How to use Winds Aloft temperature
 

Hi everyone,

I need your help clarifying something that I'm having a brain fart on. I'm practicing on doing a flight plan the old school way and while I understand that there are some programs out there like Foreflight, Skyvector, etc., I like to do it manually from time to time to keep the skills up. Anyway, I'm flying a C-172 cruising at 5,000 ft departing from airport A at 20 feet (basically S.L) to airport B which the route course is 026 degrees. I know the standard temp at 5k is 5C. When reviewing at the winds aloft for 5,000 between airport A to airport B, I get an average of 28515-3C which tells me that I have a tailwind of 15 kts. In the POH, it gave a sample problem where the headwind speed of 10 kts is subtracted from the predicted ground speed 109 kts (109-10 = 99kts) giving the new predicted ground speed (more like TAS) of 99 kts.

1). So if you have to minus the ground speed because of a headwind, then I assume you would add when having a tailwind to the ground speed, right? In this case, my predicted ground speed (TAS) is 115 kts and with a tailwind of 15 kts from winds aloft, in order to calculate how much time and fuel, I would do that following and use the final result: 115 + 15 = 130kts. Do I understand that correct??

2). As you may know, in the POH it give 3 columns: 20 below standard temp, standard temp and 20 above standard. As mentioned, the standard temp for 5k is 5C and temperature forecasted for 5k is -03C. So my question is, do I use the -3C and interpolate the values between 20 below standard and standard or do I have it backward where I should be interpolating the values between standard temp and 20 above standard?? (i.e. 5 - (-3) = 8)

Brgds

1). I think you're getting a little confused over speed titles but ending up with the right answers. Any wind component is applied to the True Airspeed to make a Ground Speed. Add tailwinds, subtract headwind components. TAS 100kts with a tail wind of 15kts makes a G/S of 115kts

2). -3C is ISA minus eight. If the temp at 5k should be +5 you would interpolate between the ISA and minus ISA figures.

Maybe buy your instructor a coffee and a burger and have a friendly refresher on flight planning. :)

How did you work out that you had a tailwind of 15kts...?
The wind is 285 at 15... Westerly wind.
You are going 026 degrees i.e. North.
Therefore you have a crosswind.... Recalculate your wind vectors, and find your heading, using whatever Gizmo you have.
If you want to be old school, you could use pencil and paper, and draw the vectors geometrically to scale. 1 inch to 20 kts.

To fly a track of 026 at 99KT TAS with a wind of 285/15, you will need to use a WCA of -9 for a heading of 017. It will give you a 101KT GS. As scifi mentioned, a pretty decent crosswind and certainly not much of a tailwind (all of 2 KT).