Update

STUDENT GUIDE

VISUAL NAVIGATION

7.9.2.3. Update is a critical part of the navigation process. As the example above shows,

failure to update times enroute when no correction is made leads to faulty wind

computations. Failure to update can also cause missed checkpoints and turns.

7.10. UPDATE

7.10.1. The previous example is just one reason why updating check points and turn points is

critical. Many of the intermediate turn points and check points may be smaller features with

limited vertical development, and at 500 feet AGL and 300 knots ground speed these features

may be visible for only a short time-- as little as 12 seconds. Due to this short opportunity for

visual acquisition, it is critical the crew looks in the right place at exactly the right time.

Remember even minor updates of only six seconds translate to a half mile.

7.10.2. Updating is not just a term applied to maintaining timing to points. This term also

applies to the process where corrections (course or timing) are modified after initiation. For

example, two minutes into a three-minute timing correction an intermediate check point indicates

the aircraft is only three seconds off preflight timing. The proper reaction in this scenario is to

terminate the correction in thirty seconds (2+30) rather than letting the correction run the original

allotted time (3+00). Likewise, if a course correction for 1 NM is initiated (10 for 1+30), but

after 45 seconds an intermediate checkpoint indicates the aircraft is only NM off course, the

prudent choice is to terminate the correction after 1+15 (30 seconds).

7.10.3. Another situation requiring "Update" techniques occurs when the aircraft turns abeam a

turn point rather than over it. In this scenario, the distance left or right of course may translate

into timing errors. Likewise, if the aircraft must turn early due to weather or turns late due to

aircrew error, this induces track error on the following leg. The resulting errors are described

below in Figure 7-7.

7-13