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 Cessna C172) 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.

Setting up an approach

To set up an ILS approach realistically, you should start the plane in the air, outside the final approach fix, below the glideslope, on a 30° or 45° intercept. You will normally intercept the localiser first, hold altitude until the glideslope comes down, then reduce power to stay on the glideslope. Here are the steps to set up in the air for the ILS 32 approach into Ottawa (CYOW):

1. Determine the final approach fix (in this case, the Greeley NDB, YRR) and the glidepath crossing altitude (1,800 ft MSL)
2. Determine the magnetic heading for the approach path (320°), then adjust by the magnetic variation (-14°) to get the true heading (306°)
3. choose a starting altitude 500–1,000 ft above the crossing altitude (2,500 ft)
4. choose an appropriate approach speed for your aircraft (90 kt for the Piper Warrior or Cessna 172, though in real life, you might push it to 110 kt at a busy airport)
5. choose an offset azimuth angle from the final approach fix that is 10° greater or lesser than the approach path (316°)
6. choose a true heading that is 30° greater or lesser than the approach path, in the same direction as the azimuth angle (336°)
7. preset your frequencies (110.3 mhz for the ILS 32 localiser; 377 khz for the Greeley NDB)

Resulting command line (using the Warrior II, which launches with the engine running by default):

   fgfs --aircraft=pa28-161 --prop:/controls/engines/engine/throttle=0.7 --ndb=YRR \
        --altitude=2500 --offset-azimuth=316 --heading=336 --nav1=320:110.3 --dme=nav1 --adf=377 --offset-distance=5 --vc=90

Be prepared to make rapid throttle and trim adjustments on startup. Fly straight and level until the LOC needle comes alive, then turn left on intercept; maintain 2,500 ft until the GS needle comes alive, then reduce power to keep it centred. Decision height is 571 ft.