Airplane ferry tank installation.
To increase range for Atlantic or Pacific ferry flights, airplane ferry tanks can be installed in most general aviation aircraft. Ferry tanks are typically 1-time use only and require both a ferry permit (special airworthiness certificate) and an overweight permit. For Atlantic ferry flights, a ferry tank with FAA and Transport Canada approval can be installed in Bangor, usually in 1-2 days. For Pacific ferry flights to Hawaii and Australia, ferry tanking is available on the West Coast.
Airplanes with 800 nm range or more don't need ferry tanking to cross the North Atlantic. Along the Northern route via Greenland and Iceland, there are several options for fuel stops, and if your airplane has at least 800 nm range you can safely cross the North Atlantic via the far Northern route. See the section on Atlantic ferry flight routes for more detail.
For Atlantic crossings in aircraft with less than 800 nautical mile range, ferry tanking is the best option. Also, for Atlantic ferry flights in a slower aircraft during the winter months, ferry tanking may be a good option to be able to fly along the Southern route to the Azores and Portugal.
I only fly with approved ferry tank installations done by experienced shops. I typically prefer not to use ferry tanks, unless I am flying a North Atlantic ferry flight in an aircraft such as Cessna 172, Piper Archer or Cessna 206, which have limited range.