If you are flying VFR into deterioration weather conditions and would like to continue the flight under IFR, or you would like to climb to a better altitude but are restricted by a cloud layer, what is the easiest way to go about requesting and instrument clearance.
Assuming you are not already talking to ATC:
Houston Center, Cessna 1234X, request*
Cessna 34X, Houston Center, go ahead
Cessna 34X is a 172/U, 35 North IDU, 4500 ft, request IFR to Austin
Cessna 34X ident, fly heading 270
Cessna 34X is cleared to AUS via radar vectors, climb and maintain 6000 ft, squawk 5634
This is essentially the same as making a request for VFR flight following services with the exceptions:
- Your aircraft needs to be legal for IFR.
- You need to be rated and current for IFR.
- You will receive a clearance.
If you already have flight following and need IFR, the controller has you on his scope and already has a strip for you, and you just need to ask him to make you IFR. In that case he will just put you on an IFR altitude and give you a clearance limit and route.
*As noted in the comments, you may decorate this call with something identifying the nature of your request
There is an excellent article on AvWeb about Pop-Up IFR which goes into more about when pilots should ask for a pop-up IFR clearance. One of the most importatnt aspects is that if you are starting to get uncomfortable with the weather, or are being forced lower and lower, don't hesitate just because you aren't familiar with the proper procedure.
Obviously, you need to talk to ATC. Find a frequency on your charts or from FSS. If time is of the essence (you are in deteriorating VFR conditions and it's no better behind you) then ask for help on guard (121.5) rather than endangering yourself while looking for a frequency. If the weather has gotten so bad that you are no longer able to maintain VFR or can no longer maintain safe terrain clearance, then start climbing immediately and contact ATC as soon as possible for help and a clearance.
More than anything else, be clear when you are in need. Don't hesitate to declare an emergency if needed. They really want to help you in this situation! All of this applies, even if you aren't 100% legal for IFR flight if it can be done safely (i.e. just because your transponder hasn't received a 24 month inspection in time doesn't mean that you should just keep going lower until you end up clipping a tower).
All of that being said, asking for the clearance is done in pretty much the same way as asking for VFR flight following. Tell them who you are, where you are, and what you need. Their first priority when they get a request like this is to get you somewhere safe, and then they will ask you for additional information if they need it.