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Thread: NAV radios and Course

  1. Default NAV radios and Course

    So I haven't flown the big jets for a while (737-400 for FS9) but have just started to again since I put together my home cockpit. I use a Seitek radio panel and multi-panel (for auto pilot). I plugged in a flightplan for CYYZ-KBNA and took off and everything seems to be ok. I am wondering if the following is normal or if there is a problem with my equipment:

    Flying along heading toward VOR XYZ at freq. 122.5 tuned on my NAV 1 radio (i just made this number up as I don't have the flight plan with me at the moment) My next waypoint is VOR ABC at 125.5 so I set this into NAV 2 and when the time comes to track toward the new VOR I switch 125.5 to the active radio...and the NAV button on the auto pilot is on and the GPS/NAV toggle switch is set on NAV by the way) After tuning the new frequency the plane doesn't turn. To get the plane to turn I had to set the COURSE on the auto pilot to a number which brought the lines on the HSI into alignment. When I did this the plane started tracking the new, just wondering if this is how it supposed to go. If so, then I guess the NAV radio tells you where the VOR is while the COURSE setting takes you there? I used to be big into the flight sim and flew many hours online years ago but I thought that when I flew back then, setting the nav frequency into NAV 1 radio is all that I had to do and the plane would change its course...guess I'm wrong....or there is something wrong with my equipment?

    Thanks for your help!!

  2. #2
    Join Date
    Mar 2005
    Hawaii - PHHI


    When you tune your nav radio to a VOR, the radio receives two signals from the VOR (assuming it is in-range, use the audio to listen to Morse code to confirm). To make use of those two signals, they must be combined. This is done in the VOR indicator or HSI. When the signals are combined the "course" or "OBS" knob/setting is used as part of the "combining". The result is shown on the indicator or HSI as a moving needle and to/from pointer. The same result is sent to the autopilot (when the nav/gps switch is in nav position). In general the autopilot is not a "homing" device. Instead it attempts to align the aircraft with a specific radial of the VOR determined by the course/OBS setting. Depending on the sophistication of the autopilot, it needs to have the aircraft placed on a heading that will intercept the commanded radial manually. If you are intending to fly direct from VOR to VOR, after changing the frequency you need to set the radial to the next VOR from your flightplan or a chart. Note that most VORs use magnetic radials, but aren't necessarily exactly the same as the current magnetic variation, so the radial as obtained from the chart may not be exactly the same as the actual course.

    scott s.

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