Hi,

I've always only seen GPWT references when it comes to working out PNR's or ETP with different groundspeeds out and home. In the exam a few weeks ago, the question purely listed 'W/V ###/##' with no reference to either unit of measurement. I didn't know which value represented the direction and which number represented the speed.

I'm assuming wind speed is the 3 numbers and V (vector?) is the 2 numbers. Is that right? What exactly does W/V stand for in a PNR context?

Cheers

the question purely listed 'W/V ###/##' with no reference to either unit of measurement.

The AIP is your friend and, if you don't hold a copy, it is available to review on the AirServices website at www.airservicesaustralia.com/aip/aip.asp

W/V means wind/velocity.

The format is DDD/VV where

DDD is degrees magnetic when specified for runway operations. If other than for runway operations, DDD is degrees true.

VV is the wind speed, in knots. In extreme cases, of course, you might see the speed specified in three figures to indicate a speed in excess of 100 kts.

For example, if a forecast, W/V specified as 280/35 means the wind is from direction 280T at a speed of 35 kt.

Conversely, on ATIS, 280/35 means 280M at a speed of 35 knots.

What exactly does W/V stand for in a PNR context?

W/V is just the way the wind is specified and has nothing to do, specifically, with PNRs. Once the W/V is obtained (forecast) or calculated (in flight), it is up to the pilot to run whatever calculations are appropriate to the concern at the time. For a PNR, the preferred approach is to calculate the values for G/S out and return. Although it may give you a small error, you could calculate the wind component and apply it to the TAS value.

Why is there a small error if using wind components ?

When you resolve the W/V to obtain the wind components, you do the appropriate vector resolved components. However, if you then just add a wind component to the TAS, the TAS value is not the appropriate component (think ETAS for those who use the CR navigation computer).

If you ran the resolution and worked out the TAS component (ETAS) then the addition of ETAS + W/C would be fine for the G/S.

This error increases as the drift angle increases.