NavList:

Howard G
Forgive me if I don't C&P your very informative post below.  

I would agree with your 10nm for an airborne celestial fix.  During the RAF Bomber/Strike Command Bombing and Navigation Competitions of the 60s, and 70s, the best crews from each RAF Vulcan and Victor Squadron and a detachment of SAC B52s switched radar, doppler, and RDF off and flew out into the Atlantic at FL430, M0.84 for a couple of hours and returned at FL410 to the desired destination, which was scored by a Radar Bomb Score Unit (RBSU).  You also switched the radar on 5nm before e.t.a. so the PPI picture could be scored if you were so far off that the RBS failed to pick you up.  Scores ranged from a lucky mile or two to well over 10nm.  The median score must have been somewhere between 7 and 10 nm.  I can’t remember exactly.  On the bombing sortie, you completed two simulated bombing attacks from FL410 or 430 and two low level attacks from 500’.  In 1973, our crew won the bombing, but as far as I can remember our celestial score was about 11nm.  All aircraft caried an umpire, which is how I managed to get a couple of B52 trips in my logbook.  SAC was also invited to place a B52 Colonel and Captain with our scoring team; so close was the competition between SAC and the RAF. 

You’ll note I placed the caveat ‘initially’ in my sentence about finding Howland Is.  I assumed that when they didn’t find it first go, they would have gone into some sort of a search pattern.  Hence the 337/157 call.  Noonan might have aimed off, but that is less likely than Chichester deliberately doing so, because they were expecting to finish with radio and smoke assistance from Itasca.

I think the lack of vertical extent of Howland (10ft + the height of any buildings) Is was significant.  As well as being somewhat bigger, Norfolk Is and Lord How Is in Chichester’s case extended vertically to 1047’ and 2871’ DaveP