AFI 11-2C-130v3 - BITS

AFI11-2C-130V3 23 APRIL 2012 157
11.14.3.2. When taking heading checks at high latitudes, it is advisable to place data into
the periscopic sextant to give the true heading and convert this heading to grid by
applying the assumed LONG/CA.
11.14.4. Construction and use of the ZN graph is optional. The ZN graph is based upon the
route of flight and dead reckoning. See AFPAM 11-216 for construction procedures.
11.14.5. Departure Requirements:
11.14.5.1. Polar true/grid courses as reflected in FLIP terminal charts will be used for
departures in polar areas. Before takeoff, visually align the aircraft with the runway
heading and set the polar true/grid course of the runway in the aircraft's directional gyros.
The navigator will set applicable systems in gyro mode with the correct latitude set.
11.14.5.2. After reaching flight altitude, determine the polar true grid heading and reset
the primary and secondary gyros. The type of chart being used will determine whether
the heading will be polar grid heading or convergence grid heading.
11.14.6. Enroute Requirements:
11.14.6.1. The Grid Entry/Exit section of the AF Form 4116 will be completed prior to
heading reference changes. When entering grid operation, spot grivation should be
applied to the computed magnetic heading to obtain DGH. The aircraft will be
established on the computed magnetic heading prior to resetting the heading references.
When exiting grid, the computed magnetic headings will be the target heading when the
compass systems are reset. In both cases, the computed magnetic headings will be
compared to the flight plan to verify the accuracy of the courses measured and conversion
data used. This will ensure the validity of initial entry headings and provide precise target
headings for exit.
11.14.6.2. Normally, the grid heading will be checked each 30-minutes after grid entry.
If the compasses are precessing 3 degrees per hour or less, hourly checks may be
obtained after the first hour. NOTE: On aircraft with reliable SCNS/INS, if the
SCNS/INS heading is within 2 degrees of the initial celestial-derived grid heading, the
SCNS/INS may be used to determine gyro precession.
11.14.6.3. Determine the precession information for each gyro after each heading check.
When a gyro‘s precession is greater than 1 degree, reset the gyro to correct grid heading.
When the period precession is 1 degree or less, the navigator may either reset the gyro or
treat the precession as zero.
11.14.6.4. Whenever the period precession is greater that 1 degree (optional for 1 degree
or less), the hourly precession rate may be removed by use of a false latitude setting.
When the combined earth rate and gyro precession are less than +15 degrees/hour, the
false latitude setting will totally compensate for precession. Two considerations are
necessary:
11.14.6.4.1. Predicted precession becomes zero.
11.14.6.4.2. It may be necessary to adjust previous DR and air plot positions if the
precession rate changes at subsequent heading checks. If this occurs, adjustments
normally will be small and have negligible effect on DR and air plot accuracy;
however, the effect should be considered.