Using TAFS For Flight Planning

METEOROLOGY FLIGHT PLANNING

CHAPTER ONE

4th Line -- From 1700Z (BECMG 1718) up to but not including 0200Z (FM02), winds from

230 at 15 knots with gusts to 25 knots (23015G25KT), visibility same as 3rd line (9999), clouds

same as 3rd line (SCT025CB, SCT250), moderate turbulence in clear air from surface up to 4000

feet (530004), altimeter setting same as 2nd line, 29.96 inches (QNH2996INS).

5th Line -- Temporarily between 1900Z and 0200Z (TEMPO 1902), winds same as 4th line

(23015G25KT), visibility five miles (8000 meters), with thunderstorms and rain showers

(TSSHRA), scattered clouds at 1000 feet AGL (SCT010) and broken cumulonimbus clouds at

2500 feet AGL (BKN025CB), turbulence same as 4th line (530004), altimeter same as 2nd line

(QNH2996INS), with ceiling at 2500 feet.

6th line -- From 0200Z (FM0200) up to but not including 0900Z (end of TAF), winds from 270

degrees at 10 knots (27010KT), visibility greater than 6 miles (9999), scattered clouds at 3000

feet AGL (SCT030), broken clouds at 8000 feet AGL (BKN080), broken clouds at 25,000 feet

AGL (BKN250), altimeter setting 30.01 inches (QNH3001INS), ceiling at 8000 feet AGL,

minimum temperature forecasted for the day is 20 C (68 F) at 0900Z.

113. USING TAFS FOR FLIGHT PLANNING

For flight planning purposes, an aviator must consider the worst weather conditions that fall

within the period of 1 hour prior to the planned estimated time of arrival (ETA) up to but not

including one hour after ETA, for a total of a two hour window. As an example, assume an ETA

of 1620Z at NAS Whiting, use the TAF in Figure 1-28, and follow these simple steps:

Determine the arrival window, which would be 1520 1720Z in this case.

Evaluate the whole TAF to determine the forecast time period to which each line

applies. If any part of the two hour ETA window falls within the time period of that

line, then the information in that line will be applicable. In this case, lines 2, 3, and 4

each cover part of the 1520 1720Z window.

Finally, mix and match the weather from each line for use in flight planning, building

a set of the worst-case scenario for each group: strongest winds, lowest visibility,

worst weather, lowest ceiling, and lowest altimeter.

Another technique is to lay out a timeline in order to dissect and categorize the applicability of

the various lines of a TAF. By drawing labeled brackets around the times to which each line

applies and around the two hour ETA window, it becomes easier to see which lines of the TAF

are applicable. This technique is especially useful when planning a mission with numerous

approaches or en route delays, or when the weather will be a deciding factor for the landing time.

Figure 1-38 shows a diagram of this technique for our example.

AVIATION ROUTINE WEATHER REPORTS AND TERMINAL AERODROME

FORECASTS 1-33