I second HercDriver130's comments. The weather in these destinations can change by the hour and the forecasts can be WAY off. Your divert options are limited to none (depending on the route you choose).
Just curious, how long can a 172 with 175 gallons stay airborne? I used a primitive distance calculator I found on google and the distance between St. Johns and Azores is roughly 1,200 miles. Assuming a ground speed of 250kts (not sure if thats even possible), thats about a 5:15 flight.
1. Before I did this flight, I would first make sure you are legal. I'd check each FIRs requirements.
NAT PCO has a lot of good info for the North Atlantic.
2. Customs requirements, etc. Landing fees? ATC fees?
3. I would first get an inspection done and make sure she is healthy. Then I would do a practice flight and keep her airborne as long as possible just to make sure she can go the distance.
4. Safety equipment. I would have all the necessary safety equipment. You will only last a few minutes in the North Atlantic this time of year. Radios, beacons, smoke, signals, exposure suit, small inflattable raft. You can probably rent these from somewhere.
5. Have a backup for your GPS. Also, what is your backup if you lose GPS signals? Its happened to me before in big airplanes and we have a minimum of two antennas.
6. Weather. What are the winds. Do you have the comm equipment to get hourly updates on your destinations? Do you have anti-ice de-ice equipment? Are there clouds at the altitude you're going to fly? Can you make it if you have to decend due to icing.
If I had to do this, I would pick the route that flew over land as much as possible. Below is a chart for VHF coverage at 10,000ft. You can find this and more at the link provided above.
-Fatty
