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The One to Sixty Rule

One to Sixty The One to Sixty Rule has many practical applications in air navigation. The proper use of this rule enables the pilot to accurately calculate various navigational problems such as:

    Wind corrections
    Time and Distance calculations
    Slope calculations
The theory of the One to Sixty Rule is based on the fact that a ONE degree arc on the Equator equals approximately 60 Nautical Miles (See Earth's Coordinate System) or in other words a ONE minute arc equals approximately 1 Nautical Mile. Solving navigational problems with the One to Sixty Rule is fairly simple. When a deviation, in distance, is known and the distance from an original point is also known, the following proportion holds:

Proportional

DRIFT CORRECTION

In the following example, an airplane drifted 8 NM after flying 65 NM. Three steps are required to find the wind correction angle needed to arrive at the destination.

    Example
    Step 1 - The drift in degrees
    Solve triangle CAD
    8/65=ANGLE/60 or ANGLE=480/65=7.3 Degrees
    Step 2 - Correction in degrees to destination
    Remaining distance AB - AC = 100-65=35
    Solve triangle CBD
    8/35=ANGLE/60 or ANGLE=480/35=13.7Degrees
    Step 3
    Add angle CAD to angle CBD to find heading to fly
    7.3+13.7=21 degrees

DISTANCE AND TIME

The formulas for determining time and distance to a station are also derived from the One to Sixty Rule. The distance to a station can be calculated by flying an aircraft perpendicular to a given bearing (or radial) and by noting the elapsed time between bearings. For reasons of convenience, increments of 10 degrees changes in bearings are desired. The One to Sixty proportion is the basis for obtaining the desired formula.

The relationship in (a) is similar to the one shown earlier.

formula

The distance between bearings is a function of the aircraft's speed and the lapsed time. Using basic Algebra leads to the following conclusion (b):

formula
    or
formula

Combining (a) and (b) results in the following formula:

formula

Similarly, the time to the station can be calculated using the One to Sixty Rule. The following proportion is derived from the One to Sixty Rule:

formula
    or
formula

To determine the time/distance to a station these steps are to be followed. After tuning and identifying the VOR station:

  1. Determine the radial on which you are located.
  2. Turn inbound and re-center the needle if necessary.
  3. Turn 80 right, or left, of the inbound course, rotating the OBS to the nearest 10 increment opposite the direction of turn.
  4. Maintain heading. When the CDI centers, note the time.
  5. Maintaining the same heading, rotate the OBS 10 in the same direction as in step 3, above.
  6. Note the elapsed time when the CDI again centers.
  7. Use the formulas shown earlier to determine the Time/distance from the station.
A similar procedure can be used to calculate Time/distance from a NDB station.

SLOPES

Another practical application of the One to Sixty Rule is estimating the height of a cloud by using the RADAR echoes return. The RADAR antenna is tilted up and down to points where there is no return.
The distance of the cell is given by the RANGE ARCS and the Tilt Angle is derived from the difference between the lowest and the highest echoes.

formula

From the One to Sixty Rule-

formula

It follows that the height of the cloud in Nautical Miles-

formula

The height of the cloud in Feet-

formula
OR
formula

The following approximation is widely used as a rule of thumb -

formula



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Last update May 17, 2005
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