Ref Posts 4272 & 4278
Dougie an old photo of you in pre- Omega days. You look wonderfully in control.
Reference your comments about straying off track in N.Atlantic and being violated. I can recall only two extreme tracking errors. One a VC10 and the other a C130. IIRC the VC10 navigator was flying with the compasses set to Directional Gyro(DG) and had a South Latitude (instead of North) selected on the Earth Rate Drum. The Herk nav used Variation instead of Grivation to correct the navigation computers. These mistakes introduced large heading errors. Luckily, both were westbound and the errors turned the a/c north towards Greenland. I believe the errors became apparent when a very large CB in the shape of Greenland was seen on the CCWRs.
Track keeping on the C130 in my day (until 1995) was a lot easier when the magnetic compass was switched to Gyro (DG) and gyro/grid technique was flown. The accuracy of the magnetic compass, although swung accurately to .1degree, depended largely on the accuracy of the magnetic variation and how adept you were in keeping the local variation updated as you stooged along. The variation lines plotted on the charts are a mean and change position slowly with time as does the position of magnetic north. Local variation can also be radically different from that printed on the chart. In the DG mode there is no magnetic influence on the compasses and hence no magnetic error.
The introduction of Omega and its digital computer, allowed the Azimuth of the Sun, (or other heavenly bodies) to be computed in degrees True to within an accuracy of .1 degrees. The a/c heading , using the periscopic sextant, aligned on the bodies azimuth, could be read to about the same accuracy. With the appropriate corrections to convert this to a Grid heading, this reading would be compared to the C12 DG readout. Any wander of the gyro from the correct reading would be removed and a gyro wander rate established which would then be tuned out, hopefully to zero by altering the C12 latitude drum (Earth Rate). It was possible, during the flight, to get the DG wander rate less than 1 degree/hour.
Astro shots were also made more accurate in DG mode because there was no ‘hunting’ of the C12 as it annunciated to refine the magnetic heading. (This reduced heading acceleration error. For example a turn of .5degrees at 300kts would give an astro error of 8nm) It was normal practice to go to DG, when not flying gyro, whilst shooting astro to alleviate this error.
The Doppler drift and G/S, I believe were quite accurate, disregarding surface motion of the waves, as was the Along/Across (AA) track computer. The A/A computer could be fine tuned trackwise by setting a false track to compensate for the track error You could not do anything to the Distance to Go counters to make them more accurate but then the most important thing was correct tracking. The Latitude/Longitude computer was a disaster and could rarely be trusted, it spent most of its time running away in any direction at about 1000kts!
Before the introduction of Omega the azimuths of Stars/Planets had to be laboriously extracted from the Sight Reduction Tables or from graphs where it was difficult to get the required accuracy and you very often used to introduce errors into an otherwise accurate gyro. It was very laborious and I only did it when strictly necessary
(The alignment of the sextant on the a/c centreline was always checked before a major navigational routes by checking that the fin of the a/c was in the right place!!!: 180.4 degrees if I remember correctly).