Aero-Tips!

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Aero-Tips 09.24.06

Need to steer around a cumulus build-up while on an Instrument Flight Rules (IFR) flight plan? Air Traffic Control (ATC) is usually quite willing to let you deviate as requested, if you ask in a way they understand and provide some basic information they can use to predict where you'll be so they can route you around other traffic.

Opening the exchange

I've found the best way to ask ATC for a deviation is to make a radio call like this:

"Kansas City Center, Bonanza 329PT request."

This lets the controller know I'm about to ask for something they have not anticipated from my clearance or flight plan information. Undoubtedly he/she will come back saying:

Nine Papa Tango, go ahead with your request.

Now I want to simply and succinctly let ATC know what I want to do. The Aeronautical Information Manual (AIM) says when asking for a deviation you should tell controllers:

1. Proposed point where detour will commence.
2. Proposed route and extent of detour (direction and distance).
3. Point where original route will be resumed.
4. Flight conditions (IFR or VFR).
5. Any further deviation that may become necessary as the flight progresses.
6. Advise if the aircraft is equipped with functioning airborne radar.

In reality what most pilots do is ask something like this:

"Nine Papa Tango needs to deviate ten degrees left of course"

Controllers will generally grant the deviation. The sooner you ask for the deviation the smaller heading change it'll take to fly around the cloud, and therefore the more likely ATC can accommodate your request.

Remember you are pilot-in-command. You do not need to enter a hazardous build-up just because you have not received approval for a deviation. If you must violate your clearance to avoid the hazard you may have to declare an emergency to have this authority-so don't wait too long before asking for a deviation.

It's helpful if you can, based on visual information or data in the cockpit, add something like:

"Nine Papa Tango will need to deviate left of course for about 20 miles."

This makes your revised route more predictable, so you're more likely to get the deviation you need.

Resume own navigation

Once past the towering cloud you'll need to advise ATC you can resume course. Usually you'll be told to "resume own navigation." This means to re-intercept your original flight path (airway, direct-to route) -- remember, that's the route ATC has cleared you around other traffic. Sometimes you'll be told to fly "direct" to the next fix on your clearance; with this directive you need not reintercept your original course before reaching the specified fix, but instead can go directly from your present, "deviated" position.

Aero-tip of the day: Know when and how to request a deviation from an IFR clearance.

FMI: Aero-Tips