Wind Analysis
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CHAPTER TWO
INTERMEDIATE FLIGHT PREPARATION WORKBOOK
d.
DME greater than the thousands of feet of aircraft altitude.
2.  Once these conditions are met, there are two methods of computing GS. One is to check
the DME at 1, 2, or 3-minute intervals. Since the DME readout is digital, the one-minute check
is accurate and GS can be determined by multiplying the DME flown by 60. Another method is
to take a 36-second check and add a zero to the end of the DME difference. If this check is
continued to the 1-minute mark, GS in both knots and Nautical Miles per Minute (NM/min) can
be obtained without calculation (and can be used for cross-checking).
3.  At the completion of the first GS check and every leg thereafter (once the GS readout is
valid), the student must give an updated ETA at the next point and estimated fuel remaining at
the IAF.
Wind Analysis
The headwind/tailwind component is determined by taking the difference between TAS and GS.
The crosswind component is determined by the crab angle. The amount of wind that equates to
1° of crab can be determined by dividing the TAS by 60. If the TAS is 420 KTS then 1° of crab
equates to 7 KTS of crosswind. This is called the Guide Number. A quick method of
determining wind is to take all of the larger component and half of the smaller to determine
velocity and use vector analysis to determine direction (see the Trainee Guide for Visual
Navigation CNATRA P-811). At 420 KTS TAS, for example, if it takes 7º of left crab to
maintain a course of 360° with a GS of 390 KTS, the wind can be determined this way:
1.
7 KTS/1° of crab x 7º of crab = 49 KTS crosswind
2.
390 KTS GS - 420 KTS TAS = 30 KTS headwind
3.
The resulting wind is 300 at 65 knots (rounded to the nearest 5 KTS).
Lead Points
During flights, all turns greater than 30o (including Pt.-to-Pt.) will be led. To calculate the lead
point for a 90º turn, use minimum DME + 1% of GS over NAVAIDS and 1% of GS at fixes.
Consequently, 45º and 30º turns are led by 1/2 of 1% and 1/3 of 1% of GS, respectively.
Example: Calculate the lead point for an aircraft at FL 350, 450 KTS GS, making a 90º turn
over a NAVAID.
1.
Minimum DME =
35,000/6000 =
5.8 DME
2.
1% of GS =
0.01 x 45 =
4.5 DME
3.
Lead point
10.3 DME
2-10
T-1A FLIGHT PROFILES

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