of report (aviation routine weather
report)
KSFO Station identifier (San Francisco, CA)
041453Z Date/Time (4th day of month; time
1453_UTC)
AUTO Fully automated; no human intervention
VRB02KT Wind (wind variable at two)
3SM Visibility (visibility three statute miles)
BR Visibility obscured by mist
CLR No clouds below one two thousand
15/12 Temperature one five; dew point one
two
A3012 Altimeter three zero one two
RMK Remarks
AO2 This automated station has a weather
discriminator (for precipitation).
30 AUG 07
AIP
United States of America
GEN 3.5-66
15 MAR 07
Federal Aviation Administration Nineteenth Edition
EXAMPLE-
METAR report and explanation:
METAR KBNA 281250Z 33018KT 290V360 1/2SM
R31/2700FT SN BLSN FG VV008 00/M03 A2991 RMK
RAE42SNB42
METAR Aviation routine weather report
KBNA Nashville, TN
281250Z 28th day of month; time 1250 UTC
(no modifier) This is a manually generated report,
due to the absence of “AUTO” and
“AO1 or AO2” in remarks.
33018KT Wind three three zero at one eight
290V360 Wind variable between two nine zero
and three six zero
1
/2SM Visibility one half statute mile
R31/2700FT Runway three one RVR two thousand
seven hundred feet
SN Moderate snow
BLSN FG Visibility obscured by blowing snow
and fog
VV008 Indefinite ceiling eight hundred
00/M03 Temperature zero; dew point minus
three
A2991 Altimeter two niner niner one
RMK Remarks
RAE36 Rain ended at three six
SNB42 Snow began at four two
EXAMPLE-
SPECI report and explanation:
SPECI KCVG 152224Z 28024G36KT 3/4SM +TSRA
BKN008 OVC020CB 28/23 A3000 RMK TSRAB24 TS W
MOV E.
SPECI Nonroutine aviation special weather
report
KCVG Cincinnati, OH
152224Z 15th day of month; time 2224 UTC
(no modifier) This is a manually generated report
due to the absence of “AUTO” and
“AO1 or AO2” in remarks.
28024G36KT Wind two eight zero at two four gusts
three six
3/4SM Visibility three fourths statute mile
+TSRA Thunderstorms, heavy rain
BKN008 Ceiling eight hundred broken
OVC020CB Two thousand overcast cumulonim-
bus clouds
28/23 Temperature two eight; dew point two
three
A3000 Altimeter three zero zero zero
RMK Remarks
TSRAB24 Thunderstorm and rain began at two
four
TS W MOV E Thunderstorm west moving east
30 AUG 07
AIP
United States of America
GEN 3.5-67
15 MAR 07
Federal Aviation Administration Nineteenth Edition
30.4 Aerodrome Forecast (TAF). A concise state-
ment of the expected meteorological conditions at an
airport during a specified period (usually 24 hours).
TAFs use the same codes as METAR weather reports.
They are scheduled four times daily for 24-hour
periods beginning at 0000Z, 0600Z, 1200Z, and
1800Z. TAFs are issued in the following format:
Type of Report / ICAO Station Identifier / Date
and Time of Origin / Valid Period Date and
Time / Forecast Meteorological Conditions
NOTE-
The “/” above and in the following descriptions are for
separation purposes in this publication and do not appear
in the actual TAFs.
30.4.1 Explanation of TAF elements
30.4.1.1 Type of Report. There are two types of
TAF issuances, a routine forecast issuance (TAF) and
an amended forecast (TAF AMD). An amended TAF
is issued when the current TAF no longer adequately
describes the on-going weather or the forecaster feels
the TAF is not representative of the current or
expected weather. Corrected (COR) or delayed
(RTD) TAFs are identified only in the communica-
tions header which precedes the actual forecasts.
30.4.1.2 ICAO Station Identifier. The TAF code
uses ICAO 4-letter location identifiers as described
in the METAR section.
30.4.1.3 Date and Time of Origin. This element is
the date and time the forecast is actually prepared.
The format is a two-digit date and four-digit time
followed, without a space, by the letter “Z.”
30.4.1.4 Valid Period Date and Time. The UTC
valid period of the forecast is a two-digit date
followed by the two-digit beginning hour and
two-digit ending hour. In the case of an amended
forecast, or a forecast which is corrected or delayed,
the valid period may be for less than 24 hours. Where
an airport or terminal operates on a part-time basis
(less than 24 hours/day), the TAFs issued for those
locations will have the abbreviated statement “NIL
AMD SKED AFT (closing time) Z” added to the end
of the forecasts. For the TAFs issued while these
locations are closed, the word “NIL” will appear in
place of the forecast text. A delayed (RTD) forecast
will then be issued for these locations after two
complete observations are received.
30.4.1.5 Forecast Meteorological Conditions.
This is the body of the TAF. The basic format is:
Wind / Visibility / Weather / Sky Condition /
Optional Data (Wind Shear)
The wind, visibility, and sky condition elements are
always included in the initial time group of the
forecast. Weather is included only if significant to
aviation. If a significant, lasting change in any of the
elements is expected during the valid period, a new
time period with the changes is included. It should be
noted that with the exception of an “FM” group, the
new time period will include only those elements
which are expected to change; i.e., if a lowering of the
visibility is expected but the wind is expected to
remain the same, the new time period reflecting the
lower visibility would not include a forecast wind.
The forecast wind would remain the same as in the
previous time period.
Any temporary conditions expected during a specific
time period are included with that time period. The
following describes the elements in the above format.
a) Wind. This five (or six) digit group includes
the expected wind direction (first 3 digits) and speed
(last 2 digits or 3 digits if 100 knots or greater). The
contraction “KT” follows to denote the units of wind
speed. Wind gusts are noted by the letter “G”
appended to the wind speed followed by the highest
expected gust.
NOTE-
A variable wind direction is noted by “VRB” where the
three digit direction usually appears. A calm wind (3 knots
or less) is forecast as “00000KT.”
EXAMPLE-
18010KT - wind one eight zero at one zero (wind is blowing
from 180 at 10 knots).
35012G20KT - wind three five zero at one two gust two
zero
b) Visibility. The expected prevailing visibility
up to and including 6 miles is forecast in statute miles,
including fractions of miles, followed by “SM” to
note the units of measure. Expected visibilities
greater than 6 miles are forecast as P6SM (Plus
six_statute miles).
EXAMPLE-
1/2SM visibility one-half . . . . . . . .
4SM visibility four . . . . . . . . .
P6SM visibility more than six . . . . . . . .
30 AUG 07
AIP
United States of America
GEN 3.5-68
15 MAR 07
Federal Aviation Administration Nineteenth Edition
c) Weather. The expected weather phenomena is
coded in TAF reports using the same format,
qualifiers, and phenomena contractions as METAR
reports (except UP).
Obscurations to vision will be forecast whenever the
prevailing visibility is forecast to be 6 statute miles or
less.
If no significant weather is expected to occur during
a specific time period in the forecast, the weather
group is omitted for that time period. If, after a time
period in which significant weather has been forecast,
a change to a forecast of no significant weather
occurs, the contraction NSW (no significant weather)
will appear as the weather group in the new time
period. (NSW is included only in becoming
(BECMG) or temporary (TEMPO) groups.)
d) Sky Condition. TAF sky condition forecasts
use the METAR format described in the METAR
section. Cumulonimbus clouds (CB) are the only
cloud type forecast in TAFs.
When clear skies are forecast, the contraction “SKC”
will always be used. The contraction “CLR” is never
used in the aerodrome forecast (TAF).
When the sky is obscured due to a surface-based
phenomenon, vertical visibility (VV) into the
obscuration is forecast. The format for vertical
visibility is “VV” followed by a three-digit height in
hundreds of feet.
NOTE-
As in METAR, ceiling layers are not designated in the TAF
code. For aviation purposes, the ceiling is the lowest
broken or overcast layer or vertical visibility into a
complete obscuration.
SKC “sky clear”
SCT005 BKN025CB “five hundred scattered,
ceiling two thousand five
hundred broken
cumulonimbus clouds”
VV008 “indefinite ceiling eight
hundred”
e) Optional Data (Wind Shear). Wind Shear is
the forecast of non-convective, low-level winds (up
to 2,000 feet). The forecast includes the letters “WS”
followed by the height of the wind shear, the wind
direction and wind speed at the indicated height and
the ending letters “KT” (knots). Height is given in
hundreds of feet (AGL) up to and including
2,000_feet. Wind shear is encoded with the
contraction “WS” followed by a three-digit height,
slant character “/” and winds at the height indicated
in the same format as surface winds. The wind shear
element is omitted if not expected to occur.
WS010/18040KT “low level wind shear at one
thousand, wind one eight
zero at four zero”
30.5 Probability Forecast. The probability or
chance of thunderstorms or other precipitation events
occurring, along with associated weather conditions
(wind, visibility, and sky conditions).
The PROB30 group is used when the occurrence of
thunderstorms or precipitation is 30-39 percent and
the PROB40 group is used when the occurrence of
thunderstorms or precipitation is 40-49 percent. This
is followed by a four-digit group giving the
beginning hour and ending hour of the time period
during which the thunderstorms or precipitation are
expected.
NOTE-
Neither PROB30 nor PROB40 will be shown during the
first six hours of a forecast.
EXAMPLE-
PROB40 2102 1/2SM +TSRA - “chance between 2100Z
and 0200Z of visibility one-half thunderstorm, heavy
rain.”
PROB30 1014 1SM RASN - “chance between 1000Z and
1400Z of visibility one rain and snow.”
30.6 Forecast Change Indicators. The following
change indicators are used when either a rapid,
gradual, or temporary change is expected in some or
all of the forecast meteorological conditions. Each
change indicator marks a time group within the TAF
report.
30.6.1 From (FM) Group. The FM Group is used
when a rapid change, usually occurring in less than
one hour, in prevailing conditions is expected.
Typically, a rapid change of prevailing conditions to
more or less a completely new set of prevailing
conditions is associated with a synoptic feature
passing through the terminal area (cold or warm
frontal passage). Appended to the “FM” indicator is
the four-digit hour and minute the change is expected
to begin and continues until the next change group or
until the end of the current forecast.
30 AUG 07
AIP
United States of America
GEN 3.5-69
15 MAR 07
Federal Aviation Administration Nineteenth Edition
An “FM” group marks the beginning of a new line in
a TAF report (indented 5 spaces). Each “FM” group
contains all the required elements-wind, visibility,
weather, and sky condition. Weather is omitted in
“FM” groups when it is not significant to aviation.
FM groups do not include the contraction NSW.
EXAMPLE-
FM0100 14010KT P6SM SKC - “after 0100Z, wind one
four zero at one zero, visibility more than six, sky clear.”
30.6.2 Becoming (BECMG) Group. The BECMG
group is used when a gradual change in conditions is
expected over a longer time period, usually
two_hours. The time period when the change is
expected is a four-digit group with the beginning
hour and ending hour of the change period which
follows the BECMG indicator. The gradual change
will occur at an unspecified time within this time
period. Only the changing forecast meteorological
conditions are included in BECMG groups. The
omitted conditions are carried over from the previous
time group.
EXAMPLE-
OVC012 BECMG 1416 BKN020 - “ceiling one thousand
two hundred overcast. Then a gradual change to ceiling
two thousand broken between 1400Z and 1600Z.”
30.6.3 Temporary (TEMPO) Group. The
TEMPO group is used for any conditions in wind,
visibility, weather, or sky condition which are
expected to last for generally less than an hour at a
time (occasional), and are expected to occur during
less than half the time period. The TEMPO indicator
is followed by a four-digit group giving the
beginning hour and ending hour of the time period
during which the temporary conditions are expected.
Only the changing forecast meteorological
conditions are included in TEMPO groups. The
omitted conditions are carried over from the previous
time group.
EXAMPLE-
1. SCT030 TEMPO 1923 BKN030 - “three thousand
scattered with occasional ceilings three thousand broken
between 1900Z and 2300Z.”
2. 4SM HZ TEMPO 0006 2SM BR HZ - “visibility four in
haze with occasional visibility two in mist and haze
between 0000Z and 0600Z.”
30 AUG 07
AIP
United States of America
GEN 3.5-70
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-23
U.S. Department
of Transportation
Federal Aviation
Administration
KEY to AERODROME FORECAST (TAF) and
AVIATION ROUTINE WEATHER REPORT
(METAR) (FRONT)
TAF KPIT 091730Z 091818 15005KT 5SM HZ FEW020 WS010/31022KT
FM 1930 30015G25KT 3SM SHRA OVC015 TEMPO 2022 1/2SM +TSRA
OVC008CB
FM0100 27008KT 5SM SHRA BKN020 OVC040 PROB40 0407 1SM -RA BR
FM1015 18005KT 6SM -SHRA OVC020 BECMG 1315 P6SM NSW SKC
METAR KPIT 091955Z COR 22015G25KT 3/4SM R28L/2600FT TSRA OVC010CB
18/16 A2992 RMK SLP045 T01820159
FORECAST EXPLANATION REPORT
TAF Message type : TAF-routine or TAF AMD-amended forecast,
METAR-hourly, SPECI-special or TESTM-non-commissioned
ASOS report
METAR
KPIT ICAO location indicator KPIT
091730Z Issuance time: ALL times in UTC “Z”, 2-digit date, 4-digit time 091955z
091818 Valid period: 2-digit date, 2-digit beginning, 2-digit ending times
In U.S. METAR: CORrected of; or AUTOmated ob for automated
report with no human intervention; omitted when observer logs on
COR
15005KT Wind: 3 digit true-north direction , nearest 10 degrees (or VaRiaBle);
next 2-3 digits for speed and unit, KT (KMH or MPS); as needed, Gust
and maximum speed; 00000KT for calm; for METAR, if direction varies
60 degrees or more, Variability appended, e.g. 180V260
22015G25KT
5SM Prevailing visibility; in U.S., Statute Miles & fractions; above 6 miles in
TAF Plus6SM. (Or, 4-digit minimum visibility in meters and as required,
lowest value with direction)
3/4SM
Runway Visual Range: R; 2-digit runway designator Left, Center, or
Right as needed; “/”, Minus or Plus in U.S., 4-digit value, FeeT in U.S.,
(usually meters elsewhere); 4-digit value Variability 4-digit value (and
tendency Down, Up or No change)
R28L/2600FT
HZ Significant present, forecast and recent weather: see table (on back) TSRA
FEW020 Cloud amount, height and type: Sky Clear 0/8, FEW >0/8-2/8,
SCaTtered 3/8-4/8, BroKeN 5/8-7/8, OVerCast 8/8; 3-digit height in
hundreds of ft; Towering Cumulus or CumulonimBus in METAR; in
TAF, only CB. Vertical Visibility for obscured sky and height “VV004”.
More than 1 layer may be reported or forecast. In automated METAR
reports only, CLeaR for “clear below 12,000 feet”
OVC 010CB
Temperature: degrees Celsius; first 2 digits, temperature “/” last 2
digits, dew-point temperature; Minus for below zero, e.g., M06
18/16
Altimeter setting: indicator and 4 digits; in U.S., A-inches and
hundredths; (Q-hectoPascals, e.g. Q1013)
A2992
30 AUG 07
AIP
United States of America
GEN 3.5-71
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-24
U.S. Department
of Transportation
Federal Aviation
Administration
KEY to AERODROME FORECAST (TAF) and
AVIATION ROUTINE WEATHER REPORT
(METAR) (BACK)
FORECAST EXPLANATION REPORT
WS010/31022KT In U.S. TAF, non-convective low-level (2,000 ft) Wind Shear;
3-digit height (hundreds of ft); “/”; 3-digit wind direction and 2-3
digit wind speed above the indicated height, and unit, KT
In METAR, ReMarK indicator & remarks. For example: Sea-
Level Pressure in hectoPascals & tenths, as shown: 1004.5 hPa;
Temp/dew-point in tenths _C, as shown: temp. 18.2_C, dew-point
15.9_C
RMK
SLP045
T01820159
FM1930 FroM and 2-digit hour and 2-digit minute beginning time:
indicates significant change. Each FM starts on a new line,
indented 5 spaces
TEMPO 2022 TEMPOrary: changes expected for <1 hour and in total, < half of
2-digit hour beginning and 2-digit hour ending time period
PROB40 0407 PROBability and 2-digit percent (30 or 40): probable condition
during 2-digit hour beginning and 2-digit hour ending time
period
BECMG 1315 BECoMinG: change expected during 2-digit hour beginning
and 2-digit hour ending time period
Table of Significant Present, Forecast and Recent Weather- Grouped in categories and used in the
order listed below; or as needed in TAF, No Significant Weather.
QUALIFIER
INTENSITY OR PROXIMITY
`-' Light “no sign” Moderate `+' Heavy
VC Vicinity: but not at aerodrome; in U.S. METAR, between 5 and 10SM of the point(s) of
observation; in U.S. TAF, 5 to 10SM from center of runway complex (elsewhere within 8000m)
DESCRIPTOR
MI Shallow BC Patches PR Partial TS Thunderstorm
BL Blowing SH Showers DR Drifting FZ Freezing
WEATHER PHENOMENA
PRECIPITATION
DZ Drizzle RA Rain SN Snow SG Snow grains
IC Ice Crystals PL Ice Pellets GR Hail GS Small hail/snow
UP Unknown precipitation in automated observations pellets
OBSCURATION
BR Mist (5/8SM) FG Fog (<5/8SM) FU Smoke VA Volcanic ash
SA Sand HZ Haze PY Spray DU Widespread dust
OTHER
SQ Squall SS Sandstorm DU Duststorm PO Well developed
FC Funnel cloud +FC tornado/waterspout dust/sand whirls
-Explanations in parentheses “( )” indicate different worldwide practices.
- Ceiling is not specified; defined as the lowest broken or overcast layer, or the vertical visibility.
- NWS TAFs exclude turbulence, icing & temperature forecasts; NWS METARs exclude trend forecasts
January 1999 Department of Transportation
Aviation Weather Directorate FEDERAL AVIATION ADMINISTRATION
30 AUG 07
AIP
United States of America
GEN 3.5-72
15 MAR 07
Federal Aviation Administration Nineteenth Edition
31. Meteorological Broadcasts (ATIS, VHF
and LF)
31.1 Continuous Transcribed Weather
Broadcasts (TWEB)
31.1.1 Weather broadcasts are made continuously
over selected navigational aids. These broadcasts
contain the general weather forecasts and winds up to
12,000_feet within a 250-mile radius of the radio. In
some cases the forecasts are for route of flight rather
than the general area. They also broadcast pilot
reports, radar reports, and hourly weather reports of
selected locations within a 400-mile radius of the
broadcast station.
31.2 Automatic Terminal Information Service
(ATIS) Broadcasts
31.2.1 These broadcasts are made continuously and
include as weather information only the ceiling,
visibility, wind, and altimeter setting of the
aerodrome at which they are located.
31.3 Scheduled Weather Broadcasts (SWB)
31.3.1 Scheduled broadcasts are made only in
Alaska at 15_minutes past the hour over en route
navigational aids not used for TWEB or ATIS. These
broadcasts contain hourly weather reports of selected
locations within 150 miles of the station and weather
advisories, pilot weather reports, radar weather
reports, and Notices to Airmen (NOTAMs).
31.4 Navigational Aids Providing Broadcast
Services
31.4.1 A compilation of navigational aids over
which weather broadcasts are transmitted is not
available for this publication. Complete information
concerning all navigational aids providing this
service is contained in the Airport/Facility directory.
Similar information for the Pacific and Alaskan areas
is contained in the Pacific and Alaska Supplements.
31.5 Hazardous Inflight Weather Advisory
Service (HIWAS)
31.5.1 A 24-hour continuous broadcast of hazard-
ous inflight weather is available on selected
navigational outlets. Broadcasts include: severe
weather forecast alerts (AWW), airman's meteoro-
logical information (AIRMET), significant meteoro-
logical information (SIGMET), Convective SIG-
MET (WST), urgent pilot weather reports (UUA),
hazardous portions of the domestic area forecasts
(FA), and center weather advisories (CWA). HIWAS
broadcast outlets are identified on en route/sectional
charts and in airport facility directories. For further
details, contact your nearest FSS.
30 AUG 07
AIP
United States of America
GEN 3.5-73
15 MAR 07
Federal Aviation Administration Nineteenth Edition
TBL GEN 3.5-11
Meteorological Broadcasts (VOLMET)
Name Call Sign Frequency Broadcast Form Contents Emission Remarks
Honolulu Honolulu Radio 2863, 6679,
8828, 13282
kHz
H00-05 and
H30-35
Forecasts PHNL Honolulu
PHTO Hilo
PGUM Guam
Voice Plain language
English
SIGMET Oakland FIR
Hourly Reports PHNL Honolulu
PHTO Hilo
PHOG Kahului
PGUM Guam
E05-10 and
E35-40
Hourly Reports KSFO San Francisco
KSEA Seattle
KLAX Los Angeles
KPDX Portland
KSMF Sacramento
KONT Ontario
KLAS Las Vegas
SIGMET Oakland FIR
Aerodrome
Forecasts
KSFO San Francisco
KSEA Seattle
KLAX Los Angeles
E25-30 and
E55-00
Hourly Reports PANC Anchorage
PAED ElmendorfAFB
PAFA Fairbanks
PACD Cold Bay
PAKN King Salmon
CYVR Vancouver
SIGMET Oakland FIR
Forecasts PANC Anchorage
PAFA Fairbanks
PACD Cold Bay
CYVR Vancouver
New York New York
Radio
3485, 6604,
10051, 13270
kHz
H00-05 Aerodrome
Forecasts
KDTW Detroit
KCLE Cleveland
KCVG Cincinnati
Voice Plain language
English
Hourly Reports KDTW Detroit
KCLE Cleveland
KCVG Cincinnati
KIND Indianapolis
KPIT Pittsburgh
H05-10 SIGMET Oceanic - New York
FIR
Aerodrome
Forecasts
KBGR Bangor
KBDL Windsor Locks
KCLT Charlotte
Hourly Reports KBGR Bangor
KBDL Windsor Locks
KORF Norfolk
KCLT Charlotte
H10-15 Aerodrome
Forecasts
KJFK New York
KEWR Newark
KBOS Boston
Hourly Reports KJFK New York
KEWR Newark
KBOS Boston
KBAL Baltimore
KIAD Washington
30 AUG 07
AIP
United States of America
GEN 3.5-74
15 MAR 07
Federal Aviation Administration Nineteenth Edition
Meteorological Broadcasts (VOLMET) - continued
Name Call Sign Frequency Broadcast Form Contents Emission Remarks
H15-20 SIGMET Oceanic - Miami
FIR/San Juan FIR
Aerodrome
Forecasts
MXKF Bermuda
KMIA Miami
KATL Atlanta
Hourly Reports MXKF Bermuda
KMIA Miami
MYNN Nassau
KMCO Orlando
KATL Atlanta
H30-35 Aerodrome
Forecasts
KORD Chicago
KMKE Milwaukee
KMSP Minneapolis
Hourly Reports KORD Chicago
KMKE Milwaukee
KMSP Minneapolis
KDTW Detroit
KBOS Boston
E35-40 SIGMET Oceanic - New York
FIR
Aerodrome
Forecasts
KIND Indianapolis
KSTL St. Louis
KPIT Pittsburgh
Hourly Reports KIND Indianapolis
KSTL St. Louis
KPIT Pittsburgh
KACY Atlantic City
E40-45 Aerodrome
Forecasts
KBAL Baltimore
KPHL Philadelphia
KIAD Washington
Hourly Reports KBAL Baltimore
KPHL Philadelphia
KIAD Washington
KJFK New York
KEWR Newark
E45-50 SIGMET Oceanic - Miami
FIR/San Juan FIR
Aerodrome
Forecasts
MYNN Nassau
KMCO Orlando
Hourly Reports MXKF Bermuda
KMIA Miami
MYNN Nassau
KMCO Orlando
KATL Atlanta
KTPA Tampa
KPBI West Palm
Beach
All stations operate on A3 emission H24.
All broadcasts are made 24 hours daily, seven days a week.
30 AUG 07
AIP
United States of America
GEN 3.5-75
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-25
Key to Decode an ASOS/AWSS (METAR) Observation (Front)
30 AUG 07
AIP
United States of America
GEN 3.5-76
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-26
Key to Decode an ASOS/AWSS (METAR) Observation (Back)
30 AUG 07
AIP
United States of America
GEN 3.5-77
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-27
NEXRAD Coverage
30 AUG 07
AIP
United States of America
GEN 3.5-78
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-28
NEXRAD Coverage
30 AUG 07
AIP
United States of America
GEN 3.5-79
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-29
NEXRAD Coverage
30 AUG 07
AIP
United States of America
GEN 3.5-80
15 MAR 07
Federal Aviation Administration Nineteenth Edition
FIG GEN 3.5-30
Volcanic Activity Reporting Form (VAR)
30 AUG 07
AIP
United States of America
GEN 3.6-1
15 MAR 07
Federal Aviation Administration Nineteenth Edition
GEN 3.6 Search and Rescue
1. Responsible Authority
1.1 The Search and Rescue (SAR) service in the U.S.
and its area of jurisdiction is organized in accordance
with the Standards and Recommended Practices of
ICAO Annex 12 by the Federal Aviation Administra-
tion with the collaboration of the U.S. Coast Guard
and the U.S. Air Force. The Coast Guard and the Air
Force are the responsible SAR authorities and have
the responsibility for making the necessary facilities
available. Postal and telegraphic addresses for the
Federal Aviation Administration are given in
GEN 3.1. The appropriate addresses for Coast Guard
and Air Force offices are:
Air Force
Postal Address:
Inland SAR Coordinator
Commander ARRS
USAF RCC
Tyndall AFB, FL
Telegraphic Address: None.
Telex: None.
Telephone: 1-800-851-3051,
Commercial: 850-283-5955, or
Defense Switching Network: 523-5955.
Coast Guard
Postal Address:
United States Coast Guard
Search and Rescue Division (GOSR/73)
400 7th Street, S.W.
Washington, D.C. 20590
Telegraphic Address: None.
Telex: 89 2427
2. Types of Service
2.1 Details of the Rescue Coordination Centers
(RCCs) and related rescue units are given in this
section. In addition, various elements of state and
local police organizations are available for search and
rescue missions when required. The aeronautical,
maritime and public telecommunication services are
available to the search and rescue organizations.
2.2 Aircraft, both land and amphibious based, are
used, as well as land and seagoing vessels, when
required, and carry survival equipment. Airborne
survival equipment, capable of being dropped,
consists of inflatable rubber dinghies equipped with
medical supplies, emergency rations and survival
radio equipment. Aircraft and marine craft are
equipped to communicate on 121.5, 123.1, 243.0,
500_kHz, 2182 kHz, and 8364 kHz. Ground rescue
teams are equipped to communicate on 121.5 MHz,
500_kHz, and 8364 kHz. SAR aircraft and marine
craft are equipped with direction finding equipment
and radar.
3. SAR Agreements
3.1 Bilateral agreements exist between the U.S. and
the following neighboring States of the NAM region:
Canada and Mexico.
3.1.1 There are two agreements with Canada. One
provides for public aircraft of either country which
are engaged in air search and rescue operations to
enter or leave either country without being subjected
to immigration or customs formalities normally
required. The other permits vessels and wrecking
appliances of either country to render aid and
assistance on specified border waters and on the
shores and in the waters of the other country along the
Atlantic and Pacific Coasts within a distance of
30_miles from the international boundary on those
coasts. A post operations report is required.
3.1.2 The agreement with Mexico applies to
territorial waters and shores of each country within
200 miles of the border on the Gulf Coast and within
270 miles of the border on the Pacific Coast. It
permits the vessels and aircraft of either country to
proceed to the assistance of a distressed vessel or
aircraft of their own registry upon notification of
entry and of departure of the applicable waters and
shores.
3.2 In situations not falling under the above
agreements, requests from States to participate in a
SAR operation within the U.S. for aircraft of their
own registry may be addressed to the nearest RCC.
The RCC would reply, and issue appropriate
instructions.
30 AUG 07
AIP
United States of America
GEN 3.6-2
15 MAR 07
Federal Aviation Administration Nineteenth Edition
4. General Conditions of Availability
4.1 The SAR service and facilities in the U.S. are
available to the neighboring States within the NAM,
NAT, CAR, PAC Regions upon request to the
appropriate RCC at all times when they are not
engaged in search and rescue activity in their home
territory. All facilities are specialized in SAR
techniques and functions.
