DME Range RNAV
DMEDME —Distance Measuring Equipment range is slant range - the total distance from the beacon to the aircraft (including the height difference) and not the plan range (which is just the lateral distance to the overhead.)
For questions on slant range:
- Draw a quick sketch. This helps avoid the obvious error, which is to get the vertical distance of the aircraft above the DMEDME —Distance Measuring Equipment beacon incorrect.
- Look at what units the answers are in — if they are in nautical miles, it is probably better to convert the feet units to nautical miles before doing the calculation. A rough 6000' = 1 nm will suffice for these calculations.
- Use Pythagoras' theorem: .
Two mistakes can be made here:
- Forgetting that you already have the hypotenuse (not the smaller sides) distance and so need to subtract the square of the vertical distance from the square of the slant range.
- Forgetting to take the square root of the answer once you have done the subtraction.
If you get a question on range when directly above the beacon, the plan range is zero, so all you have to do is convert your height above the beacon to nm. Unless you have flown into the beacon, this answer is never zero!
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