We all know that the Nexrad weather graphics we see on our multifunction displays can be dangerously outdated, showing the location of storms not where they are now but where they were many minutes ago. But did you know that the precipitation data displayed on ARTCC radar scopes suffers from a similar lag? Maybe you haven’t given it much thought, but what a controller can see on his radar screen can lead to the same traps we’ve been taught to avoid when using downlink weather gear in our cockpits.
To minimize the impact of unwelcome weather surprises en route, plan well ahead for possible course deviations. Thunderstorms can develop rapidly – some have been recorded rising at rates exceeding 6,000 feet per minute. Obviously, if you encounter weather that puts the safety of your aircraft in jeopardy, declare an emergency so that you can exercise your authority to deviate immediately.
Also keep in mind that deteriorating weather disrupts the flow of all air traffic in the vicinity, and this increases workload demands on controllers. Requests for deviations around weather should be made as far in advance as possible to give controller’s advance notice, making it more likely that they will be able to approve your request.
When asking for approval to deviate around weather, the FAA’s Instrument Flying Handbook recommends including the following information in your call up:
1. The proposed point where the deviation will commence;
2. The proposed route and extent of the detour (direction and distance);
3. The point where the original route will be resumed;
4. The flight conditions you are encountering (i.e. IMC or VMC)
5. Whether the aircraft is equipped with functioning airborne radar; and
6. Any further deviation that may become necessary.
By making requests for deviations early, you greatly increase your chances of having your request granted while also ensuring that you won’t run into weather conditions that leave you with few good options.
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