VOR/DME holding 2

07.09.2011

Submission:

The rationale for that bit is as follows: when you have an tolerance error on the DME it will be in the same direction when starting the outbound turn and when ending it. It is not possible that the system performs in one direction in a moment and 2 minutes later it performs in the other direction. So that calculation was to reduce the DME error only to the sum of the distance related component. However, it still refers to the old DME tolerance from the early nineties of 0.5NM (plus 1.25% of d). So it takes both DME tolerances together and deducts the fixed value of 2 times 0.5NM. But as the DME tolerance has changed to 0.25NM, it will produce a negative number, which makes no sense at all. My view: forget that operation as it does not make a big difference, just apply the spiral curve from C'3 down along the arc and you are fine.

Beat Zimmermann - Air Navigation Institute GmbH - Switzerland