Page 23 - Volume 18 Number 8

If, after selecting MAP mode, the echo is still three- colored, it’s a Level 4 or greater storm. How much greater? Go back to WX mode and reduce the CAL control (mislabeled GAIN on most radars) to the halfway position between CAL (or MAX) and MIN. If the echo is now only green and yellow, it’s Level 4. If you still see red, it’s Level 5 or greater. Again, check the chart for the potential hazards. (Check with your radar to make certain reducing CAL works for you. And be aware this assumes a GA radar; some airliner radars are different animals.)Now, about realistic avoidance distances. For hazard avoidance considerations, be conservative. At lower altitudes, less than 15,000 feet, if you determine it’s only Level 3, just fly well clear of all clouds attached to it. If Level 4, avoid by a minimum of three or four miles. At Level 5 or greater, severe to extreme turbulence can be expected out to 10 to 20 nm from the entire echo, green included, extending on out another 10 nm or so into the black areas surrounding the echo. Large hail is possible to as much as 20 nm away from the entire echo, particularly on the downwind side, relative to 20,000 foot and above winds. Add another 20 nm on the anvil side.Be as safe as schedule and conditions allow. In terminal areas, don’t fall into the follow-the-leader trap. Make your own decisions. At higher levels, where there’s more room for circumnavigation, for Levels 3 or 4, five nautical miles minimum on the upwind side, 10 to 15 on the downwind side. Level 5 or greater, 20 nm on the upwind side; on the downwind side by a distance equal to winds in the flight levels.And stay clear of stratus-appearing clouds connected with thunderstorms when up at altitude. That may require you to change altitudes, but it’s always best to be above or below cloud decks for visibility and potential engine icing considerations. If you think or have heard that wet clouds don’t exist above 30,000 feet, it’s a lie.Those distances are conservative, but chances are you’re not on•a rigid schedule. Treat your passengers to a smooth, relaxing flight. Deviate. You’ll enjoy the flight more as well. T&TYour Source for King Air Landing GearTrace AviationQuarter Page4/C Ad• Inspect • Overhaul • Exchange • Install• CompleteShipSets• KingAirAircraftMaintenance601-936-3599 • www.traceaviation.comMr. Trammell’s credentials are 33 years as an instructor and lecturer on airborne weather radar and convective storms avoidance. His clients have included most major airlines, all five military services and numerous government agencies, including the FAA, NASA and NTSB.His research has been exhaustive and has included more than 4,000 hours of inflight thunderstorm research, both in his own aircraft and from the jump seat for airline clients. He’s a pilot and CFII, with much twin and turbine experi- ence. His monthly web site, www.radar4pilots.com, has been up monthly since May, 2005.AUGUST 2014TWIN & TURBINE • 21