RF ARCS

[PT6A]

Ok something I started to play with the other day in google earth...

I was plotting in some RNP tracks, I have the start and end fix of the ARC, the direction of the ARC and the distance of the ARC...

Now how do I calculate the ARC center?


Any ideas?

PT6A

[punk666]

I have the start and end fix of the ARC, the direction of the ARC and the distance of the ARC...

The dme distance is not he length of the arc but the distance from the centre point. Usually a VOR is centre point.

[aterpster]

PT6A:

First issue that has to be determined is what the radius of the RF leg needs to be. The FAA 8260.52 has wind tables and TIAS assumptions for that.

Then, where an RF leg joins a TF leg it has to be at the tangent of the TF leg.

The arc center point is simply the "hub" of the RF "wheel." The arc center point has to be included in the database in order for the avionics to be able to calculate the RF leg.

An RF leg can also join another RF leg of a different radius or direction but the rule of tangents must still be observed.

[aterpster]

punk666:

DME arcs are specified as an AF leg by ARINC, as opposed to an RF leg, which is an RNAV leg type.

AF legs have to be specified so that RNAV avionics can fly a DME ARC using RNAV.