Tuesday, March 12, 2013
Weather Avoidance Techniques
Staying Out of Trouble When it isn’t CAVU
There can be situations where takeoff is possible, but returning to the field won't be (cells on the approach path). In that case, you may want to identify a takeoff alternate in case problems develop during climbout.
Deviations around active cells can be worked out with ATC, based on information from whatever sensor you have —but if you're displaying on a multifunction display (MFD) and operating over anything other than flat terrain, you may want to periodically switch between the radar/data link/lightning display and terrain. You don't want to deviate around a cell and fly into a mountain!
As soon as you think a deviation may be needed, advise ATC, so that they can identify any conflicting traffic and approve or deny your request early.
With on-ship radar or lightning detectors, it's important to periodically switch to maximum range while working around local cells—otherwise, you might succeed in getting around a small problem and wind up face-to-face with a bigger one.
Thunderstorms are dynamic, and can build at rates of 5,000 FPM or higher. Thus, old data—from any sensor—can be worse than useless, tempting you to fly into areas that look clear, only to encounter a rapidly developing monster. If you're using data link, the only way to avoid this is to give all active areas a wide berth. With onboard radar, periodically checking shorter ranges may help. Lightning detectors will show any cells developed enough to produce lightning, but may not show building cells that haven't had time to develop significant electrical activity.
As you plan your approach, use whatever sensor you have to inspect weather not only at the destination airport, but also on your missed approach. If there's a cell near the missed approach hold you'll want to know about it and discuss what to do with ATC before beginning descent.
Understand the capabilities and limitations of whatever weather avoidance equipment you have, and you can fly safely when conditions are well below CAVU!
|For More Information|
|NTSB Safety Alert on NEXRAD Mosaic Imagery
Aeronautical Information Manual 7.1 (meteorology)
Airborne Radar Training Course (CD and online versions
Sirius XM Aviation Weather (data link)
Avidyne TWX670 Tactical Weather Detection System (lightning detector)
L-3 Avionics Systems Stormscope (lightning detector)
Insight Avionics Strike Finder (lightning detector)
Honeywell Bendix-King ART-2000 (on-board radar)
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