5. Plain language remarks may be added at the 

 end of the message to supplement the coded 

 message or to supply additional information 

 not provided for in the code. 



6. The solidus (/) will be used to report missing 

 or unknown data unless otherwise specified 



for the individual elements. The term "altitude" 

 is defined as the vertical distance of a level 

 point or an object considered as a point, 

 measured from mean sea level. 



7. If operational data or position reports are 

 required, they will be transmitted by the air- 

 craft prior to the 9xxx9 key group of the RECCO 

 report. These additional operational reports 

 will not be included in the landline teletype- 

 writer transmission of the RECCO report. 



SECTION 1 • MANDATORY Section of the 

 Flight Level Portion of the 

 Message . 



8. 9xxx9 - The key group 9xxx9 indicates the 

 dimensional unit being used and whether or 

 not radar observations are being made. This 

 group shall always be included in the report. 



If radar equipment is operational, this informa- 

 tion shall be reported for symbol "xxx" even 

 though no echoes are observed. The omission 

 of the 8-groups from the report will indicate to 

 the recipient that no echoes were observed. 

 (Note: The units indicated by symbol "xxx" 

 apply only to the flight level portions of the 

 message. All altitudes of standard pressure 

 surfaces and tropopause reported in the sound- 

 ing portion of the message are given in meters 

 and decameters in accord with the instructions 

 given in the Manual for Radiosonde Code for 

 reporting sounding data.) 



9. GGgg and Y - The time the aircraft is on the 

 vertical axis of the observation cylinder is 

 reported for "GGgg". All elements are observed, 

 insofar as practicable, when the aircraft is at 

 the point of observation or in proximity thereto. 

 The actual time of observation is the time at 

 which the observing of all elements is completed. 

 All times (GGgg) and the day of the week (Y) are 

 given in Greenwich Mean time. The day reported 

 for Y is the day on which the observation is 

 taken and NOT the day on which it is transmitted. 



10. LgLgLg and L L p L - The latitude and longitude 

 of the point, at wnicn the flight level observation 

 is made, are reported for "L a LgL a " and "L,L L " 

 respectively. Tenths of a degree are obtained by 

 dividing the number of minutes by 6, disregarding 

 the remainder. The hundreds digit is omitted 

 from longitudes 100° to 180° , inclusive. 



11. B - The type of turbulence encountered at the 



time of observation is reported for "B". Definitions 

 of the terms used to indicate the various types of 

 turbulence reported are: 



Light - A turbulent condition during which 

 occupants may be required to use 

 seat belts, but objects in the aircraft 

 remain at rest. 



Moderate - A turbulent condition in which 

 occupants require seat belts and 

 occasionally are thrown against 

 the belt. Unsecured objects in the 

 aircraft move about. 



Severe - A turbulent condition in which the 

 aircraft momentarily may be out of 

 control. Occupants are thrown 

 violently against the belt and back 

 into the seat. Objects are secured 

 in the aircraft are tossed about. 



12. f' - The average flight condition existing during 

 trie time required to make the flight level observa- 

 tion is reported for "fj. ". 



13. hhh - The true altitude of the aircraft at the 

 time of the flight level observation is reported 

 to the nearest hundred foot or 30 meter level 

 (e.g., when the aircraft is 50 feet or more above 

 a hundred foot level the next higher level is 

 reported for "hhh"). 



14. d| - When code figure 9 is reported, the distance 

 over which the wind is averaged is added at the 

 end of the message in plain language. 



15. d and ddfff - When code figure 8 is reported 

 for "d a ", five solidi (i.e., /////) are reported 

 foj the "ddfff" group. The complete specifica- 

 tions for Table 7 are: 



TABLE 8: d a 



90% to 100% reliable. Multiple drift 

 with closed wind star, or small 

 open star when winds are 50 kts 

 or greater. Short radar wind runs. 



1 75% to 100% reliable. Multiple drift 



with small open star or double 

 drift or single drift with average 

 ground speed by timing. Short 

 radar run. 



2 80% to 100% reliable. Fix to fix 



winds using the following pin 

 point visual fixes, radar fixes 

 or accurate loran fixes using 

 good ground waves. 



3 75% to 90% reliable. Fix to fix 



winds using two or three lines 

 of positions (LOPs) either 

 loran, celestial, radio or sight 

 bearings or any combination of 

 the three above when all lines 

 of position are considered re- 

 liable. 



4 60% to 80% reliable. Winds obtained 



using single drift and single 

 LOP (Speed Line), air-plot, etc. 



5 50% to 75% reliable. Fix to fix 



winds using two or three lines 

 of position either loran, cel- 

 estial, radio or sight bearings 

 or any combination of the above 

 when one of the lines is not 

 considered reliable. 



6 Less than 50% reliable. Winds ob- 



tained by any of the above 

 methods which the navigator 

 believes to be inaccurate or 

 of questionable accuracy. 



7 No reliability. Assumed or esti- 



mated winds. 



8 No wind. Navigator unable to deter- 



mine a wind. 



9 Not used. 



16. TT - Free air temperature (corrected for 

 calibration, installation, and dynamic 

 heating effects) at flight level (hhh) at the 

 time of observation is reported for "TT" 

 to the nearest whole degree Celsius. 



When the temperature is below zero, 50 

 is added to the absolute value of the 

 temperature and the sum is reported 

 for "TT". The hundreds figure, if any, 

 resulting from this addition is disre- ■ 

 garded. 



17. TjTj - When the wet bulb temperature is 

 below -35°C., "//" is reported for "TjjT^". 

 Dew point is used to indicate the moisture 

 content of the air in United States RECCO 

 reports. (See Note 16.) 



18. w - The specification most descriptive of 

 the weather existing at the time of observa- 

 tion is reported for "w". Code figure 2 is 

 reported when the total amount of cloud 

 above or below the aircraft is 7/8 or more. 



19. m - The information which best amplifies 

 the present weather reported for "w" is 

 reported for "m". 



SECTION 2 - OPTIONAL Section of the 

 Flight Level Portion of the 

 Message 



i iioiNo - If data on more than three lay- 

 ir cloud are reported, a second 



20. lk n N ] N,N 

 ers o 



Ik^N^Nj group plus the required number of 

 ChnHH groups are inserted in the message 

 following the last of the first three ChhHH 

 groups. The additional number of layers 

 (i.e., exclusive of the first three layers) 

 being reported is given for "k n " in the 

 second Ik^N^ group. The coverage of the 

 additional cloud layers is reported for 

 Nj, No, and N 3 in the second group, as re- 

 quired; When no clouds exist the IkpN^N^ 

 and ChhHH groups are omitted from the mess- 

 age. 



21. k n -When clouds are present in indefinite 

 layers (chaotic sky) code figure 9 is re- 

 ported for "k ". If it is impossible to 

 determine that clouds exist (due to dark- 

 ness or for other reasons) a "/" is re- 

 ported for "k ". When a cloud layer is 

 present but data on the type, the extent 



of coverage, and altitude can not be obser- 

 ved, "/'s" are reported for N, C, hh, and 

 HH, as appropriate; however, the layer will 

 be included in the number of layers report- 

 ed for "k n ". (See Note 22.) 



22. Nj^.N, - The amount of cloud reported 

 for Nj^, etc., is the amount in the 

 individual layer as though no other cloud 

 were present; i.e., the summation Concept 

 is not used. The cloud layers are reported 

 in the message in ascending order according 

 to altitude of the base. When code figure 



9 is reported for "k n ", the value reported 

 for "Nj" is the total amount of cloud cov- 

 erage present and "//" is reported for 

 "NoN 3 ". When a "/" is reported ft)r "k " 

 "999" is reported for "NiNoN,". (£ee Note 

 21.) 6 



23. ChhHH - This group is included in 



Ithe mess- 



age for each layer of clouds reported by 

 "k" and described by N, , N 9 , etcj 



24. C - The type of cloud predominating 

 layer is reported for "C" 



in the 



25. hh and HH - The average altitude of both 

 the base and top of the cloud layer report- 



ed for "C" is reported for "hh" and 

 respectively 



"HH" 



26. 4ddff and 5DFSD K - Surface data aje report- 

 ed in this group. Surface wind data are 

 included in each low level report. Either 



or both of the groups may be included in 

 the message if required. 



27. dd - The estimated direction (true) FROM 

 which the surface wind is blowing is re- 

 ported for "dd". (See Note 28.) 



28. ff - The estimated speed of the surface 

 wind is reported for "ff". In the range 



of 100-199 knots, inclusive, the hundreds 

 figure is omitted and the tens and the 

 units values are reported for "ff" and 50 

 is added to the value normally reported 

 for "dd". For speeds in excess of 199 

 knots, "//" is reported for "ff" and .the 

 actual speed is reported in plain lan- 

 guage at the end of the message. 



29. D - The estimated direction (true) FROM 

 which the surface wind is blowing is re- 

 ported for "D". 



30. F - The estimated force of the surface 

 wind is reported. When the speed exceeds 

 Force 9, code figure 9 is reported for 

 "F" and a plain language remark is added 

 at the end of the flight level portion of 

 the message giving the actual Beaufort 

 Force as "GALE TEN", "STORM 

 ELEVEN", or "HURRICANE TWELVE". 



31. D K - The true direction FROM which the 

 swell is moving is reported for "D^". 

 Code figure is reported for "no swell" 

 and code figure 9 is reported to indicate 

 "confused" swell. When the waves are 

 from several directions, the direction 

 from which the wave of longest period is 

 traveling is reported. 



32. 6W S S S W C D W - Two 6-groups may be included 

 in the message to report two significant 

 weather changes, and/or two weather phen- 

 omena off course, or combinations thereof. 



33. W s • Significant weather changes which 

 have occurred since the last observation, 

 or in the preceding hour (whichever period 

 is shorter) along the track of the aircraft 

 are reported for "W s ". 



34. S. - The distance from the present posi- 

 tion back to the location of the signifi- 

 cant weather change (W.) is reported for 

 "S<". 



35. W. -Any off-course weather condition of 

 importance which is not included or implied 

 in the specification reported for present 

 weather, will be reported for "W c ". The 

 information reported for "W c " supplements 

 the present weather (w). (See Notes 2, 18, 

 54 and 55.) 



36. D w - Code figure 9 indicates "in all direc- 

 tions". 



37. 7l r l t S b S e 7h j h j H i H j -When icing occurs, 

 both of the 7-groups shall be included in 

 the report. The 8-groups may be repeated 

 as often as necessary to describe the ic- 

 ing conditions encountered. 



38. I r - Normally only aircraft equipped with 

 icing rate meters will report code figures 

 through 6; however, if a quantitative 

 estimate is possible it may be reported 

 even though the aircraft equipment does 

 not include a meter. In general, code 

 figures 7 through 9 are used more often 

 than the other code figures. 



United States definitions of the terms 

 given in Table 21 used to describe the 

 rate of ice accumulation are: 



Light - An accumulation of ice which 

 can be disposed of by the air- 

 craft de-icing equipment, 

 which presents no serious 

 hazard to the flight, and 

 which us not sufficient to 

 cause alterations in speed, 

 altitude, or track. 



Moderate - An accumulation of ice which 

 produces a condition inter- 

 mediate between "light" and 

 "heavy". 



Heavy - An accumulation of ice which 

 continues to increase despite 

 operation of de-icing equipment, 

 which is sufficiently serious to 

 cause marked alteration in speed, 

 altitude, or track, and which 

 would seriously affect the safety 

 of the aircraft. 



39. If - For this purpose a non-persistent con- 

 trail is defined as one which is 1/4 nautical 

 mile or less in length and a persistent con- 

 trail is one which is over 1/4 nautical mile 

 in length. 



40. S fa - Code figure is reported when the air- 

 craft has completed an ascent or a descent, 

 in which case the limits of icing are re- 

 ported in group 7hjhjHjHj. Code figure 2 



is reported when the icing began during the 

 time of the flight level observation and it 

 will be an amplification of the information 

 reported for "w" and "m". 



41. S e - Code figure 2 is reported when the ic- 

 ing is continuing at the time of the flight 

 level observation. 



42. hjhj - When the aircraft encounters icing 

 during an ascent or descent, the altitude 

 of the base of the icing stratum is report- 

 ed for "hjh:". When the aircraft encount- 

 ers icing during level flight, the altitude 

 at which icing occurred is reported for 



"W- 



43. HjHj - When the aircraft encounters icing 

 during an ascent or descent the altitude of 

 the top of the icing stratum is reported 



for "HjHj". When the aircraft encounters 

 icing during level flight, "//" is report- 

 ed for "HjHj". 



44. 8d|d r S r O e 8w g a c e i e - When radar data are 

 observer/, both the 8-groups shall be in- 

 cluded in the report. The 8-groups may be 

 repeated as often as necessary to report 

 essential data. 



45. d f d - Code figure 99 is reported to indi- 

 cate echoes "in all directions". (See 

 Notes 8 and 44.) 



46. S - When the distance to the center of the 

 echo is greater than 95 nautical miles, 100 

 is subtracted from the distance and the tens 

 value of the remainder is reported for "S r " 

 and 50 is added to the value normally report- 

 ed for "d r d ". When a line of echoes is 

 observed, ,f S r " is the distance to the mid- 

 point of the line. 



47. c - The term solid is used when the indi- 

 vidual echoes are not distinctly and widely 

 separated. Code figures 1, 2, 5, and 6 are 

 used to report circular areas of echoes. 



SECTION 3 • Intermediate Reports 

 (OPTIONAL ) 



48. When required, intermediate observations may 

 be taken between complete flight level obs- 

 ervations. The intermediate data are report- 

 ed in the next complete flight level message 

 by inserting the coded groups (i.e., Section 

 3) in the message immediately following the 

 last coded group of the complete flight level 

 report. Section 3 may be attached at the end 

 of either Section 2 or Section 1, as appro- 

 priate. 



49. The use of Section 3 is OPTIONAL. If this 

 Section is reported, all of the data groups 

 (i.e., GGggi u through mjHHH) shall be always 

 included in the message for each intermedi- 

 ate observation being reported with appro- 

 priate missing indicators being used for 

 those elements for which datum is not avail- 

 able except the (4L a L a L L ) group. The self- 

 identifying 4-group may be included or omit- 

 ted as required. 



50. The intermediate data groups are extracted 

 from the complete flight level form as 

 follows: 99999 GGggi u ddfff TTT u T u w 



mjHHH (4L a LgL L ) GGggi u ddfff 



etc 



51. Unless otherwise indicated it shall be as- 

 sumed that a straight-line constant-altitude 

 flight has been made between the position of 

 the last reported complete flight level obs- 

 ervation and the present one. Any inter- 

 mediate observations reported in the present 

 complete flight level report shall be assum- 

 ed to have been made on this flight patch. 



52. If the direction of the flight has been alt- 

 ered, the latitude and longitude of the turn- 

 ing point shall be reported by the group 



( 4L a L a L oL )- The group (4L a L a L L ) 

 shall be inserted in the Intermediate 

 Reports portion of the message, as appropri- 

 ate, with respect to time. 



53. If the altitude of the flight is altered be- 

 tween any two consecutive complete flight 

 level observations, intermediate observa- 

 tions shall not be reported between those 

 two flight level reporting positions. 



Plain Language Remarks 



54. Plain language remarks may be added at the 

 end of the message to supplement the coded 

 data or to supply additional information of 

 importance not provided for in the code. For 

 example: Time of occurrence of significant 

 weather (W s ), past weather, etc. 



55. If information on past weather is added as a 

 plain language remark, the most significant 

 weather encountered since the last report, 

 or in the last hour, whichever period of 

 time is shorter, shall be described by the 

 remark. 



Sounding Portion of the Message 



56. Sounding data are obtained during vertical 

 ascents or descents of the aircraft or by 

 releasing dropsondes from the aircraft. For 

 transmission purposes these data may be add- 

 ed to Section 2 of RECCO or sent as a sepa- 

 rate message. 



57. Vertical ascent or descent. WMO code form 

 FM 35.C (TEMP) shall be used to report 

 sounding data obtained by means of either 

 a vertical ascent or descent. 



a. If the sounding data are added to the 

 flight level report, they shall be 

 added to Section 2 of RECCO and iden- 

 tified by the indicator group 17171. 

 In this instance the groups MjM, and 

 (ll)iii shall be omitted from FM 35.C 

 and the group GGh^hjh, shall become 

 00hjhjh,hi. The form being 



8w a cj 17171 



JiJiWxi) Wi) 



rornilnii/jflo 6IC, 



In this instance the time and position 

 of the ascent or descent shall be 

 given in groups GGggi u YOLLgL, 

 L.L LgBf,; of the flight level report. 



When the data obtained by means of a 

 vertical ascent or despent are sent as 

 a separate report, the first four 

 groups of Section 1 of RECCO shall be 

 followed by FM35.C as follows: 9xxx9 

 GGggi.. YQLL.L, L.L.LBf; 17171 



■u Y^L-a 

 etc. 



o c 



58. Dropsonde. Sounding data obtained from a 

 drop-sonde released from the aircraft shall 

 be reported by means of WMO code form FM 

 36.C (TEMP SHIP). The drop-sonde data may 

 be added either to the flight level report 



or sent as a separate report. 



a. When the drop-sonde data are added to 

 Section 2 of RECCO the indicator group 

 71717 precedes the coded sounding data 

 (FM 36. C). In this instance two minor 

 alterations are made in FM 36. C, the 

 MM: group is omitted from the report 

 and GG is reported to the nearest 

 quarter hour. The nearest quarter of an 

 hour is indicated by adding 25, 50 or 



75 to the actual number of hours. 



When the minute lies between 52 1/2 

 and 07 1/2 minutes, nothing is added 

 to the hour; e.g., times between 

 0152 1/2 to 0207 1/2 are coded 02. 

 When the minute lies between 07 1/2 

 and 22 1/2 minutes, 25 is added to 

 the hour; e.g., times between 

 0307 1/2 to 0322 1/2 are coded 28. 

 When the minute lies between 22 1/2 

 and 37 1/2 minutes 50 is added to the 

 hour; e.g., times between 1122 1/2 to 

 1137 1/2 are coded 61. When the min- 

 ute lies between 37 1/2 to 52 1/2 

 minutes 75 is added to the hour; e.g., 

 times between 2037 1/2 to 2052 1/2 

 are coded 95. 



b. When the drop-sonde data are sent as 



a separate report, the TEMP SHIP form 

 of message (FM 36. C) is preceded by 

 the key groups 9xxx9 and 71717. 



c. The location and time (to the nearest 

 quarter hour) at which the drop-sonde 

 was ejected from the aircraft shall 



be given in the YO^L-, and L L L GG 

 groups of TEMP SHIP (FM 36.C). 



59. Following are general notes which apply to 



the coding of sounding data obtained by 

 aircraft: 



a. Whenever practicable extrapolated data 

 are reported for P P P , T T and 

 T(J Tj If extrapolated data are not 

 available for these elements, the sur- 

 face groups are omitted from the report. 



b. If tenths values of air and dew point 

 temperatures are not reported, a zero 

 is coded for T xo , T^, T^, etc. 



60. Sea Ice Data : 



Sea ice, as observed by aircraft, are re- 

 ported in the national code from (see 

 Chapter III, Part A-4-RECCO). 



