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6. The Terminal Weather Information for
Pilots System (TWIP).
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 reduce air traffic controller workload.
With the TWIP capability, terminal weather
information, both alphanumerically and graphically,
is now available directly to the cockpit on a test basis
at 9 locations.
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.
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 five minutes for character graphic
messages. During good weather (below the predeter-
mined 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.
27. PIREPs Relating to Volcanic Ash
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 extremely 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. Additionally,
studies have shown that volcanic eruptions are the
only significant source of large quantities of sulphur
) gas at jet-cruising altitudes. Therefore,
the detection and subsequent reporting of SO
significant importance. Although SO
is colorless, its
presence in the atmosphere should be suspected when
a sulphur-like or rotten egg odor is present throughout
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 or detection of sulphur
) gas associated with volcanic activity.
Pilots should submit PIREPs regarding volcanic
activity using the Volcanic Activity Reporting (VAR)
not immediately available, relay enough information
to identify the position and type of volcanic activity.
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.
Turbulence, hail, rain, snow, lightning, sus-
tained updrafts and downdrafts, icing conditions−all
are 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.
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