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