What is that "NO" on the flightpath plot released by the FBI?
(re.
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It isn't "NO." It's a repaired "NB."
The full flightpath plot was made in three pieces which were then stuck together. Each piece was plotted on an aeronautical chart. The piece that had 44°N through 46°N was cut off along a constant-latitude line about 1/4 minute north of the 46°N line. This piece was then pasted down on top of the corresponding part of the piece that covered 46°N and northward. This covered up material that was on the latter (northern) piece of chart.
The material that was covered up is apparent from magnifying the 46°N vicinity of the higher resolution flightpath plot we've discussed some in the past. It includes part of a state name. It includes arrows for time annotations that had been written on the northern piece of chart. And, it includes the lower part of the "NB" that had been written on that piece of chart.
After the central chart piece was stuck on the more northern piece, someone replaced the part of the "B" that had been covered but did not replace the covered part of the "N." And the replaced part of the "B" was done with a narrower, less dense marker.
What about the meaning of "NB"?
The "B" means that the 1°x1° quadrangle in which "NB" appears is in a 1° wide band of latitude that is the second such band north of the latitude baseline (45°N) of zone DK. The "N" means that the quadrangle is in a 1° band of
longitude that is the 13th band starting from the western baseline (135°W longitude) of that zone DK. To those who know the coordinate system, the "NB" means the 1°x1° quadrangle is the one lying between 46°N, 123°W and 47°N, 122°W. By convention the code was placed in the lower left corner of the quadrangle.
A couple of questions are obvious. What's that "zone DK"? And, why all the complexity? You can look right on the chart and see that the 1°x1° quadrangle lies between 46°N, 123°W and 47°N, 122°W. First question first.
This is all part of a thing called the "world geographic reference system," conventionally abbreviated "GEOREF." This obsolete system was used by the air force and army air force. It is pretty much equivalent to latitude and longitude except that it identifies areas, rather than points, and cannot be nearly as precise.
In the system, the longitudes of the world are divided into 24 15°-wide bands of longitude eastward from the 180° longitude meridian. These bands are assigned letters from A to Z, excluding I and O, starting at the band on the east side of 180° longitude.
Similarly,
latitudes are divided into twelve 15° bands which are assigned letters A to M starting at the band adjacent to the south pole.
The intersections of the 15°-wide latitude bands and longitude bands creates zones which are 15°x15° quadrangles which are uniquely identified by the letter for the longitude zone followed by the letter for the latitude zone.
Using this system, the fourth longitude band (designated "D") would extend from 135°W to 120°W and would encompass the areas with which we are concerned. Latitude band J would be 30°N to 45°N and would encompass the areas of the flightpath south of about Salem, OR and latitude band K would be 45°N to 60°N and would encompass the areas
north of Salem. Hence the areas south of Salem would be in 15°x15° quadrangle (zone) DJ and the areas to the north would be in zone DK.
This system also includes breaking each of the 15° bands (lat and lon) into 15 1°-wide bands. These then are assigned letters A to Q (skipping I and O) from the south and from the east. Because the longitudes between 123° and 122° are the 13th band, the longitude band is assigned letter "N," and this is the first letter of the identifications of all the 1°x1° quadrangles in the areas of the flightpath. The three quandrangles north of 45°N are DKNA, DKNB and DKNC. The system uses 2 letters to identify large quadrangles, plus 2 more letters to identify the smaller quadrangles within the large ones.
The three 1°x1° quadrangles south of 45°N are the 13th, 14th and 15th in the "N" longitude zone of 15°x15° quadrangle DJ, so they are DJNN, DJNP and DJNQ. The "NP" was not marked on the lower half of the complete flightpath plot, but the "NN" and "NQ" were. So the NN and NQ on the plot are not "in sequence" with the NA, NB and NC in the upper half of the plot because they are in a different 15°x15° quadrangle than the NA, NB and NC.
So, to the second question. Why put the notations on the chart?
The notations are conspicuous. They were put on the separate pieces before the pieces were put together and served to make it easy and quick for the people who put the pieces together to put them together in the right sequence. It was an assembly aid. Those people were accustomed to the GEOREF system. Up until about 1971 the quadrangle identifications had been preprinted on the airforce edition aero charts the people were accustomed to using. Those charts also included explanations of how to use the system to identify and reference 1-minute by 1-minute geographical areas.
