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Plotting (New School)


Those of us who grew up with celestial charts and perhaps a palletized inertial navigation system knew the world had forever changed with the introduction of the Global Positioning Satellite system. But still we clinged to our plotting charts, dividers, and plotters. Well it has happened again. This from the FAA in 2016:

[AC 91-70B, ¶] Up to now the only recommended method of cross-checking aircraft position in the oceanic airspace environment was manual plotting on a chart. However, a panel of aviation industry and FAA personnel completed an Operational Safety Assessment of methods for cross-checking oceanic flight navigation. The panel determined that an alternative to manual plotting, by which aircraft position could be checked through use of aircraft FMS-driven navigation displays and indications, would provide for an equivalent level of safety.

So if you think you have an aircraft with FMS-driven navigation displays and indications and don't want to plot, read on . . .

But you might want to also consider this from the same FAA document:

[AC 91-70B, ¶] Plotting your route on your chart will increase your situational awareness as you execute your trip through oceanic and remote continental airspace.

If, like me, you are all for increasing your situational awareness, head on over to Plotting (Old School).



Figure: Example plotting chart before a crossing, (From Eddie's collection)

You Really Should Plot

The new AC 91-70 gives a non-plotting option but before it gets there, it encourages the old school method with that classic FAA word "should." (Meaning you don't have to, but you really ought to.)

[AC 91-70B, ¶] You should use a chart, of appropriate scale, to provide yourself with a visual presentation of your intended route, regardless of your type(s) of long-range navigation system (LRNS). Plotting your route on your chart will increase your situational awareness as you execute your trip through oceanic and remote continental airspace.

[AC 91-70B, ¶] Your chart should include, at a minimum:L

  1. The route of your filed flight plan or currently effective route clearance.
  2. Clearly depicted waypoints using standardized symbology.
  3. Graphic depictions of all ETPs.
  4. Alternate airports.
  5. Proximity of other adjacent tracks.
  6. Note: For certificated operators, if OpSpec/MSpec A061 has been issued authorizing use of an Electronic Flight Bag (EFB) and the principal inspector (PI) has authorized “interactive plotting for oceanic and remote continental navigation,” the EFB application may be used in place of a paper plotting/orientation chart. The current edition of AC 120-76, Guidelines for the Certification, Airworthiness, and Operational Approval of Electronic Flight Bags, provides guidance for operators to develop associated EFB procedures. For part 91 operators, an EFB may be used, provided the criteria and considerations of the current edition of AC 91-78, Use of Class 1 or Class 2 Electronic Flight Bag (EFB), are observed.

[AC 91-70B, ¶] You can use various additional techniques in order to verify that the correct points are loaded for your planned route. Verify the total route distance in your FMS against your master document to help find embedded mistakes. You should also cross-check course/headings and distances between each waypoint to ensure the FMS routing matches your master document. Referencing your plotting or orientation chart here can also be beneficial.

But if you aren't going to plot, you should at least do this . . .

[AC 91-70B, ¶D.2.9.2] Ten Minutes After Waypoint Passage. Cross-check navigational performance and course compliance by one of the following methods:

The old school method . . .

D.2.9.1 The “plotting” method is appropriate for all aircraft navigation configurations.

  1. Verify your plotting/orientation chart reflects the currently effective route clearance.
  2. Plot your present latitude/longitude and record the time on your chart.
  3. You should plot your position using coordinates from the nonsteering LRNS.
  4. Investigate/take corrective action if your plotted position does not agree with your currently effective route clearance.
  5. Using the steering LRNS, verify the next waypoint is consistent with the currently effective route clearance.
  6. Verify your autopilot steering mode is in LNAV/VNAV or other appropriate mode to ensure steering to the next intended waypoint.

The new school method

D.2.9.2 The “navigation display” method is appropriate for and available for use in aircraft equipped with an operable FMS:

  1. Confirm the aircraft symbol is on the programmed route on the navigation display (at smallest scale).
  2. Check system-generated cross-track deviation or similar indication of any deviation from the programmed route of flight.
  3. This will protect you against problems between the autopilot and the FMS, but not against an improperly programmed waypoint. Let's say you entered 5230N instead of 5330N, the classic "one degree" error that will throw you 60 nm off course. Since the line drawn by the FMS on your display is looking for a latitude of 52 degrees it will draw that as a point and you will think you are on course, no matter how small the display scale is set. I recommend that if you are not going to plot, you should at the very least bring up the GPS present position display and verify you cross the correct waypoint first, and that your course to the next waypoint agrees with the master document. (Check the magnetic course, not the heading.)

  4. Using the steering LRNS verify the “TO” waypoint is consistent with your currently effective route clearance.
  5. Do not rely on the ARINC shorthand codes here. If you don't have a way of displaying the flight plan waypoints as latitude/longitude pairs, try bringing the waypoint into the scratch pad and then to a waypoint page to ensure your "TO" latitude and longitude points are correct.

  6. Investigate/take correction action to address any anomalies or unexpected deviations.
  7. Verify your autopilot steering mode is LNAV/VNAV or other appropriate mode to ensure steering to the next intended waypoint.

D.2.9.3 An alternate method may be used with FAA acceptance.


*Advisory Circular 91-70A, Oceanic and International Operations, 8/12/10, U.S. Department of Transportation

* This version of AC 91-70 has been superseded but it retained because it contains older guidance that helps place current guidance into perspective.

Advisory Circular 91-70B, Oceanic and International Operations, 10/4/16, U.S. Department of Transportation

Revision: 20170407