Originally Posted by Underfire
mansfield, I think you need to read up a bit on RNP and the parameters.
YOU need to read. Mansfield is correct. I suggest you read up on "Flight Technical Error", Underfire.
the aircraft will fly as accurately as it can, which most of the time is to around 0.02nm accuracy (which is known as ANP or Actual Navigation Performance).
No; read what Mansfield said. "As accurately as it can" is FTE. The ANP can be 0.02, but the aeroplane can be off track for a number of reasons, including hand-flying Bloggs making a hash of his RNP approach when the AP is out of action.