Starting in the Air

To start FlightGear in the air, you need at a minimum to set the following:

• the altitude in feet MSL, using the altitude option
• the calibrated airspeed, using the vc option (or alternately, the Mach number, using the mach option)

You can also set the heading using the heading option, but note that the heading is in degrees true rather than degrees magnetic, so in some parts of North America it can be more than 30 degrees different than runway alignment. Here's a simple command line to start flying true north at 110 kcas (typical cruise speed for a Warrior or 172) at 5000 ft northbound:

   fgfs --altitude=5000 --heading=0 --vc=110

Often, you will want to start flying in a position relative to an airport, navaid, or intersection. In that case, you can specify the reference position using the normal airport, vor, ndb, or fix options. You then use offset-distance to specify your distance from the starting point (in statute miles, which needs to be fixed), and offset-azimuth to specify the bearing to the reference point (again, in degrees true). This command line starts at 5000 ft 5 statue miles to the east of the Oakland VOR:

   fgfs --altitude=5000 --heading=270 --vc=110 --vor=OAK --offset-distance=5 --offset-azimuth=270

Note that you do not have to be flying towards the reference point: you can pick any heading you want.