TM106101(8/01)
RDR-1600 Pilot’s Guide
53
Advisory Circulars (Cont.)
52
RDR-1600 Pilot’s Guide
TM106101(8/01)
Advisory Circulars (Cont.)
AC 00-24B
1/20/83
radar echoes depends on echo intensity, spacing between the echoes,
and the capabilities of you and your aircraft. Remember that weather
radar detects only precipitation drops; it does not detect turbulence.
Therefore, the radar scope provides no assurance of avoiding turbulence.
The radar scope also does not provide assurance of avoiding instrument
weather from clouds and fog. Your scope may be clear between intense
echoes; this clear area does not necessarily mean you can fly between
the storms and maintain visual sighting of them.
f. Remember that while hail always gives a radar echo, it may fall
several miles from the nearest visible cloud and hazardous turbulence
may extend to as much as 20 miles from the echo edge. Avoid intense or
extreme level echoes by at least 20 miles; that is, such echoes should be
separated by at least 40 miles before you fly between them. With weaker
echoes you can reduce the distance by which you avoid them.
7. DO'S AND DON'TS OF THUNDERSTORM FLYING.
a. 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:
(1) Don't land or takeoff in the face of an approaching thunder-
storm. A sudden gust front of low level turbulence could cause loss of
control.
(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.
(3) Don't fly without airborne radar into a cloud mass containing
scattered embedded thunderstorms. Scattered thunderstorms not embed-
ded usually can be visually circumnavigated.
(4) Don't trust the visual appearance to be a reliable indicator of the
turbulence inside a thunderstorm.
(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.
(6) Do circumnavigate the entire area if the area has 6/10 thunder-
storm coverage.
(7) Do remember that vivid and frequent lightning indicates the
probability of a severe thunderstorm.
(8) Do regard as extremely hazardous any thunderstorm with tops
35,000 feet or higher whether the top is visually sighted or determined by
radar.
AC 00-24B
1/20/83
during massive water ingestion. Although the exact mechanism of these
water-induced engine stalls has not bee determined, it is felt that thrust
changes may have an adverse effect on engine stall margins in the pres-
ence of massive water ingestion.
(3) Avoidance of severe storm systems is the only measure as-
sured to be effective in preventing exposure to this type of multiple engine
damage/flameout. During an unavoidable encounter with severe storms
with extreme precipitation, the best known recommendation is to follow
the severe turbulence penetration procedure contained in the approved
airplane flight manual with special emphasis on avoiding thrust changes
unless excessive airspeed variations occur.
6. WEATHER RADAR.
a. Weather radar detects droplets of precipitation size. Strength of the
radar return (echo) depends on drop size and number. The greater the
number of drops, the stronger is the echo; and the larger the drops, the
stronger is the echo. Drop size determines echo intensity to a much
greater extent that does drop number. Hailstones usually are covered with
a film of water and, therefore, act as huge water droplets giving the
strongest of all echoes.
b. Numerous methods have been used in an attempt to categorize the
intensity of a thunderstorm. To standardize thunderstorm language
between weather radar operators and pilots, the use of Video Integrator
Processor (VIP) levels is being promoted.
c. The National Weather Service (NWS) radar observer is able to
objectively determine storm intensity levels with VIP equipment. These
radar echo intensity levels are on a scale of one to six. If the maximum
VIP Levels are 1 "weak" and 2 "moderate," then light to moderate tur-
bulence is possible with lightning. VIP Level 3 is "strong" and severe tur-
bulence is possible with lightning. VIP Level 4 is "very strong" and severe
turbulence is likely with lightning. VIP Level 5 is "intense" with severe tur-
bulence, lightning, hail likely, and organized surface wind gusts. VIP Level
6 is "extreme' with severe turbulence, lightning, large hail, extensive sur-
face wind gusts, and turbulence.
d. Thunderstorms build and dissipate rapidly. Therefore, do not
attempt to plan a course between echoes. The best use of ground radar
information is to isolate general areas and coverage of echoes. You must
avoid individual storms from in-flight observations either by visual sighting
or by airborne radar. It is better to avoid the whole thunderstorm area than
to detour around individual storms unless they are scattered.
e. Airborne weather avoidance radar is, as its name implies, for avoid-
ing severe weather - not for penetrating it. Whether to fly into an area of
