I know that the various NAT tracks are of different lengths because of the latitude they are at: But what is a good figure for this distance (KBOS-EGLL)? (I assume that KBOS is the closest US airport to EGLL on the great circle?). Maybe a typical ETOPS and non-ETOPS distance would be great.Thanks,Bruce.

Bruce,Go to this link (Great Circle Mapper)http://gc.kls2.comfollow the instructions. It is pretty basic. Enter the ICAO or IATA ident for the departure and arrival (and enroute airports if you want). It will give you the GC distance and time (you enter the average Ground Speed). Most routes are within 5% of the GC distance.Kevin in CYOW

Thanks Kevin.

Great link- I've just gotten home and tried it.Thanks again,Bruce.

You're welcome. Happy to help.Kevin in CYOW