SYMPOSIUM ON GENERAL METEOROLOGY OF 



THE PACIFIC IN TEMPERATE AND 



HIGHER LATITUDES 



PRESSURE PATTERN FLIGHT PLANNING OVER THE PACIFIC 

 By Irving Gringorten, 

 Base Directorate for Geophysical Research, U.S. Air Force 



Introduction 



" Pressure pattern flying " is a generally accepted term to describe a 

 S3'stem of navigation by air over long distances so as to take advantage 

 of the existing wind fields. Since most flying has been over the temperate 

 latitudes, where the winds can be assumed to be geostrophic, it had been 

 found convenient to work with the known pressure fields instead of 

 wind fields. However, at this conference, where we are engaged in the 

 problems common to all countries that border upon the Pacific Ocean, 

 from equatorial to both polar regions, it would seem more appropriate 

 to call this subject " wind pattern flying," because the winds cannot 

 be assumed to be given by the pressure fields for about 20° of latitude on 

 either side of the Equator. " Wind pattern flying," therefore, will be 

 considered the subject of this paper. 



In the past there have been several methods frequently used in wind 

 pattern flying. Some airlines that schedule trans-oceanic flights define 

 six or seven simple tracks between point of departure and destination, 

 and then use a rapid method for finding which of the tracks requires the 

 least flying time. 



Some airlines use another method of navigation, known as " Single 

 Heading Fhght," in which the airplane is kept on one precomputed 

 heading from point of departure to destination. Such navigating has 

 had several advantages. But the essential advantage of single heading 

 flight is in the saving of flying time. This is accomplished because the 

 forward motion of the airplane is not cut down by the airplane's crabbing 

 into the wind. In order to stay on the straight-line path between point 

 of departure and destination, the airplane must first of all crab to the 

 left, then crab to the right, then head-on course, and so on. But, by crab- 

 bing to the right or to the left, the forward speed is only a component 

 of the airplane's total airspeed. On the other hand, in single-heading 

 flight, there is little or no crabbing, so that the forward motion is practi- 

 calty the full airspeed of the airplane. 



But there are several limitations to the use of single-heading flight 

 as it has been practised so far. First of aU, the one proper heading 

 has been computed from the existing or forecast pressure fields, instead 

 of the wind fields, it having been assumed that the winds are geostrophic. 

 This assumption is not true for flights that cross or come near the Equator. 

 Secondly, there has been no adequate method of plotting the expected 

 path of the airplane. Thirdly, if the flight be long, say 3,000 nautical 

 miles, then the use of a single heading in itself oft'ers no advantage of 

 simplicity to the navigator, unless the heading is a single magnetic 

 heading. (In this latter case the navigator would keep only one reading 

 on his magnetic compass.) But in the past single heading has implied 

 single true heading with respect to geographic north. 



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