Landfall Navigating

Copyright ©2009 by Paul Niquette. All rights reserved.
Intentional OffsetOne solution to the puzzle is shown in the schematic flight plan on the right.  It calls for deliberately taking up a heading to the right of the direct course by an angle that corresponds to the maximum expected steering error during the over-water flight. 

Doing that removes all ambiguity about which way to turn if the destination is not immediately identified upon reaching the shoreline: Specifically one simply turns left and follows the shoreline. 
The phrase Landfall Navigating has been appropriated from nautical terminology for the solution to this puzzle.

Obviously, the course line could have been intentionally offset to the left, with turning to the right after completing the over-water flight.  The decision about which plan to adopt may be influenced by several factors...

  • angle of the shoreline with respect to the course line;
  • landmarks along the shoreline available for confirmation;
  • reported weather conditions and visibility at the destination;
  • direction of the winds aloft and at the surface;
  • terrain surrounding the airport, if it is inland.
The term 'landfall' can be used as a metaphor for any elongated geographical feature on the surface that crosses the course line.  Here is a real-life case drawn from memory of a flight in the 1980s before GPS came along to revolutionize avigation. The two-hour flight originated north of Monterey in California with a destination at South County Airport in San Martín.  An afternoon overcast concealed the ground west of the coastal foothills, and haze in the valleys toward the east limited visibility to about a mile. 
The navigation chart above shows the destination located adjacent to Highway 101, which runs roughly north and south between Morgan Hill and Gilroy.  PAJAR is a low frequency radio beacon located near Watsonville on the Pacific Coast.  The pilot/puzzler might have decided to use PAJAR for homing, then turn toward the northeast, taking up a heading of 045 dead reckoning directly to South County. 

Having departed PAJAR, the flight was subject to the indicated course errors, such that at the extremes the planned route would cross Highway 101 too far away to see the airport runway on either side of the plane. The red arrows show the possibilities of turning the wrong way. The distance for that leg was only 14 nautical miles.  With a full hour of fuel on board, the situation hardly presented any kind of danger. 

Turning the wrong way, though, would have been an embarrassment for the pilot.  After more than two hours aloft, my passengers, for personal reasons, were eager to get on the ground.

Accordingly, I decided to apply Landfall Navigating by taking up a heading of 055 (10 degrees to the right of the intended course) thereby obviating a turn away from the airport, as indicated by the green arrows in the sketch on the right. 

The procedure will often be advisable even when the pilot has no visible "landfall" line but instead an elapsed time flying at a known groundspeed from some previous fix. 

Consider the case of dead reckoning to a waypoint surrounded by desert or a small island in the middle of an ocean.  Expect to see Landfall Navigating featured in Live Reckoning, another in a series of puzzles that concludes with Which Way Amelia?  Along the way, sophisticated solvers may actually solve the most famous puzzle in aviation history.

TIGHAR Earhart Project used by permission

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