FAA FAR 77 tool warning: “Airport reference point and runway end points are significantly different” with validated geometry

CarieErnst_KYTC

Hello,

I am running the FAA FAR 77 tool in ArcGIS Pro (version 3.5) and consistently receive the warning:

“The airport reference point and the runway end points are significantly different. This may cause the obstruction identification surfaces to generate incorrectly.”

However, I have validated the geometry and cannot identify any spatial inconsistency:

• Single runway airport

• Runway length: 3849.97 ft

• ARP to Runway End A: 1924.70 ft

• ARP to Runway End B: 1925.27 ft

• Difference from midpoint: ~0.57 ft

• Data projected to WKID 3089 (Kentucky Single Zone, US Feet) Vertical WKID 6360

• Map coordinate system matches dataset

• No displaced thresholds

• Only one runway feature

• Runway centerline is a simple 2-vertex line

• Airport elevation parameter correctly supplied (1040 ft)

• Runway end elevations are consistent

• No joins or definition queries

• All features exported into a clean file geodatabase

The generated OIS surfaces appear correct and centered.

Given the above, I am trying to determine:

1. What tolerance threshold triggers this warning?

2. Is the check purely horizontal, or does it include vertical comparison?

3. Is this known to occur due to internal reprojection or rounding?

4. Can this warning safely be ignored when geometry is validated?

Any insight into the internal validation logic would be appreciated.

Thank you.

Sara_Courter

Hello @CarieErnst_KYTC 

 

I have already responded to your email, but I wanted to post this answer for the community to see.  

 

I have read through your parameters, and below is a response to your questions. 

 

1. What tolerance threshold triggers this warning?
   The tolerance is 150ft. The reason the tolerance is 150ft is that if the horizontal surface is too high or too low, it will not intersect the approach surface and hence fail to generate transitional surfaces. However, I see this warning all the time when I run the tool with the COS data. However, I do see there is a 900ft difference between your ARP and the Runway Ends, is this correct?
2. Is the check purely horizontal, or does it include vertical comparison?
   It's mostly focusing on the Horizontal and Conical surfaces. The primary, approach, and transitional are based on the elevation of the runway ends.
3. Is this known to occur due to internal reprojection or rounding?
   No, as stated above, this is just so the user is aware and has the opportunity to double-check the geometry. 
4. Can this warning safely be ignored when geometry is validated?
   Yes, if you have checked your geometry of the multipatches and everything looks good, you can safely ignore the message. 

Additionally, we have made enhancements to the FAR 77 tool. If you haven't already, please feel free to check out this brief tutorial on Creating Part-77 Surfaces.

 

Best,

Sara