Aviation Safety Corner

GREETINGS! For this monthís topic, I would like to conclude my discussion on "Thunderstorms." Nature may deal the cards, but ATC can help even the odds of winning an encounter. Now, Part IV of IV.

Letís begin with "Weather Resources." Coordinating the weather reports is the Aviation Weather Center in Kansas City, where SIGMETs (WS), AIRMETs (WA) and Area Forecasts (FA) originate. Area Forecasts are issued three times daily and cover a large geographical area. In-flight advisories such as SIGMETs and AIRMETs are issued as needed. SIGMETs warn of weather that is "significant to the safety of all aircraft."

Convective SIGMETs (WST) cover tornadoes, lines of thunderstorms, thunderstorms greater than level 4 with coverage of40% or more, embedded thunderstorms, and hail ¾-inch or greater. SIGMETs and AIRMETs cover weather that is progressively less severe. Listen also for Center Weather Advisories (CWA). These are unscheduled announcements of adverse weather. ATC will read a brief description of the advisory. If it sounds as though it will affect your flight, call Flight Service for the details.

Flight Watch on 122.0 is the easiest way to get weather, but if severe weather is widespread the frequency may be jammed with other pilots wanting information. Listen for a few minutes and you may glean what you need.

Convective SIGMETs also appear on the ATIS if they affect the area surrounding the airport. Try tuning in ATIS at airports ahead on your route. The ATIS wonít play the entire message, just a brief description, but if controllers arenít too busy theyíll read you the entire advisory and add information they have.

Advisories are broadcast on HIWAS, the Hazardous In-flight Weather Advisory Service. As the name implies, it describes hazardous weather and includes severe weather forecast alerts, AIRMETs, CWAs, unforecast weather and urgent PIREPS. Found on select VORs, they allow pilots to monitor the frequency without leaving ATC.

Transcribed Weather Broadcast. TWEB--is similar to HIWAS but issues weather in enroute format, such as,"--from Kansas City to Des Moines to Mason City." TWEBs, broadcast on select VORs and NDBs, are not limited to hazardous weather.

Now lets discuss, "Scud Runners." The pilot sees the runway or at least enough of the environment to feel confident. As both plane and storm coverage on the runway, the visibility and ceiling drops. Escape options close behind the pilot. About that time the altimeter tumbles and winds change from a nice head wind for the straight in to a momentary calm that lulls the pilot into feeling safe. Then the wind snaps around to a ferocious tailwind.

Sometimes the scud runner slams it on the runway with 20 knots of tailwind. Worse, the pilot must now circle to another runway as rain dumps, lightning flashes, and more chances build for disaster.

No one but the pilot-in-command can make the go/no go decision. ATC can warn of trouble, but few are the controllers who climb into the cockpit and take over the flight.

Thunderstorms are so complicated a weather phenomenon that many of their mechanisms remain unknown. We do know our aircraft are no match for the winds, rain, ice, hail, or turbulence associated with thunderstorms.

Despite technological improvements, plans and avoidance are still the best defenses. Personally, I would rather watch T-storms from the ground than flying into or around them. From the control tower the view is spectacular, particularly if no pilots are trying to steal the show.

Now, here are some helpful points if you ever encounter a T-Storm. Despite the best efforts of you, your equipment and ATC, there may well be a time when you fly into the belly of the beast. One of the biggest problems will be turbulence within the cell.

  1. Slow the aircraft to below the maneuvering speed for your airplane. Tighten your seat belt and secure loose objects.

  2. Set power to maintain levels altitude before entering the cell and leave it alone.

  3. Donít try to hold altitude. You may use the autopilot, but turn off the altitude hold and speed hold.

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

  5. Try to penetrate below the freezing level or above the -15 degree C level. Verify that pitot heat is on and, if applicable, carb heat.

  6. Turn all cockpit lights to maximum brightness. Keep your eyes on the instruments to minimize the possibility of temporary lightning-induced blindness.

  7. Maintain a constant attitude.

  8. Donít turn back.

  9. Fly the airplane. If that means having ATC calls go unanswered, so be it.

Now, in conclusion, REMEMBER, THUNDERSTORMS INCREASE PILOT AND CONTROLLER WORKLOAD. Cold Fact: PILOTíS are regularly killed trying to beat weather. Lesser-known fact: AIR TRAFFIC CONTROLLERS sweat bullets watching pilots trying to kill themselves. Itís too easy to get trapped. So donít even think about scud running.


Donít miss next monthís Aviation Safety Corner, When Iíll start a New Topic, "GASPING FOR GAS." Many fuel exhaustion accidents share three common mistakes. This will again be a Four Part Series.

See you at our Annual Christmas Banquet! SEASON GREETINGS! AND HAPPY NEW YEAR! SAFE FLYING!

Larry G. Harmon


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