INS Check Points

[cormacshaw]

Hi Ppruners,

Question from a simple simmer looking to aid the developers of the software in question (http://www.x-plane.com) improve the accuracy of the sim's airport infrastructure data model...

Airport parking charts often include a detailed list of the latitude and longitude of INS check points at stands on the airfield. What I'd like to know is to what exact point on the ground and what point on the aircraft do these fairly precise locations refer? My assumption is that it would be the stop line and the nose wheel of the aircraft but I'd like to know for sure. The fact that stands may have multiple stoplines for different aircraft types throws a spanner into my theory for starters.

So if you know for sure, or better still, have a reference to an 'official' source, please reply. Thanks.

[BizJetJock]

I think you're looking for an unrealistic degree of precision here. The positions given are to the nearest 0.1minutes of arc, which equates to an ellipse (unless you're at the equator) of about 180m in Latitude and (180*cosLat)m in Longitude.
Put it another way, when you look at the reams of positions at a large airport you come to notice that several stands are given the same coordinates!

[cormacshaw]

Thanks for the replies so far. Unfortunately the linked document and nothing else I have come across on the CAA, NATS and FAA websites sheds any light on the matter. I'll keep looking and will gladly accept any further pointers.

The coordinates on the UK and Irish charts I have go down to 1/100th of a second which gives precision to less than a metre which is more than good enough for our purposes.

[Fly3]

In our operations we only ever enter the airfield co-ordinates because the navigation system will update to the departure end of the runway in use when T/O power is applied.