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Hello Everyone,

Spring is upon is and I want everyone to think of Thunderstorms, but do not forget about icing, every year, not just the bad years, we lose an airplane to Thunderstorms. Unfortunately the message does not get to everyone in the community, so please pass along some caution to all of your friends that fly high performance airplanes whether high time pilots or not. There are plenty of statistics with fatal accidents at the hands of pilots with over 10,000 hours as well as under 100 hours.

Over 25 percent of fatal weather-related General Aviation accidents are attributed to thunderstorms. To make matters worse, high performance aircraft often fly at altitudes that put them in the worst of weather.

The three thunderstorm categories based on causal source types are:

Air mass thunderstorms
Often occurring on warm afternoons in late Spring, Summer and early20Fall, air mass thunderstorms are the result of the sun’s heating of the earth’s surface and the resulting rising column of warm air. Often isolated, you may be able to maneuver around them.

Frontal thunderstorms
Caused by a cold front pushing into a warmer air mass with lots of moisture, frontal thunderstorms are difficult, if not impossible to circumnavigate.

Squall lines
Squall lines are often characterized by narrow bands of convection, heavy rainfall, and intense winds and shear. They usually occur ahead of a cold front.

Embedded thunderstorms
Embedded thunderstorms are thunderstorms hidden in solid masses of other clouds. These storms can sometimes be avoided by climbing on top of the cloud layer and watching for buildups, or by staying low (if ceilings and visibilities permit) and navigating around columns of rain. IMC Flight without thunderstorm detection ability and relying on datalink weather, which can have 1 hour 30 minute delays, can have fatal consequences. You need to have 100% knowledge that there are no embedded thunderstorms or turn around or land.

Radar works through line-of-sight, similar to a VOR. On the East coast, radar coverage is very good and the returns from altitudes at which thunderstorms develop is excellent. In mountainous areas the limitations of radar can be a factor. Because radar works through line-of-sight it cannot see over or around mountains. R adar sites located on mountaintops, which can be over 8,000 msl, may 'overshoot' precipitation. Keep in mind that a radar return with no precipitation echoes (no returns) does not mean that there is no significant weather, as clouds and fog are not detected by the radar. However, when echoes are present, turbulence can be implied by the intensity of the precipitation, and icing is implied by the presence of the precipitation at temperatures at or below zero degrees Celsius.

Regarding precipitation and turbulence, look at (or ask ATC) how far apart the different levels of precipitation are from each other. This difference is called the gradient. Just like with isobars—the closer they are together, the more turbulent the ride. Precipitation gradient is also a good indicator of turbulence. Rule of thumb: the closer the precipitation levels are together, the more turbulence expected.

For more information on thunderstorm avoidance and turbulence around convective activity, read section 7-1-29 of the AIM.

The following thunderstorm levels were established by the National Weather Service and are based on measurements from the Vid eo Integrator and Processor, or VIP. VIP contours radar reflectivity in dBZ.

New Terminology	dBZ	Rain Fall/Hour
Light	18-29	.01" to .10"
Moderate	30-40 =0 A	.175" to .50"
Heavy	40-50	.50" to 2.0"
Extreme	50+	2.0" to 16+"

During fair weather, Weather and Radar Processor, WARP receives NEXRAD updates every 9-11 minutes. When precipitation is detected NEXRAD automatically switches to "precipitation mode" and updates more frequently (Generally, at least every 4-6 minutes). WARP does NOT display light precipitation.

ATC's primary purpose is to separate IFR aircraft. Other services, such as VFR flight following and basic weather information, are provided on a workload-permitting basis.

Don't be confused by the terminology. Approach Control facilities and consolidated TRACONs offer the same services and have the same weather radar equipment.

One critical exception, however, is delay time. WARP can be up to 10-12 minutes old, where ASR approach controllers have near real time weather images. This difference, if relied on, could prove fatal.

Center Abbreviation	Center Name
ZAB	Albuquerque
ZAN	Anchorage
ZAU	Chicago
ZBW	Boston
ZDC	Washington
ZDV	Denver
ZFW	Dallas-Ft Worth
ZHN	Honolulu
ZHU	Houston
ZID	Indianapolis
ZJX	Jacksonville
ZKC	Kansas City
ZLA	Los Angeles
ZLC	Salt Lake City
ZMA	Miami
ZME	Memphis
ZMP	Minneapolis
ZNY	New York
ZOA	Oakland
ZOB	Cleveland
ZSE	Seattle
ZTL	Atlanta

As PIC you are responsible and need to be aware of FAR 91.123, PIC authority and how it relates to weather avoidance and other safety concerns:

Compliance with ATC clearances and instructions.
(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.

(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.

(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

(d) Each pilot in command who (though not deviating from a rule of this subpart) is given priority by ATC in an emergency, shall submit a detailed report of that emergency within 48 hours to the manager of that ATC facility, if requested by ATC.

(e) Unless otherwise authorized by ATC, no person operating an aircraft may operate that aircraft according to any clearance or instruction that has been issued to the pilot of another aircraft for radar air traffic control purposes.

FAA recommendations:

The Aeronautical Information Manual (AIM) section, 7-1-30 has information regarding thunderstorm avoidance. Below is an excerpt from the AIM.

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 thunderstorm. A sudden gust front of low level turbulence could cause loss of control.

2. Don't attempt to fly under a thunde rstorm 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 embedded 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 any thunderstorm by at least 20 miles.

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. This should exceed the altitude capability of most aircraft.

7. Do circumnavigate the entire area if the area has 6/10 thunderstorm coverage.

8. Do remember that vivid and frequent lightning indicates the probability of a strong thunderstorm.

9. Do regard as extremely hazardous any thunderstorm with tops 35,000 feet or=2 0higher whether the top is visually sighted or determined by radar.

10. Turn up cockpit lights to highest intensity to lessen temporary blindness from lightning.

11. 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 stress.

12. 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.

The FAA says:

If you cannot avoid penetrating a thunderstorm, following are some Do's before entering the storm:

1. Tighten your safety belt, put on your shoulder harness if you have one and secure all loose objects.

2. Plan and hold your course to take you through the storm in a minimum time.

3. To avoid the most critical icing, establish a penetration altitude below the freezing level or above the level of minus 15 degrees Celsius.

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.

5. Establish power settings for turbulence penetration airspeed recommended in your aircraft manual.

6. Turn up cockpit lights to highest intensity to lessen temporary blindness from lightning.

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 stress.