Originally Posted by
TeeS
Hi again applecrumble
In the attached screenshot, I have overlaid the fix tolerance areas and protection areas for an LNAV approach on runway 27 at EGBJ in the UK.
The fix tolerance area at the Intermediate Approach Fix (NIRMO) is RNP 1 so is 1nm on each side of the fix and 0.8nm before and after. The complete rectangle of the fix tolerance area is included in the obstacle assessment of the protection areas of the intermediate segment (shown in black).
The fix tolerance area at the Final Approach Fix has reduced to RNP 0.3 so 0.3nm each side of the fix and 0.24nm before and after. The complete area shown in orange is assessed for the required minimum obstacle clearance (246ft in the final approach segment) so even if you descend at the earliest fix tolerance then you are still protected.
Hope that helps.
TeeS
.
Thank you so much for such a great answer. Just to make sure I’ve understood correctly, the area within the black “funnel” is the area used to asses obstacles and terrain. Then the fix tolerance 1X or 0.8X rectangle is used to determine worst case for tracking and descent with regards to terrain and obstacles.