One of the flight planning products I use frequently for FSX and X-Plane is SimBrief. If you're like me and have a navigraph subscription you can use the most current AIRAC cycle on the site; else you can still use -- for free -- the slightly outdated data. Being a flight sim grognard I prefer the current data, but the older data works just as well in most cases--especially if you're not using Vatsim / IVAO or PilotEdge.
This site will help you plan a realistic route and fuel requirements for 88 supported aircraft types (including a Twin Otter). It's a very capable alternative to PFPX, a payware flight planning utility.From the website:
Established in the spring of 2013, SimBrief.com was created with the intent of sharing a series of flight planning tools with the general Flight Simulation community. Aircraft performance and navigational databases are based on real world data, making SimBrief ideal for use with any of the Flight Simulation programs currently on the market.
Through a partnership with Navigraph, purchasers of Navigraph's FMS Data product can enjoy the added bonus of unlocking the latest AIRAC for use with their SimBrief account. That being said, those without a Navigraph subscription can still freely use the default SimBrief.com database, which is slightly dated.
The SimBrief dispatch system supports numerous different aircraft types. Currently, 88 total aircraft types are available, with more in the works!
Users should note that not all profiles are created equal. Most aircraft profiles are based on official manufacturer data and are highly accurate, however others may be less accurate due to a lack of available data. A full listing of available aircraft profiles, along with their respective features and level of accuracy can be found below.