AFI 11-2C-130v3 - BITS

158 AFI11-2C-130V3 23 APRIL 2012
11.14.6.5. To determine false latitude correction, enter the earth rate table with the
desired latitude and extract the tabulated earth rate value. Algebraically combine the earth
rate value and the observed hourly precession rate (use cumulative precession rate once a
false latitude has been set). Re-enter the earth rate table with the combined value and
extract the corresponding false latitude.
11.14.6.6. Only 15 degrees/hour can be removed by a false latitude setting. When the
sum of earth and primary gyro precession rates exceeds +15 degrees, the navigator must
artificially steer the aircraft (in effect, the aircraft will fly a gentle arc) to compensate for
the amount of precession in excess of +15 degrees/hour. The formula used to correct the
DGH to an initial grid heading (IGH) to fly appears on the AF Form 4116 as "RT/2
CORR" (note that the formula produces a correction, so the precession rate must be given
its opposite sign). The precession rate used in the formula must be adjusted to reflect the
time period in the DR ahead. When "carrying" precession as suggested above, the
navigator should consider several aspects of the navigational problem. NOTE: When
precession exceeds 15 degrees per hour, consider the compasses unusable.
11.14.6.6.1. If alter headings are not made at heading check times, precession will
have accumulated by alter heading times and a correction (opposite sign of
precession) should be applied to the IGH using the total precession correction portion
of the AF Form 4116.
11.14.6.6.2. If the precession rate changes at subsequent heading checks, it may be
advisable to adjust previous DR and air plot positions described at paragraph
11.5.7.6.
11.14.7. Miscellaneous Procedures:
11.14.7.1. Normally, when changing charts or crossing the 180 degree meridian, only the
reference changes; the heading of the aircraft is not altered. The change is made by
comparing the grid courses and applying the difference to the gyro reading (old chart GC
350 degrees; new chart GC 331 degrees; GR 353; 350 - 331 = 019 = 334; reset the gyro
to read 334).
11.14.7.2. Do not use the combined rhumb line/coriolis correction when flying DG. Use
only coriolis correction for celestial observations.
11.14.7.3. Always recheck computations and formulas when a radical change in
precession is observed.
11.14.7.4. Grid qualified navigators will maintain proficiency in grid procedures.