flight time. In addition, the typhoon centre or sub-centre planning the 

 mission always requests that the mission be flown at an altitude and by 

 the method which will provide the most useful weather data for their 

 particular need. 



Reconnaissance procedures involving tropical disturbances are such 

 that two procedures are actually used, depending on whether investigation 

 of a storm or typhoon is to be made. 



In storm or search reconnaissance the flight altitude to the storm 

 area will be made at 1,500 ft. Flight altitude within the storm area is 

 the pilot's choice within feasible operational limits. 



Upon entering the circulation of the storm a heading ^^'ill be maintained 

 that will keep the wind to the left of the aircraft or at an angle of 90° 

 from the wind-flow. If the wind is due west the heading will be north. 

 If due east the heading will be south. 



■ Such a heading will normally take the aircraft to the storm's centre. 

 However, if the centre of the storm is difficult to locate an alternate 

 plan is used. This method is to assume a heading with the wind so as 

 to partially circumnavigate the storm. To do this a heading with the 

 wind is assumed, and this heading maintained until the wind has backed 

 to 40 or 50 degrees from the tail and to the right of the aircraft. Then 

 the aircraft's heading is changed so as to again fly parallel with the wind 

 until the wind again backs 40 or 50 degrees from the tail and to the 

 right. This procedure, if accomplished on from two or four legs, will 

 enable the navigator to fix the centre by triangulation. The aircraft 

 will then proceed to that point and reconnoitre until the centre is definitely 

 established. When this is accomplished a fix will be obtained and a 

 complete observation made. The aircraft will then leave the centre 

 and complete the circumnavigation of the storm. This is usually done 

 at a radius of from 60 to 100 nautical miles of the centre. Circumnaviga- 

 tion will be made through 270 degrees so as to make observations at four 

 points equidistant from the centre and to the north, south, west, and 

 east of the centre. This ensures that all quadrants are covered and 

 gives information needed by the forecaster in predicting rate and direction 

 of movement. It is true that navigation error due to frequent heading 

 changes and rapid wind shifts will make this method difficult at times, 

 but will generally afford the desired information. 



After completing the circumnavigation the aircraft proceeds, if opera- 

 tionally practical, to the nearest staging base along the storm's expected 

 track and at an altitude of 1,500 ft. If this is not feasible the aircraft 

 will proceed from the storm in a direction predetermined by the typhoon 

 warning centre and which will give the forecasters the most useful recon- 

 naissance prior to return of the aircraft to the staging base. Flights are 

 so planned as to provide weather data to the limit of the storm's influence. 



In reconnaissance where a typhoon is known or suspected to exist the 

 flight altitude to the typhoon area will be made at the 700 millibar level. 



Observations will be made every 100 nautical miles to the typhoon 

 area. Within the typhoon, observations will be made every twenty 

 minutes, or at prescribed positions and/'or when weather encountered 

 vvarrants such observation. 



Upon entering the area of the typhoon the precedure is the same as 

 for a, storm. However, at the 700 millibar level the use of radar, pressure 

 diflerential, and visual observation of cloud formations, when possible, 

 simplify this procedure. 



14 



