If the RMI (Radio Magnetic Indicator) heading rose gets stuck, would the RMI needle still display correct QDM (magnetic bearing to station)?

  • $\begingroup$ Define what you mean by “correct”? How would you read the needle? Is the question “Does it display correctly” or “Can the correct information still be derived?” $\endgroup$
    – Jim
    Dec 6, 2021 at 15:09
  • $\begingroup$ @Jim: can the correct information about QDM be derived? $\endgroup$ Dec 6, 2021 at 15:24
  • 1
    $\begingroup$ @SachinChaudhary Please always edit your question to include all information when asked for clarification. People shouldn't have to read through the comments to understand the question. $\endgroup$
    – Bianfable
    Dec 6, 2021 at 15:37

1 Answer 1


It would be like a "Fixed Card" ADF (old style indicator).

If your actual magnetic heading was 040 degrees but the heading rose was stuck indicating a magnetic heading of 280 degrees and the RMI needle was pointing at 330 degrees on the heading rose, then the "relative" (correct) bearing to the station would be 50 degrees to the right.

So, with a bit of arithmetic (actual magnetic heading of 40 degrees + relatve bearing to the station of 50 degrees) the derived magnetic bearing to the station would be 90 degrees.

RMIs typically have 2 bearing pointers (for example, one for ADF and one for VOR) but the "relative" bearing principle would be the same.

  • $\begingroup$ But the QDM information is already contained in the VOR signal, so the receiver actually knows the value of "QDM" when the signals are received. So wouldn't the RMI nose simply point to that known QDM value? Since it's pre known from the VOR signal. $\endgroup$ Dec 6, 2021 at 19:31
  • $\begingroup$ @SachinChaudhary I don't think so. The RMI needle would simply point to the VOR station (just like pointing to an NDB). If the Dictional Gyro (DG) was stuck the needle would just rotate until it was pointing to the VOR. Similar with respect to an HSI (earlier question) the RMI is two separate nav components in the same container. They are not making integrated and coordinated calculations just combing two separate overlaying functions in the same display. (Although, other functions like using a heading bug to command the autopilot, etc. is possible). The RMI is not that sophisticated. $\endgroup$
    – user22445
    Dec 6, 2021 at 19:43

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .