Figure 12 - P-8010047

INSTRUMENT NAVIGATION

Here is a simplified account of a flight from Semmes to Crestview:

1. Tune and identify the Semmes VORTAC.

2. Fly on its outbound radial for half the distance of the jet route segment.

NOTE: In this case the radial and the course are both 081 magnetic.

3. At the halfway point (43.5 DME), tune and identify the Crestview VORTAC.

4. Fly inbound on the 263 radial of the Crestview VORTAC.

NOTE: In this case the radial is 263 and the inbound course is the reciprocal, or 083.

It should be mentioned that while the chart (Figure 11) shows the J-2 route as a straight line,

the course actually differs by 2. This is caused, in part, by a change in the Earth's magnetic

variation between the navaids.

Continuing east from Crestview towards Tallahassee on J-2, you will notice that the airway is

NOT a straight line. It has a "Dog Leg" 80 (28+52=80) miles east of Crestview. (Figure 12)

Figure 12

The procedures for flying this leg of J-2 are basically the same as the Semmes to Crestview

leg. In this case the position at which you change navaids differs from the "halfway" rule.

When flying J-2 from Crestview to Tallahassee, change navaids at the mileage breakdown point

depicted on the chart. Your inbound flight to Tallahassee would be on the 288 radial (Course =

108).

Another exception to the rule of changing navaids halfway along your route of flight occurs

when you encounter a "changeover point". Figure 13 depicts J-118 between Memphis and

Chattanooga. If you were flying easterly along J-118 you would not switch your navaid at half

the distance (238/2=119). You would switch it at the changeover point (130 DME).

RADIAL TRACKING AND COURSE CONTROL 3-9