KN 62A showing too low groundspeed in GS/T mode

  • I just noticed a weird behaviour of the KN 62A: I am flying the tutorial flight at 4000 ft and at about 115 kt. When in remote mode and tuned to the SAM VOR, it is showing a plausible ground speed of 124 kts. But if I switch to FREQ mode and tune to the Compton VOR/DME, it is showing a grund speed of only 60 kts in GS/T mode.

    The Garmin GPS also show the ground speed of 124 kts.

    In summary, the KN 62A is showing an implauible low ground speed in FREQ / GS/T mode.

    Edit: The speed dropped further to 06 kts. If I dial in a different VOR, the speed rises in the same mode over 2000 kts for a few seconds and then drops to a plausibel GS in sync with the RMT mode and the GPS 100.

  • DME reported speed is relative to the source. If you are flying directly to or from the navaid, then the speed should be approximately ground speed. If flying tangentially to the navaid, the speed should be 0.

  • This is what the manual for the KN62A has to say on the speed reading:

    The groundspeed feature incorporated in the unit measures the rate of change in DME slant range distance with time. This speed is then read from 0 to 999 knots in 1 not (sic) increments. To obtain accurate groundspeed, the aircraft must be tracking directly to or from the station. To obtain accurate time to station, the aircraft must be tracking directly to the station.

    As a side note, the slant range is the straight line distance from the airplane to the station, rather than the over ground distance. As a naive example, so you can understand the concept: if you are at 6000ft right above the station, the over ground distance is 0nm, but the slant range is about 1nm.

    Also, as another side note, the speed should not read 2000kts. Not only is that higher than what the unit displays, but it sounds like a bug to me.

  • JF Staff

    We're using the default DME speed variable for the KN62 so any potential bugs with that value will need to be reported to Asobo.