Issue # 2001 - 3
*** SPECIAL EDITION *** Return to Air Traffic Publications Home Page
you hear that low, rumbling sound? You know what it is - it is the far
off growl of thunder, and chances are, it is headed your way. Just as
sure as the daffodils will bloom in the spring, the thunderheads will
blossom, too, and that is bad news for us. Why? Because those of us in
the safety business know that thunderstorms mean danger. Whether it is
called a microburst, low level wind shear, turbulence, hail, a
downdraft, or the worst of all scenarios, a funnel cloud, we know the
extra danger thunderstorms can produce. Year in and year out we are
faced with the same phenomena. You probably know exactly where the
storms will be when spring comes.
you do not know where the convective activity will be, it is time to
find out, before the boomers arrive. Thunderstorms are predictable
only in the sense that we know when conditions are right. Forecasters
can measure and observe the atmospheric conditions and say with
assurance only that storms might
form. We play a vital role in the confirmation of that forecast,
because we form a direct link to thousands of informal observers in
the sky: pilots. It is this source of data that we should take
advantage of as often as possible. Through the eyes of the pilot, we
can learn about the actual conditions aloft, whether a line is forming
or dissipating, whether lightning is cloud-to-cloud or
cloud-to-ground, whether the tops are building, static, or decreasing.
All of these elements contribute to our knowledge of the real
situation, and more knowledge for us increases the level of safety for
you work, convective activity has its own personality. Florida, for
example, is prone to "pop-up" type thunderstorms - storms
that build quickly and produce localized, violent weather. In the
Southwest, storms form in advance of a front or dry line, creating a
long, thin line of dangerous weather. Both of these situations call
for knowledge, vigilance, and experience on our part, and in each case
forecasters can say when conditions are right, but the confirmation,
the where and how big, the how fast, mean, ugly, and nasty might come
from you, and you only.
are dangerous, true, but we know how to deal with that danger. We use
weather radar. We use pilot weather reports (PIREP). FAAO 7110.65, Air
Traffic Control, paragraph 2-6-3, PIREP Information, says:
PIREP information includes reports of strong frontal activity, squall
lines, thunderstorms, light to severe icing, wind shear, and
turbulence (including clear air turbulence) of moderate or greater
intensity, volcanic eruptions and volcanic ash clouds, and other
conditions pertinent to flight safety. Solicit PIREP's when
requested or when one of the following conditions exists or is
forecast for your area of jurisdiction: ceilings at or below 5,000
feet, visibility (surface or aloft) at or less than 5 miles,
thunderstorms and related phenomena, turbulence of moderate degree or
greater, icing of light degree or greater, wind shear, volcanic ash
clouds, and for terminal facilities, when braking action advisories
are in effect.
we receive the PIREP's, relay the information to concerned aircraft in
a timely manner.
also use convective significant meteorological information (SIGMET),
forecasts, vectors, deviations and severe weather reroutes. We use
communication and coordination. But most of all, we use our judgment
and common sense. As well-trained professionals, we know where to
obtain a weather brief when we come on duty. We know how to broadcast
hazardous inflight weather advisory service (HIWAS) advisories for
airmen's meteorological information, SIGMET, and center weather
7110.65, Air Traffic Control, paragraph 2-6-2, HIWAS, says:
shall advise pilots of hazardous weather that may impact operations
within 150 NM of their sector or area of jurisdiction. Hazardous
weather information contained in HIWAS broadcasts includes Airmen's
Meteorological Information (AIRMET), SIGMET, Convective SIGMET (WST),
Urgent Pilot Weather Reports (UUA), and Center Weather Advisories (CWA).
Facilities shall review alert messages to determine the geographical
area and operational impact for hazardous weather information
broadcasts. The broadcast is not required if aircraft on your
frequency(s) will not be affected.
within commissioned HIWAS areas shall broadcast a HIWAS alert on all
frequencies, except emergency frequency, upon receipt of hazardous
weather information. Controllers are required to disseminate data
based on the operational impact on the sector or area of control
outside of commissioned HIWAS areas shall advise pilots of the
availability of hazardous weather advisories. Pilots requesting
additional information should be directed to contact the nearest
Flight Watch or Flight Service. Controllers
shall also apply the same procedure when HIWAS outlets, or outlets
with radio coverage extending into your sector or airspace under your
jurisdiction, are out of service.
that terminal facilities have the option to limit hazardous weather
information broadcasts as follows: Tower cab and approach control
facilities may opt to broadcast hazardous weather information alerts
only when any part of the area described is within 50 NM of the
airspace under their jurisdiction.
also know how to monitor Low Level Wind Shear Alert System and
Terminal Doppler Weather Radar (TDWR) and the phraseology for passing
warnings to pilots.
7110.65, Air Traffic Control, paragraph 3-1-8, Low Level Wind Shear
Advisories, states that when low level wind shear is reported by
pilots or detected on any of the Doppler or Low Level Wind Shear Alert
Systems (LLWAS), controllers shall issue the alert to all arriving and
departing aircraft until the alert is broadcast on the Automatic
Terminal Information Service (ATIS) and pilots indicate they have
received the appropriate ATIS code. A statement shall be
included on the ATIS for 20 minutes
following the last report or indication of wind shear.
"Network Expansion" (LLWAS III) and LLWAS systems that are
integrated with TDWR provide the capability of displaying microburst
alerts, wind shear alerts, and wind information oriented to the
threshold or departure end of a runway. TDWR is designed to detect
wind shear and microburst activity. The associated ribbon display
allows the controller to read the displayed alert without any need for
up on your procedures now, while it's quiet.
Listen. Do you hear the thunderstorms coming?
Flight into Terrain (CFIT) and Stabilized Approach Procedures.
CFIT is one of the greatest causes of accidents involving large
aircraft. In an effort to reduce CFIT, many flight instructors are now
emphasizing stabilized approach procedures when nonprecision
approaches are being executed. Stabilized
approach procedures are characterized by a constant angle - a constant
rate of descent approach profile ending near the touchdown point where
the landing maneuver begins. Complying with FAAO 7110.65, Air Traffic
Control, and good operating practices facilitates these procedures.
When low cloud ceilings exist, vector an aircraft so that it is
established on the final approach course at least two miles outside of
the approach gate at an altitude not above the glide slope/glidepath.
Additionally, for a nonprecision approach, place an aircraft at
an altitude that will allow descent in accordance with published
procedures facilitate stabilized approaches.
Slam dunks, dive and drive, and other procedures that require
abnormally high descent rates inhibit a pilot's ability to descend
toward the runway in a stabilized constant descent configuration.
These procedures can significantly increase pilot workload at a
critical phase of flight. (ATP-100)