Common Scales and Usage

CHAPTER ONE

T-6A NAVIGATION

COMMON SCALES AND USAGE

The information contained on a chart is a function of the chart's scale. The scale is the ratio

between the dimensions of the chart and actual dimensions represented. Thus, if the scale is

1:1,000,000, one inch of the chart represents 1,000,000 inches (about 14 miles) on the ground. If

the scale is 1:500,000, one inch of the chart represents 500,000 inches (about 7 miles) on the

ground. Note a scale 1:500,000 is larger than 1:1,000,000 (a large scale chart gives you a large

amount of detail and a small amount of area).

The choice of scale for an aeronautical chart depends on two factors:

The size of the area to be charted.

The amount of detail to be shown, as limited by the probable use of the landmarks in

navigation.

The conflict between chart requirements for local and long distance flights has led to the

development of numerous special purpose charts at different scales. The objective is to put as

much information on the chart as possible without cluttering the chart to the degree it is less

useful. The scale of charts used in general long range planning is typically between 1:5,000,000

to 1:1,000,000. For detailed area planning, a scale of 1:500,000 to 1:25,000 is effective. This

coverage is too small for convenient use in aircraft which rapidly "fly off" the chart or fly sorties

of extended range. This necessitates frequent transfers to adjacent charts and subjects the

NFO/WSO/NAV to the difficulty and confusion of continuously paging through chart sheets and

pages during flight.

Some chart types and scales:

Global Navigation Chart (GNC), scale 1:5,000,000 (small scale)

Jet Navigation Chart (JNC), Scale 1:2,000,000

Operational Navigation Chart (ONC), scale 1:1,000,000.

Tactical Pilotage Chart (TPC), scale 1:500,000 (large scale).

Chart usage:

GNC and JNC: Used for long range preflight planning.

ONC: Used for medium range preflight planning or used in the air by medium to high

altitude aircraft.

TPC: Used for detailed planning and in-flight use by low to medium altitude aircraft.

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CHART LEGEND REVIEW