Greybeard
It looks like I may have solved the problem. So far I have only changed Salamaua airfield but the aircraft can spawn perfectly on the runway and not in the water.
I am working away from home at the moment and do not have access to my gaming PC so this is taking longer than it normally would.
Hello Greybeard
Not good news I'm afraid!
Despite spending many hours over the weekend on the NGNB maps, I am unable to resolve the takeoff spawn problems.
Only on Salamaua was a partial fix possible - simply by moving the Runway Arrow to its furthest extent on the airfield (to just before the seaward coastline) - this allowed one flight to spawn completely on the runway
On all the other runways including Gusap the spawn points were unchangeable, no matter how all the components were manipulated.
Mubo Airfield also lacks sufficient level ground for a working runway to be feasible - to fix this would require modification to mapH.
It seems the map designers did not fully test all the airfields before releasing the map - there may also be invisible plates that are affecting the geometry of the runways and spawn points.
I am of the opinion that the only solution would be to rebuild the affected airfields from scratch!