Originally Posted by
hans brinker
Be careful with the directs, we use wind planning for best routes on longer legs. I have seen increases in flight time of 15 minutes after getting a direct (off course we didn't take the direct...).
Be careful comparing directs to original route, as (unless winds are known along/abeam waypoints on direct clearance) the time increment cannot be relied upon.
This is the reason why, when all actual winds are used at waypoints, the ABEAM functions in FMC on NG exists, so not to loose valuable data in case of direct clearance...
An operator entering AVG WIND at first waypoint after TOC does so for
preflight planning and estimate of time and fuel on arrival in comparison to flight plan, not for inflight use.
Same operator requiring TOC WIND to be entered (wind after ~20 minutes would be good) does so for optimising fuel burn up to TOC, not for estimate time and fuel on arrival.
Therefore not applying
both above upsets the preflight prediction on longer flights with multiple wind changes, giving inaccurate data for crew to work with, showing incorrect times and fuel prior to flight.
If FMC is left unchanged and no actual winds for each waypoint are entered (which could be done when time permitting preflight or in cruise flight), when executing a direct clearance, last known wind (AVG or TOC in prior example) is used to predict from next waypoint and onward estimates, however actual wind at time of execution is used for prediction to next waypoint.
When getting cleared for a direct clearance of an hour, where FMC entered TWC at TOC was ~100kts, but wind at execution of direct is HWC ~100kts a ~40% groundspeed differential is observed in estimate for next waypoint, this equates to ~25 minutes.
Originally Posted by
The Old Swedish
On a narrow body you can safe up to 15kgs if you land with a reduced flap setting.
On similar narrow body you can save up to 50-70kg if you land using idle reverse thrust which can sometimes only be achieved by wasting those 15kgs saved through use of lower flaps. (Slow it down +15kgs, ability for landing with idle reverse -70kgs, saving 55kgs!)