On short haul (A320) flights we are/were usually happy with the average head- or tailwind component which we entered at FMS initialization.
On longhaul flights this gives you a good estimate for the ETA at the beginning of the flight, but not for enroute estimates. Once you pass zones with different wind components, the ETA becomes unreliable as well. In order to have better enroute estimates as well as a reliable ETA, we were entering average wind for legs - each about one hour length (MD11, A330/340).
A few years ago we started entering wind data for all enroute waypoints with a considerable change in wind direction and/or speed at four different levels. This enables the FMS to calculate a optimum level not only depending on weight but also on different wind at different levels. This helped to save fuel by flying more on optimum levels but was quite a bunch of data which had to be entered.
|Quoting CosmicCruiser (Reply 2):|
but then we would up load the forecast winds for about 4 or 5 altitudes on longer flights to add more accuracy
Luckily we have this feature now as well.
"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein