T-6A INSTRUMENT NAVIGATION
9. As the aircraft approaches the point, it will be necessary to determine whether you will
reach the radial or the DME first. To come as close as possible to the new point, it will be
necessary to judge the rate at which the DME is moving and the rate at which you are crossing
radials. If determined one rate is moving faster than the other, it may be the aircraft will reach
the DME or radial first rather than simultaneously. Keep the following in mind when trying to
hit a point:
DME Rate of Change. When the bearing pointer is closer to the heading index than
the 90° benchmark, i.e., above the 45° benchmark, the DME will change faster than
the radials. The opposite is true when the bearing pointer is nearer the 90°
benchmark, i.e., when the bearing pointer is below the 45° benchmark.
Remember, unless the winds are very strong, when the head of the bearing
pointer is above the 90° benchmark, the DME will get smaller. When the head
of the bearing pointer is below the 90° benchmark, the DME will probably get
To get your DME to "speed up," turn to place the bearing pointer closer to the
heading index. This will slow the rate at which you are crossing radials. When
going inbound, you will be working with the head of the bearing pointer. When
going outbound, you will be working with the tail.
Radial Rate of Change. To cross radials faster, turn to place the bearing pointer
closer to the 90° benchmark. This will slow the rate of DME change.
You will not necessarily be able to determine the exact heading to roll out on as
you are adjusting heading, but that is not as important as altering your heading
before it is too late. Once on your new heading, let things settle down (cross a
few radials, and let a few tenths of DME pass). Then update again by trying to
determine if you will hit the radial or DME first.
Your goal is to get as close as you can to the desired point. Continually update
until crossing the point.
10. In the event your solution does not work out exactly, you may arrive either at your desired
DME or radial prior to the fix. Regardless of which comes first, you can consider yourself at the
fix once within the distance required by course standards.
1. Failing to expedite the first step. Remember there is plenty of time to refine your solution
once proceeding in the general direction.
2. Failing to make frequent updates. As you get closer to the station, more updates will be
required to ensure an accurate solution.
4-28 INSTRUMENT NAVIGATION