18.104.22.168. 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.
7.10.1. 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 1½ NM is initiated (10° for 1+30), but
after 45 seconds an intermediate checkpoint indicates the aircraft is only ½ 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.