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Interesting facts on VFR Aeronautical Charts

Whilst at Airventure last week I sat in on a presentation by John Moore from the National Aeronautical Charting Office (NACO) who talked about some interesting and little known facts about the various VFR charts we use. He showed some statistics about the frequency of changes to the various charts which certainly brought home the logic of flying with current versions. In addition he reviewed some new features on the charts that make life easier and showed an example of how misreading the chart symbols can be costly…

The National Aeronautical Charting Office is the organization responsible for the creation of the sectional charts and other VFR and IFR Charts that many of us use for navigation each time we fly. They are also responsible for many of the core databases and digital charts that crop up in third party navigation products and websites (you can read more about their mission here). We know we should fly with current charts but what really is the difference between the old version and the new version? Here are some general numbers that were presented about the changes made to each type of chart between revisions (info on these and other charts available here):

  • World Aeronautical Charts, new revision every year, average of 493 changes per revision
  • Sectional charts, new revision every 6 months, average of 278 changes per revision
  • Airport and Facilities Directory, new revision every 56 days, average of 775 changes per revision

Between revisions, many of these changes are available via NOTAMs but once they are published on the chart or in the AFD they are no longer included in NOTAMs and so without the up to date chart/AFD you would never know about the new tower or the change in CTAF frequency. Mr Moore went to great lengths to stress the need to fly with current charts and other documents. IFR pilots are very aware of this and almost always have some type of subscription to ensure they are always flying with current approach plates and en route charts. The same subscription services are available for VFR charts and as Mr Moore said “If you don’t get a subscription from us, get one from somewhere!”.

He discussed the process for requesting new features to be added to the charts, saying that many requests get made at events like Airventure and that new requests follow a procedure for being reviewed and evaluated prior to implementation. A new feature that has appeared recently are parachute jump frequencies that are listed next to known jump sites so pilots can monitor the frequency used by the jump plane pilots and jumpers to know when they might expect to be surrounded by multicolored parachutists.
Com frequency for parachute jump sites

New VFR GPS waypoints are being introduced for pilots to use in VFR flights. These will be present in the GPS database and are not meant to be entered manually. On the chart they are shown using the waypoint symbol and have five letter identifiers beginning with VP— (older ones began with VV). They may or may not be collocated with VFR Checkpoints (the magenta flags), in which case the five letter identifier is shown under the checkpoint name.

Chart representation of VFR waypoints

Mr Moore made a potentially life-saving point when describing the chart representation of mountain passes. The chart symbol shows the entrance to a mountain pass and list the altitude of the pass (see figure below).

The altitude listed is that of ground level, the height your GPS might read if you were standing at that point. It is not a safe height to fly through the pass! Similarly, the ‘channel’ shown by the chart symbol merely shows the entrance to the pass and does not represent a safe course through the entire pass. He showed an example near Snoqualmie, WA where the pass takes a 90˚ turn halfway through (See chart excerpt below, imagine you are approaching the pass from the SE and follow the bend in the road), something you would miss if you didn’t check the chart closely and sadly, something that an unfortunate pilot found out to his cost.

Snoqualmie Pass
He discussed other interesting points about information represented on the charts, much of which can be found in the online version of the Aeronautical Chart User’s Guide (the screen shots above were taken from the guide). It is also available in printed form with a new version scheduled for early 2006. NACO offers a wide variety of information on their website so its well worth checking out. You can view and download current instrument approach procedures and airport diagrams (they provide current and pending versions so make sure you get the version that will be current for the day you plan to fly) and subscribe to charts in both paper and digital form.

All in all it was a very useful presentation and I also learned about the features on their website which will also prove to be very handy.

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