the 12 minute mark. Because it falls outside the turnpoint circle, annotate it with the standard
three minute interval tick mark.
3. Continue measuring back for the 11, 10, 9, etc. minute marks. In this manner, errors due to
measurement are less likely to affect your timing in flight.
Figure 2-6 Drawing Time Ticks
UPDATE CHART FOR TOWERS AND OBSTRUCTIONS
Generally, the National Imagery and Mapping Agency (NIMA) produces new editions of TPC
charts only every five years. However, details on a typical H-24B change much more frequently!
To account for this, NIMA produces a Chart Updating Manual (CHUM) that specifies the most
current edition of a given chart as well as any changes or discrepancies on the chart. The CHUM
is published on a semi-annual basis, with supplements produced each month (Figure 2-7).
Therefore, to update a given chart, use both the monthly supplement as well as the semi-annual
CHUM. Additional chart changes may be listed in Flight Information Publications (FLIP) such
as AP-1B, or in NOTAMs.
LOW-LEVEL CHART PREPARATION