7.26. Fix-to-fix. Proceed directly to a point defined by radial/DME, and/or RNAV waypoint using onboard navigational equipment.

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7.26.1. Objective. Proceed directly to a point defined by radial and DME, using onboard navigational equipment.

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7.26.2. Description. Specific points on the EHSI represent location and target radial or DME. The relative positions of current and desired position enable determination of the course between them.

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7.26.3. Technique.

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7.26.3.1. Tune, identify, monitor (TIM) NAVAID and confirm the correct frequency is selected. Set radial of the desired fix in the CSW.

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7.26.3.2. Turn in the shorter direction to a heading between the head of the bearing pointer and the head of the course arrow (which is the desired radial). Favor the head of the bearing pointer (which brings you closer to the selected station) if destination DME is less than current DME. Favor the head of the course arrow if destination DME is greater than current DME. Note: A heading (in a no-wind condition) exactly between the head of the bearing pointer and the head of the course arrow results in arrival at the target radial at the same DME as current DME. If both the bearing pointer and the head of the course arrow are in the upper half of the EHSI, the DME will initially get smaller than the current position DME before increasing to the target DME (referred to as “cutting the arc”).

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7.26.3.3. After turning to an initial heading, fine tune and update the fix-to-fix by envisioning the aircraft’s current position and the targeted fix superimposed on the EHSI as if it were a map. Use the DME of the position (current aircraft location or desired fix) furthest from the station as the distance to the outer ring of the EHSI bezel. The ground station is then located at the center of the EHSI. The current aircraft position is always somewhere on the tail of the bearing pointer, and the targeted fix is always somewhere between the center and the head of the course arrow. The relationship between the two points allows determination of turn direction and an estimate of the initial heading. Figure 7.3 and Figure 7.4 depict a fix-to-fix heading computation from the current aircraft position (180 radial at 60 DME, heading 360 degrees) to the targeted fix (090 radial at 30 DME). Current position is 60 NM south of the station, heading north. The target fix is 30 NM east of the station. The resultant heading to the fix under no wind conditions is approximately 025 degrees.

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7.26.3.4. The following simple facts can prevent confusion. Current aircraft position is always somewhere between the tail of the bearing pointer and the center of the EHSI. The target fix is always somewhere between the center of the EHSI and the course arrow. The distance from the center to the outer edge of the compass card is always equal to the larger DME; therefore, either the current position or target fix is located on the outer edge of the compass card.

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7.26.3.5. The pencil method may be used to determine heading from current position and target fix. A pencil can be used (or just visualize straight line) to connect the two positions with an imaginary line (Figure 7.3, photo C). Then imagine a parallel line through the center of the compass card. This line through the center of the compass card intercepts the no-wind heading to the target fix (Figure 7.3, photo D). A pencil is not necessary but may help develop the ability to imagine the proper lines.

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7.26.3.6. The “plumb bob”/vertical string visualization can supplement the pencil method to determine heading to the target fix. As in the pencil method, imagine a line between current position and target fix. Turn to put the line in a vertical orientation (fixes aligned vertically).

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7.26.3.7. Apply known wind drift corrections. A requirement for significant heading changes during updates can indicate approximate windspeed and direction. Proper wind drift correction can be determined by dividing the crosswind component by the true airspeed in NM/minute min. For example, if the no-wind heading is 360 degrees, the crosswind component is 30 knots out of the west, and the airspeed is 3 NM/minute (180 NM/hour divided by 60 sec/minute = 3 NM/minute), the drift correction is 10 into the wind (30 divided by 3 = 10 degrees) for a resulting heading of 350 degrees to proceed toward the fix.

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7.26.3.8. Regularly update the required heading to the target fix. Simply repeat the steps used to determine the initial heading (always use current DME). It can be helpful to schedule updates at distances that form simple ratios with the target DME. For example, if going from 60 DME to 15 DME, plan updates at 45 DME (1:3 ratio), 30 DME (1:2 ratio), and 20 DME (3:4 ratio). Mathematical ratio methods may also be used to determine heading. A heading midway between the bearing pointer and course arrow results in hitting target radial at DME same as current DME. A heading midway between the midpoint and course arrow results in hitting target radial at DME twice the current DME. Likewise, heading midway between the midpoint and the bearing pointer results in hitting target radial at DME one-half the current DME.

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