Figure 4. Computing Ground Speed with Crab Angle Less Than 10 Degrees (part 1)

T-45C TS INav-08

Fuel, Weather, and Alternate Airfield Planning

You will be primarily working with the FLIP Enroute High Altitude Charts which depict radials (courses) in

degrees magnetic. These are the radials you set in the course selector of the HSI. You will fly a

magnetic heading on your HSI to make good the course, or track-over-the-ground, you have selected.

Therefore, in flight planning, if you are faced with TRUE WINDS and MAGNETIC COURSES, it is

obvious something has to be done to make them compatible.

The circular computer solves this by providing a magnetic-true conversion scale on either side of the

True Course (TC) index. From the FLIP Enroute Charts, you obtain your desired Magnetic Course and

also the Magnetic Variation in the area. By setting the Magnetic Course on the “Degree Scale” over the

Variation (East or West), the wind dot is automatically aligned to use the True Winds Aloft which you

received from the forecaster. You use this method for each leg to compute groundspeeds for each leg of

flight.

NOTE: Lines of Magnetic Variation are depicted at 4 degree intervals. You should interpolate between

lines to obtain the approximate variation in your area of flight or an alternate method would be to look at a

field diagram in the area of flight.

Examples:

Computing ground speed with crab angle less than 10 degrees - You obtain the following

information to complete one leg of flight on the Jet Flight Log:

GIVEN:

TAS

OPPOSITE 340 KTAS

Figure 4 (Part 1): COMPUTING GROUND SPEED

WITH CRAB ANGLE LESS THAN 10 DEGREES

(2-02) Original

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